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rfc:rfc8205

Internet Engineering Task Force (IETF) M. Lepinski, Ed. Request for Comments: 8205 NCF Category: Standards Track K. Sriram, Ed. ISSN: 2070-1721 NIST

                                                        September 2017
                   BGPsec Protocol Specification

Abstract

 This document describes BGPsec, an extension to the Border Gateway
 Protocol (BGP) that provides security for the path of Autonomous
 Systems (ASes) through which a BGP UPDATE message passes.  BGPsec is
 implemented via an optional non-transitive BGP path attribute that
 carries digital signatures produced by each AS that propagates the
 UPDATE message.  The digital signatures provide confidence that every
 AS on the path of ASes listed in the UPDATE message has explicitly
 authorized the advertisement of the route.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8205.

Copyright Notice

 Copyright (c) 2017 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Lepinski & Sriram Standards Track [Page 1] RFC 8205 BGPsec Protocol September 2017

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
 2.  BGPsec Negotiation  . . . . . . . . . . . . . . . . . . . . .   3
   2.1.  The BGPsec Capability . . . . . . . . . . . . . . . . . .   4
   2.2.  Negotiating BGPsec Support  . . . . . . . . . . . . . . .   5
 3.  The BGPsec_PATH Attribute . . . . . . . . . . . . . . . . . .   6
   3.1.  Secure_Path . . . . . . . . . . . . . . . . . . . . . . .   8
   3.2.  Signature_Block . . . . . . . . . . . . . . . . . . . . .  10
 4.  BGPsec UPDATE Messages  . . . . . . . . . . . . . . . . . . .  11
   4.1.  General Guidance  . . . . . . . . . . . . . . . . . . . .  11
   4.2.  Constructing the BGPsec_PATH Attribute  . . . . . . . . .  14
   4.3.  Processing Instructions for Confederation Members . . . .  18
   4.4.  Reconstructing the AS_PATH Attribute  . . . . . . . . . .  19
 5.  Processing a Received BGPsec UPDATE Message . . . . . . . . .  21
   5.1.  Overview of BGPsec Validation . . . . . . . . . . . . . .  22
   5.2.  Validation Algorithm  . . . . . . . . . . . . . . . . . .  23
 6.  Algorithms and Extensibility  . . . . . . . . . . . . . . . .  27
   6.1.  Algorithm Suite Considerations  . . . . . . . . . . . . .  27
   6.2.  Considerations for the SKI Size . . . . . . . . . . . . .  28
   6.3.  Extensibility Considerations  . . . . . . . . . . . . . .  28
 7.  Operations and Management Considerations  . . . . . . . . . .  29
   7.1.  Capability Negotiation Failure  . . . . . . . . . . . . .  29
   7.2.  Preventing Misuse of pCount=0 . . . . . . . . . . . . . .  29
   7.3.  Early Termination of Signature Verification . . . . . . .  30
   7.4.  Non-deterministic Signature Algorithms  . . . . . . . . .  30
   7.5.  Private AS Numbers  . . . . . . . . . . . . . . . . . . .  30
   7.6.  Robustness Considerations for Accessing RPKI Data . . . .  32
   7.7.  Graceful Restart  . . . . . . . . . . . . . . . . . . . .  32
   7.8.  Robustness of Secret Random Number in ECDSA . . . . . . .  32
   7.9.  Incremental/Partial Deployment Considerations . . . . . .  33
 8.  Security Considerations . . . . . . . . . . . . . . . . . . .  33
   8.1.  Security Guarantees . . . . . . . . . . . . . . . . . . .  33
   8.2.  On the Removal of BGPsec Signatures . . . . . . . . . . .  34
   8.3.  Mitigation of Denial-of-Service Attacks . . . . . . . . .  36
   8.4.  Additional Security Considerations  . . . . . . . . . . .  36
 9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  38
 10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  39
   10.1.  Normative References . . . . . . . . . . . . . . . . . .  39
   10.2.  Informative References . . . . . . . . . . . . . . . . .  41
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  43
 Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  44
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  45

Lepinski & Sriram Standards Track [Page 2] RFC 8205 BGPsec Protocol September 2017

1. Introduction

 This document describes BGPsec, a mechanism for providing path
 security for Border Gateway Protocol (BGP) [RFC4271] route
 advertisements.  That is, a BGP speaker who receives a valid BGPsec
 UPDATE message has cryptographic assurance that the advertised route
 has the following property: every Autonomous System (AS) on the path
 of ASes listed in the UPDATE message has explicitly authorized the
 advertisement of the route to the subsequent AS in the path.
 This document specifies an optional (non-transitive) BGP path
 attribute, BGPsec_PATH.  It also describes how a BGPsec-compliant BGP
 speaker (referred to hereafter as a BGPsec speaker) can generate,
 propagate, and validate BGP UPDATE messages containing this attribute
 to obtain the above assurances.
 BGPsec is intended to be used to supplement BGP origin validation
 [RFC6483] [RFC6811], and when used in conjunction with origin
 validation, it is possible to prevent a wide variety of route
 hijacking attacks against BGP.
 BGPsec relies on the Resource Public Key Infrastructure (RPKI)
 certificates that attest to the allocation of AS number and IP
 address resources.  (For more information on the RPKI, see RFC 6480
 [RFC6480] and the documents referenced therein.)  Any BGPsec speaker
 who wishes to send, to external (eBGP) peers, BGP UPDATE messages
 containing the BGPsec_PATH needs to possess a private key associated
 with an RPKI router certificate [RFC8209] that corresponds to the
 BGPsec speaker's AS number.  Note, however, that a BGPsec speaker
 does not need such a certificate in order to validate received UPDATE
 messages containing the BGPsec_PATH attribute (see Section 5.2).

1.1. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

2. BGPsec Negotiation

 This document defines a BGP capability [RFC5492] that allows a BGP
 speaker to advertise to a neighbor the ability to send or to receive
 BGPsec UPDATE messages (i.e., UPDATE messages containing the
 BGPsec_PATH attribute).

Lepinski & Sriram Standards Track [Page 3] RFC 8205 BGPsec Protocol September 2017

2.1. The BGPsec Capability

 This capability has capability code 7.
 The capability length for this capability MUST be set to 3.
 The 3 octets of the capability format are specified in Figure 1.
                 0   1   2   3      4      5   6   7
               +---------------------------------------+
               | Version          | Dir |  Unassigned  |
               +---------------------------------------+
               |                                       |
               +------           AFI              -----+
               |                                       |
               +---------------------------------------+
                  Figure 1: BGPsec Capability Format
 The first 4 bits of the first octet indicate the version of BGPsec
 for which the BGP speaker is advertising support.  This document
 defines only BGPsec version 0 (all 4 bits set to 0).  Other versions
 of BGPsec may be defined in future documents.  A BGPsec speaker MAY
 advertise support for multiple versions of BGPsec by including
 multiple versions of the BGPsec capability in its BGP OPEN message.
 The fifth bit of the first octet is a Direction bit, which indicates
 whether the BGP speaker is advertising the capability to send BGPsec
 UPDATE messages or receive BGPsec UPDATE messages.  The BGP speaker
 sets this bit to 0 to indicate the capability to receive BGPsec
 UPDATE messages.  The BGP speaker sets this bit to 1 to indicate the
 capability to send BGPsec UPDATE messages.
 The remaining 3 bits of the first octet are unassigned and for future
 use.  These bits are set to 0 by the sender of the capability and
 ignored by the receiver of the capability.
 The second and third octets contain the 16-bit Address Family
 Identifier (AFI), which indicates the address family for which the
 BGPsec speaker is advertising support for BGPsec.  This document only
 specifies BGPsec for use with two address families, IPv4 and IPv6,
 with AFI values 1 and 2, respectively [IANA-AF].  BGPsec for use with
 other address families may be specified in future documents.

Lepinski & Sriram Standards Track [Page 4] RFC 8205 BGPsec Protocol September 2017

2.2. Negotiating BGPsec Support

 In order to indicate that a BGP speaker is willing to send BGPsec
 UPDATE messages (for a particular address family), a BGP speaker
 sends the BGPsec capability (see Section 2.1) with the Direction bit
 (the fifth bit of the first octet) set to 1.  In order to indicate
 that the speaker is willing to receive BGP UPDATE messages containing
 the BGPsec_PATH attribute (for a particular address family), a BGP
 speaker sends the BGPsec capability with the Direction bit set to 0.
 In order to advertise the capability to both send and receive BGPsec
 UPDATE messages, the BGP speaker sends two copies of the BGPsec
 capability (one with the Direction bit set to 0 and one with the
 Direction bit set to 1).
 Similarly, if a BGP speaker wishes to use BGPsec with two different
 address families (i.e., IPv4 and IPv6) over the same BGP session,
 then the speaker includes two instances of this capability (one for
 each address family) in the BGP OPEN message.  A BGP speaker MUST NOT
 announce BGPsec capability if it does not support the BGP
 multiprotocol extension [RFC4760].  Additionally, a BGP speaker
 MUST NOT advertise the capability of BGPsec support for a particular
 AFI unless it has also advertised the multiprotocol extension
 capability for the same AFI [RFC4760].
 In a BGPsec peering session, a peer is permitted to send UPDATE
 messages containing the BGPsec_PATH attribute if and only if:
 o  The given peer sent the BGPsec capability for a particular version
    of BGPsec and a particular address family with the Direction bit
    set to 1, and
 o  The other (receiving) peer sent the BGPsec capability for the same
    version of BGPsec and the same address family with the Direction
    bit set to 0.
 In such a session, it can be said that the use of the particular
 version of BGPsec has been negotiated for a particular address
 family.  Traditional BGP UPDATE messages (i.e., unsigned, containing
 the AS_PATH attribute) MAY be sent within a session regardless of
 whether or not the use of BGPsec is successfully negotiated.
 However, if BGPsec is not successfully negotiated, then BGP UPDATE
 messages containing the BGPsec_PATH attribute MUST NOT be sent.
 This document defines the behavior of implementations in the case
 where BGPsec version 0 is the only version that has been successfully
 negotiated.  Any future document that specifies additional versions
 of BGPsec will need to specify behavior in the case that support for
 multiple versions is negotiated.

Lepinski & Sriram Standards Track [Page 5] RFC 8205 BGPsec Protocol September 2017

 BGPsec cannot provide meaningful security guarantees without support
 for 4-byte AS numbers.  Therefore, any BGP speaker that announces the
 BGPsec capability, MUST also announce the capability for 4-byte AS
 support [RFC6793].  If a BGP speaker sends the BGPsec capability but
 not the 4-byte AS support capability, then BGPsec has not been
 successfully negotiated, and UPDATE messages containing the
 BGPsec_PATH attribute MUST NOT be sent within such a session.

3. The BGPsec_PATH Attribute

 The BGPsec_PATH attribute is an optional non-transitive BGP path
 attribute.
 This document registers an attribute type code for this attribute:
 BGPsec_PATH (see Section 9).
 The BGPsec_PATH attribute carries the secured information regarding
 the path of ASes through which an UPDATE message passes.  This
 includes the digital signatures used to protect the path information.
 The UPDATE messages that contain the BGPsec_PATH attribute are
 referred to as "BGPsec UPDATE messages".  The BGPsec_PATH attribute
 replaces the AS_PATH attribute in a BGPsec UPDATE message.  That is,
 UPDATE messages that contain the BGPsec_PATH attribute MUST NOT
 contain the AS_PATH attribute, and vice versa.
 The BGPsec_PATH attribute is made up of several parts.  The
 high-level diagram in Figure 2 provides an overview of the structure
 of the BGPsec_PATH attribute.  ("SKI" as used in Figure 2 means
 "Subject Key Identifier".)

Lepinski & Sriram Standards Track [Page 6] RFC 8205 BGPsec Protocol September 2017

      +---------------------------------------------------------+
      |     +-----------------+                                 |
      |     |   Secure_Path   |                                 |
      |     +-----------------+                                 |
      |     |    pCount X     |                                 |
      |     |    Flags X      |                                 |
      |     |    AS X         |                                 |
      |     |    pCount Y     |                                 |
      |     |    Flags Y      |                                 |
      |     |    AS Y         |                                 |
      |     |      ...        |                                 |
      |     +-----------------+                                 |
      |                                                         |
      |   +---------------------+     +---------------------+   |
      |   |  Signature_Block 1  |     |  Signature_Block 2  |   |
      |   +---------------------+     +---------------------+   |
      |   |  Algorithm Suite 1  |     |  Algorithm Suite 2  |   |
      |   |  SKI X1             |     |  SKI X2             |   |
      |   |  Signature X1       |     |  Signature X2       |   |
      |   |  SKI Y1             |     |  SKI Y2             |   |
      |   |  Signature Y1       |     |  Signature Y2       |   |
      |   |       ...           |     |       ....          |   |
      |   +---------------------+     +---------------------+   |
      |                                                         |
      +---------------------------------------------------------+
       Figure 2: High-Level Diagram of the BGPsec_PATH Attribute
 Figure 3 provides the specification of the format for the BGPsec_PATH
 attribute.
       +-------------------------------------------------------+
       | Secure_Path                             (variable)    |
       +-------------------------------------------------------+
       | Sequence of one or two Signature_Blocks (variable)    |
       +-------------------------------------------------------+
                Figure 3: BGPsec_PATH Attribute Format
 The Secure_Path contains AS path information for the BGPsec UPDATE
 message.  This is logically equivalent to the information that is
 contained in a non-BGPsec AS_PATH attribute.  The information in the
 Secure_Path is used by BGPsec speakers in the same way that
 information from the AS_PATH is used by non-BGPsec speakers.  The
 format of the Secure_Path is described below in Section 3.1.
 The BGPsec_PATH attribute will contain one or two Signature_Blocks,
 each of which corresponds to a different algorithm suite.  Each of

Lepinski & Sriram Standards Track [Page 7] RFC 8205 BGPsec Protocol September 2017

 the Signature_Blocks will contain a Signature Segment for each AS
 number (i.e., Secure_Path Segment) in the Secure_Path.  In the
 most common case, the BGPsec_PATH attribute will contain only a
 single Signature_Block.  However, in order to enable a transition
 from an old algorithm suite to a new algorithm suite (without a
 flag day), it will be necessary to include two Signature_Blocks (one
 for the old algorithm suite and one for the new algorithm suite)
 during the transition period.  (See Section 6.1 for more discussion
 of algorithm transitions.)  The format of the Signature_Blocks is
 described below in Section 3.2.

3.1. Secure_Path

 A detailed description of the Secure_Path information in the
 BGPsec_PATH attribute is provided here.  The specification for the
 Secure_Path field is provided in Figures 4 and 5.
           +-----------------------------------------------+
           | Secure_Path Length                 (2 octets) |
           +-----------------------------------------------+
           | One or more Secure_Path Segments   (variable) |
           +-----------------------------------------------+
                     Figure 4: Secure_Path Format
 The Secure_Path Length contains the length (in octets) of the entire
 Secure_Path (including the 2 octets used to express this length
 field).  As explained below, each Secure_Path Segment is 6 octets
 long.  Note that this means the Secure_Path Length is two greater
 than six times the number of Secure_Path Segments (i.e., the number
 of AS numbers in the path).
 The Secure_Path contains one Secure_Path Segment (see Figure 5) for
 each AS in the path to the originating AS of the prefix specified in
 the UPDATE message.  (Note: Repeated ASes are "compressed out" using
 the pCount field, as discussed below.)
   +------------------------------------------------------+
   | pCount         (1 octet)                             |
   +------------------------------------------------------+
   | Confed_Segment flag (1 bit) |  Unassigned (7 bits)   | (Flags)
   +------------------------------------------------------+
   | AS Number      (4 octets)                            |
   +------------------------------------------------------+
                 Figure 5: Secure_Path Segment Format

Lepinski & Sriram Standards Track [Page 8] RFC 8205 BGPsec Protocol September 2017

 The AS Number (in Figure 5) is the AS number of the BGP speaker that
 added this Secure_Path Segment to the BGPsec_PATH attribute.  (See
 Section 4 for more information on populating this field.)
 The pCount field contains the number of repetitions of the associated
 AS number that the signature covers.  This field enables a BGPsec
 speaker to mimic the semantics of prepending multiple copies of their
 AS to the AS_PATH without requiring the speaker to generate multiple
 signatures.  Note that Section 9.1.2.2 ("Breaking Ties (Phase 2)") in
 [RFC4271] mentions the "number of AS numbers" in the AS_PATH
 attribute that is used in the route selection process.  This metric
 (number of AS numbers) is the same as the AS path length obtained in
 BGPsec by summing the pCount values in the BGPsec_PATH attribute.
 The pCount field is also useful in managing route servers (see
 Section 4.2), AS confederations (see Section 4.3), and AS Number
 migrations (see [RFC8206] for details).
 The leftmost (i.e., the most significant) bit of the Flags field in
 Figure 5 is the Confed_Segment flag.  The Confed_Segment flag is set
 to 1 to indicate that the BGPsec speaker that constructed this
 Secure_Path Segment is sending the UPDATE message to a peer AS within
 the same AS confederation [RFC5065].  (That is, a sequence of
 consecutive Confed_Segment flags are set in a BGPsec UPDATE message
 whenever, in a non-BGPsec UPDATE message, an AS_PATH segment of type
 AS_CONFED_SEQUENCE occurs.)  In all other cases, the Confed_Segment
 flag is set to 0.
 The remaining 7 bits of the Flags field are unassigned.  They MUST be
 set to 0 by the sender and ignored by the receiver.  Note, however,
 that the signature is computed over all 8 bits of the Flags field.
 As stated earlier in Section 2.2, BGPsec peering requires that the
 peering ASes MUST each support 4-byte AS numbers.  Currently assigned
 2-byte AS numbers are converted into 4-byte AS numbers by setting the
 two high-order octets of the 4-octet field to 0 [RFC6793].

Lepinski & Sriram Standards Track [Page 9] RFC 8205 BGPsec Protocol September 2017

3.2. Signature_Block

 A detailed description of the Signature_Blocks in the BGPsec_PATH
 attribute is provided here using Figures 6 and 7.
            +---------------------------------------------+
            | Signature_Block Length         (2 octets)   |
            +---------------------------------------------+
            | Algorithm Suite Identifier     (1 octet)    |
            +---------------------------------------------+
            | Sequence of Signature Segments (variable)   |
            +---------------------------------------------+
                   Figure 6: Signature_Block Format
 The Signature_Block Length in Figure 6 is the total number of octets
 in the Signature_Block (including the 2 octets used to express this
 length field).
 The Algorithm Suite Identifier is a 1-octet identifier specifying the
 digest algorithm and digital signature algorithm used to produce the
 digital signature in each Signature Segment.  An IANA registry of
 algorithm suite identifiers for use in BGPsec is specified in the
 BGPsec algorithms document [RFC8208].
 A Signature_Block in Figure 6 has exactly one Signature Segment (see
 Figure 7) for each Secure_Path Segment in the Secure_Path portion of
 the BGPsec_PATH attribute (that is, one Signature Segment for each
 distinct AS on the path for the prefix in the UPDATE message).
            +---------------------------------------------+
            | Subject Key Identifier (SKI)  (20 octets)   |
            +---------------------------------------------+
            | Signature Length              (2 octets)    |
            +---------------------------------------------+
            | Signature                     (variable)    |
            +---------------------------------------------+
                  Figure 7: Signature Segment Format
 The Subject Key Identifier (SKI) field in Figure 7 contains the value
 in the Subject Key Identifier extension of the RPKI router
 certificate [RFC6487] that is used to verify the signature (see
 Section 5 for details on the validity of BGPsec UPDATE messages).
 The SKI field has a fixed size of 20 octets.  See Section 6.2 for
 considerations for the SKI size.

Lepinski & Sriram Standards Track [Page 10] RFC 8205 BGPsec Protocol September 2017

 The Signature Length field contains the size (in octets) of the value
 in the Signature field of the Signature Segment.
 The Signature field in Figure 7 contains a digital signature that
 protects the prefix and the BGPsec_PATH attribute (see Sections 4 and
 5 for details on signature generation and validation, respectively).

4. BGPsec UPDATE Messages

 Section 4.1 provides general guidance on the creation of BGPsec
 UPDATE messages -- that is, UPDATE messages containing the
 BGPsec_PATH attribute.
 Section 4.2 specifies how a BGPsec speaker generates the BGPsec_PATH
 attribute to include in a BGPsec UPDATE message.
 Section 4.3 contains special processing instructions for members of
 an AS confederation [RFC5065].  A BGPsec speaker that is not a member
 of such a confederation MUST NOT set the Confed_Segment flag in its
 Secure_Path Segment (i.e., leave the Confed_Segment flag at the
 default value of 0) in all BGPsec UPDATE messages it sends.
 Section 4.4 contains instructions for reconstructing the AS_PATH
 attribute in cases where a BGPsec speaker receives an UPDATE message
 with a BGPsec_PATH attribute and wishes to propagate the UPDATE
 message to a peer who does not support BGPsec.

4.1. General Guidance

 The information protected by the signature on a BGPsec UPDATE message
 includes the AS number of the peer to whom the UPDATE message is
 being sent.  Therefore, if a BGPsec speaker wishes to send a BGPsec
 UPDATE message to multiple BGP peers, it MUST generate a separate
 BGPsec UPDATE message for each unique peer AS to whom the UPDATE
 message is sent.
 A BGPsec UPDATE message MUST advertise a route to only a single
 prefix.  This is because a BGPsec speaker receiving an UPDATE message
 with multiple prefixes would be unable to construct a valid BGPsec
 UPDATE message (i.e., valid path signatures) containing a subset of
 the prefixes in the received update.  If a BGPsec speaker wishes to
 advertise routes to multiple prefixes, then it MUST generate a
 separate BGPsec UPDATE message for each prefix.  Additionally, a
 BGPsec UPDATE message MUST use the MP_REACH_NLRI attribute [RFC4760]
 to encode the prefix.

Lepinski & Sriram Standards Track [Page 11] RFC 8205 BGPsec Protocol September 2017

 The BGPsec_PATH attribute and the AS_PATH attribute are mutually
 exclusive.  That is, any UPDATE message containing the BGPsec_PATH
 attribute MUST NOT contain the AS_PATH attribute.  The information
 that would be contained in the AS_PATH attribute is instead conveyed
 in the Secure_Path portion of the BGPsec_PATH attribute.
 In order to create or add a new signature to a BGPsec UPDATE message
 with a given algorithm suite, the BGPsec speaker MUST possess a
 private key suitable for generating signatures for this algorithm
 suite.  Additionally, this private key must correspond to the public
 key in a valid RPKI end entity certificate whose AS number resource
 extension includes the BGPsec speaker's AS number [RFC8209].  Note
 also that new signatures are only added to a BGPsec UPDATE message
 when a BGPsec speaker is generating an UPDATE message to send to an
 external peer (i.e., when the AS number of the peer is not equal to
 the BGPsec speaker's own AS number).
 The RPKI enables the legitimate holder of IP address prefix(es) to
 issue a signed object, called a Route Origin Authorization (ROA),
 that authorizes a given AS to originate routes to a given set of
 prefixes (see RFC 6482 [RFC6482]).  It is expected that most Relying
 Parties (RPs) will utilize BGPsec in tandem with origin validation
 (see RFC 6483 [RFC6483] and RFC 6811 [RFC6811]).  Therefore, it is
 RECOMMENDED that a BGPsec speaker only originate a BGPsec UPDATE
 message advertising a route for a given prefix if there exists a
 valid ROA authorizing the BGPsec speaker's AS to originate routes to
 this prefix.
 If a BGPsec router has received only a non-BGPsec UPDATE message
 containing the AS_PATH attribute (instead of the BGPsec_PATH
 attribute) from a peer for a given prefix, then it MUST NOT attach a
 BGPsec_PATH attribute when it propagates the UPDATE message.  (Note
 that a BGPsec router may also receive a non-BGPsec UPDATE message
 from an internal peer without the AS_PATH attribute, i.e., with just
 the Network Layer Reachability Information (NLRI) in it.  In that
 case, the prefix is originating from that AS, and if it is selected
 for advertisement, the BGPsec speaker SHOULD attach a BGPsec_PATH
 attribute and send a signed route (for that prefix) to its external
 BGPsec-speaking peers.)
 Conversely, if a BGPsec router has received a BGPsec UPDATE message
 (with the BGPsec_PATH attribute) from a peer for a given prefix and
 it chooses to propagate that peer's route for the prefix, then it
 SHOULD propagate the route as a BGPsec UPDATE message containing the
 BGPsec_PATH attribute.

Lepinski & Sriram Standards Track [Page 12] RFC 8205 BGPsec Protocol September 2017

 Note that removing BGPsec signatures (i.e., propagating a route
 advertisement without the BGPsec_PATH attribute) has significant
 security ramifications.  (See Section 8 for a discussion of the
 security ramifications of removing BGPsec signatures.)  Therefore,
 when a route advertisement is received via a BGPsec UPDATE message,
 propagating the route advertisement without the BGPsec_PATH attribute
 is NOT RECOMMENDED, unless the message is sent to a peer that did not
 advertise the capability to receive BGPsec UPDATE messages (see
 Section 4.4).
 Furthermore, note that when a BGPsec speaker propagates a route
 advertisement with the BGPsec_PATH attribute, it is not attesting to
 the validation state of the UPDATE message it received.  (See
 Section 8 for more discussion of the security semantics of BGPsec
 signatures.)
 If the BGPsec speaker is producing an UPDATE message that would, in
 the absence of BGPsec, contain an AS_SET (e.g., the BGPsec speaker is
 performing proxy aggregation), then the BGPsec speaker MUST NOT
 include the BGPsec_PATH attribute.  In such a case, the BGPsec
 speaker MUST remove any existing BGPsec_PATH in the received
 advertisement(s) for this prefix and produce a traditional
 (non-BGPsec) UPDATE message.  It should be noted that BCP 172
 [RFC6472] recommends against the use of AS_SET and AS_CONFED_SET in
 the AS_PATH of BGP UPDATE messages.
 The case where the BGPsec speaker sends a BGPsec UPDATE message to an
 iBGP (internal BGP) peer is quite simple.  When originating a new
 route advertisement and sending it to a BGPsec-capable iBGP peer, the
 BGPsec speaker omits the BGPsec_PATH attribute.  When originating a
 new route advertisement and sending it to a non-BGPsec iBGP peer, the
 BGPsec speaker includes an empty AS_PATH attribute in the UPDATE
 message.  (An empty AS_PATH attribute is one whose length field
 contains the value 0 [RFC4271].)  When a BGPsec speaker chooses to
 forward a BGPsec UPDATE message to an iBGP peer, the BGPsec_PATH
 attribute SHOULD NOT be removed, unless the peer doesn't support
 BGPsec.  In the case when an iBGP peer doesn't support BGPsec, then a
 BGP UPDATE message with AS_PATH is reconstructed from the BGPsec
 UPDATE message and then forwarded (see Section 4.4).  In particular,
 when forwarding to a BGPsec-capable iBGP (or eBGP) peer, the
 BGPsec_PATH attribute SHOULD NOT be removed even in the case where
 the BGPsec UPDATE message has not been successfully validated.  (See
 Section 5 for more information on validation and Section 8 for the
 security ramifications of removing BGPsec signatures.)

Lepinski & Sriram Standards Track [Page 13] RFC 8205 BGPsec Protocol September 2017

 All BGPsec UPDATE messages MUST conform to BGP's maximum message
 size.  If the resulting message exceeds the maximum message size,
 then the guidelines in Section 9.2 of RFC 4271 [RFC4271] MUST be
 followed.

4.2. Constructing the BGPsec_PATH Attribute

 When a BGPsec speaker receives a BGPsec UPDATE message containing a
 BGPsec_PATH attribute (with one or more signatures) from an (internal
 or external) peer, it may choose to propagate the route advertisement
 by sending it to its other (internal or external) peers.  When
 sending the route advertisement to an internal BGPsec-speaking peer,
 the BGPsec_PATH attribute SHALL NOT be modified.  When sending the
 route advertisement to an external BGPsec-speaking peer, the
 following procedures are used to form or update the BGPsec_PATH
 attribute.
 To generate the BGPsec_PATH attribute on the outgoing UPDATE message,
 the BGPsec speaker first generates a new Secure_Path Segment.  Note
 that if the BGPsec speaker is not the origin AS and there is an
 existing BGPsec_PATH attribute, then the BGPsec speaker prepends its
 new Secure_Path Segment (places in first position) onto the existing
 Secure_Path.
 The AS number in this Secure_Path Segment MUST match the AS number in
 the Subject field of the RPKI router certificate that will be used to
 verify the digital signature constructed by this BGPsec speaker (see
 Section 3.1.1 in [RFC8209] and RFC 6487 [RFC6487]).
 The pCount field of the Secure_Path Segment is typically set to the
 value 1.  However, a BGPsec speaker may set the pCount field to a
 value greater than 1.  Setting the pCount field to a value greater
 than 1 has the same semantics as repeating an AS number multiple
 times in the AS_PATH of a non-BGPsec UPDATE message (e.g., for
 traffic engineering purposes).
 To prevent unnecessary processing load in the validation of BGPsec
 signatures, a BGPsec speaker SHOULD NOT produce multiple consecutive
 Secure_Path Segments with the same AS number.  This means that to
 achieve the semantics of prepending the same AS number k times, a
 BGPsec speaker SHOULD produce a single Secure_Path Segment -- with a
 pCount of k -- and a single corresponding Signature Segment.
 A route server that participates in the BGP control plane but
 does not act as a transit AS in the data plane may choose to set
 pCount to 0.  This option enables the route server to participate in
 BGPsec and obtain the associated security guarantees without
 increasing the length of the AS path.  (Note that BGPsec speakers

Lepinski & Sriram Standards Track [Page 14] RFC 8205 BGPsec Protocol September 2017

 compute the length of the AS path by summing the pCount values in the
 BGPsec_PATH attribute; see Section 5.)  However, when a route server
 sets the pCount value to 0, it still inserts its AS number into the
 Secure_Path Segment, as this information is needed to validate the
 signature added by the route server.  See [RFC8206] for a discussion
 of setting pCount to 0 to facilitate AS Number migration.  Also, see
 Section 4.3 for the use of pCount=0 in the context of an AS
 confederation.  See Section 7.2 for operational guidance for
 configuring a BGPsec router for setting pCount=0 and/or accepting
 pCount=0 from a peer.
 Next, the BGPsec speaker generates one or two Signature_Blocks.
 Typically, a BGPsec speaker will use only a single algorithm suite
 and thus create only a single Signature_Block in the BGPsec_PATH
 attribute.  However, to ensure backwards compatibility during a
 period of transition from a 'current' algorithm suite to a 'new'
 algorithm suite, it will be necessary to originate UPDATE messages
 that contain a Signature_Block for both the 'current' and the 'new'
 algorithm suites (see Section 6.1).
 If the received BGPsec UPDATE message contains two Signature_Blocks
 and the BGPsec speaker supports both of the corresponding algorithm
 suites, then the new UPDATE message generated by the BGPsec speaker
 MUST include both of the Signature_Blocks.  If the received BGPsec
 UPDATE message contains two Signature_Blocks and the BGPsec speaker
 only supports one of the two corresponding algorithm suites, then the
 BGPsec speaker MUST remove the Signature_Block corresponding to the
 algorithm suite that it does not understand.  If the BGPsec speaker
 does not support the algorithm suites in any of the Signature_Blocks
 contained in the received UPDATE message, then the BGPsec speaker
 MUST NOT propagate the route advertisement with the BGPsec_PATH
 attribute.  (That is, if it chooses to propagate this route
 advertisement at all, it MUST do so as an unsigned BGP UPDATE
 message.  See Section 4.4 for more information on converting to an
 unsigned BGP UPDATE message.)
 Note that in the case where the BGPsec_PATH has two Signature_Blocks
 (corresponding to different algorithm suites), the validation
 algorithm (see Section 5.2) deems a BGPsec UPDATE message to be
 'Valid' if there is at least one supported algorithm suite (and
 corresponding Signature_Block) that is deemed 'Valid'.  This means
 that a 'Valid' BGPsec UPDATE message may contain a Signature_Block
 that is not deemed 'Valid' (e.g., contains signatures that BGPsec
 does not successfully verify).  Nonetheless, such Signature_Blocks
 MUST NOT be removed.  (See Section 8 for a discussion of the security
 ramifications of this design choice.)

Lepinski & Sriram Standards Track [Page 15] RFC 8205 BGPsec Protocol September 2017

 For each Signature_Block corresponding to an algorithm suite that the
 BGPsec speaker does support, the BGPsec speaker MUST add a new
 Signature Segment to the Signature_Block.  This Signature Segment is
 prepended to the list of Signature Segments (placed in the first
 position) so that the list of Signature Segments appears in the same
 order as the corresponding Secure_Path Segments.  The BGPsec speaker
 populates the fields of this new Signature Segment as follows.
 The Subject Key Identifier field in the new segment is populated with
 the identifier contained in the Subject Key Identifier extension of
 the RPKI router certificate corresponding to the BGPsec speaker
 [RFC8209].  This Subject Key Identifier will be used by recipients of
 the route advertisement to identify the proper certificate to use in
 verifying the signature.
 The Signature field in the new segment contains a digital signature
 that binds the prefix and BGPsec_PATH attribute to the RPKI router
 certificate corresponding to the BGPsec speaker.  The digital
 signature is computed as follows:
 o  For clarity, let us number the Secure_Path and corresponding
    Signature Segments from 1 to N, as follows.  Let Secure_Path
    Segment 1 and Signature Segment 1 be the segments produced by the
    origin AS.  Let Secure_Path Segment 2 and Signature Segment 2 be
    the segments added by the next AS after the origin.  Continue this
    method of numbering, and ultimately let Secure_Path Segment N and
    Signature Segment N be those that are being added by the current
    AS.  The current AS (Nth AS) is signing and forwarding the UPDATE
    message to the next AS (i.e., the (N+1)th AS) in the chain of ASes
    that form the AS path.
 o  In order to construct the digital signature for Signature
    Segment N (the Signature Segment being produced by the current
    AS), first construct the sequence of octets to be hashed as shown
    in Figure 8.  This sequence of octets includes all the data that
    the Nth AS attests to by adding its digital signature in the
    UPDATE message that is being forwarded to a BGPsec speaker in the
    (N+1)th AS.  (For the design rationale for choosing the specific
    structure in Figure 8, please see [Borchert].)

Lepinski & Sriram Standards Track [Page 16] RFC 8205 BGPsec Protocol September 2017

             +------------------------------------+
             | Target AS Number                   |
             +------------------------------------+----\
             | Signature Segment   : N-1          |     \
             +------------------------------------+     |
             | Secure_Path Segment : N            |     |
             +------------------------------------+     \
                    ...                                  >  Data from
             +------------------------------------+     /   N Segments
             | Signature Segment   : 1            |     |
             +------------------------------------+     |
             | Secure_Path Segment : 2            |     |
             +------------------------------------+     /
             | Secure_Path Segment : 1            |    /
             +------------------------------------+---/
             | Algorithm Suite Identifier         |
             +------------------------------------+
             | AFI                                |
             +------------------------------------+
             | SAFI                               |
             +------------------------------------+
             | NLRI                               |
             +------------------------------------+
               Figure 8: Sequence of Octets to Be Hashed
    The elements in this sequence (Figure 8) MUST be ordered exactly
    as shown.  The 'Target AS Number' is the AS to whom the BGPsec
    speaker intends to send the UPDATE message.  (Note that the
    'Target AS Number' is the AS number announced by the peer in the
    OPEN message of the BGP session within which the UPDATE message is
    sent.)  The Secure_Path and Signature Segments (1 through N-1) are
    obtained from the BGPsec_PATH attribute.  Finally, the Address
    Family Identifier (AFI), Subsequent Address Family Identifier
    (SAFI), and NLRI fields are obtained from the MP_REACH_NLRI
    attribute [RFC4760].  Additionally, in the Prefix field within the
    NLRI field (see Section 5 in RFC 4760 [RFC4760]), all of the
    trailing bits MUST be set to 0 when constructing this sequence.
 o  Apply to this octet sequence (in Figure 8) the digest algorithm
    (for the algorithm suite of this Signature_Block) to obtain a
    digest value.
 o  Apply to this digest value the signature algorithm (for the
    algorithm suite of this Signature_Block) to obtain the digital
    signature.  Then populate the Signature field (in Figure 7) with
    this digital signature.

Lepinski & Sriram Standards Track [Page 17] RFC 8205 BGPsec Protocol September 2017

 The Signature Length field (in Figure 7) is populated with the length
 (in octets) of the value in the Signature field.

4.3. Processing Instructions for Confederation Members

 Members of AS confederations [RFC5065] MUST additionally follow the
 instructions in this section for processing BGPsec UPDATE messages.
 When a BGPsec speaker in an AS confederation receives a BGPsec UPDATE
 message from a peer that is external to the confederation and chooses
 to propagate the UPDATE message within the confederation, it first
 adds a signature signed to its own Member-AS (i.e., the 'Target AS
 Number' is the BGPsec speaker's Member-AS Number).  In this
 internally modified UPDATE message, the newly added Secure_Path
 Segment contains the public AS number (i.e., Confederation
 Identifier), the segment's pCount value is set to 0, and
 Confed_Segment flag is set to 1.  Setting pCount=0 in this case helps
 ensure that the AS path length is not unnecessarily incremented.  The
 newly added signature is generated using a private key corresponding
 to the public AS number of the confederation.  The BGPsec speaker
 propagates the modified UPDATE message to its peers within the
 confederation.
 Any BGPsec_PATH modifications mentioned below in the context of
 propagation of the UPDATE message within the confederation are in
 addition to the modification described above (i.e., with pCount=0).
 When a BGPsec speaker sends a BGPsec UPDATE message to a peer that
 belongs within its own Member-AS, the confederation member SHALL NOT
 modify the BGPsec_PATH attribute.  When a BGPsec speaker sends a
 BGPsec UPDATE message to a peer that is within the same confederation
 but in a different Member-AS, the BGPsec speaker puts its Member-AS
 Number in the AS Number field of the Secure_Path Segment that it adds
 to the BGPsec UPDATE message.  Additionally, in this case, the
 Member-AS that generates the Secure_Path Segment sets the
 Confed_Segment flag to 1.  Further, the signature is generated with a
 private key corresponding to the BGPsec speaker's Member-AS Number.
 (Note: In this document, intra-Member-AS peering is regarded as iBGP,
 and inter-Member-AS peering is regarded as eBGP.  The latter is also
 known as confederation-eBGP.)
 Within a confederation, the verification of BGPsec signatures added
 by other members of the confederation is optional.  Note that if a
 confederation chooses not to verify digital signatures within the
 confederation, then BGPsec is not able to provide any assurances
 about the integrity of the Member-AS Numbers placed in Secure_Path
 Segments where the Confed_Segment flag is set to 1.

Lepinski & Sriram Standards Track [Page 18] RFC 8205 BGPsec Protocol September 2017

 When a confederation member receives a BGPsec UPDATE message from a
 peer within the confederation and propagates it to a peer outside the
 confederation, it needs to remove all of the Secure_Path Segments
 added by confederation members as well as the corresponding Signature
 Segments.  To do this, the confederation member propagating the route
 outside the confederation does the following:
 o  First, starting with the most recently added Secure_Path Segment,
    remove all of the consecutive Secure_Path Segments that have the
    Confed_Segment flag set to 1.  Stop this process once a
    Secure_Path Segment that has its Confed_Segment flag set to 0 is
    reached.  Keep a count of the number of segments removed in this
    fashion.
 o  Second, starting with the most recently added Signature Segment,
    remove a number of Signature Segments equal to the number of
    Secure_Path Segments removed in the previous step.  (That is,
    remove the K most recently added Signature Segments, where K is
    the number of Secure_Path Segments removed in the previous step.)
 o  Finally, add a Secure_Path Segment containing, in the AS field,
    the AS Confederation Identifier (the public AS number of the
    confederation) as well as a corresponding Signature Segment.  Note
    that all fields other than the AS field are populated as per
    Section 4.2.
 Finally, as discussed above, an AS confederation MAY optionally
 decide that its members will not verify digital signatures added by
 members.  In such a confederation, when a BGPsec speaker runs the
 algorithm in Section 5.2, the BGPsec speaker, during the process of
 signature verifications, first checks whether the Confed_Segment flag
 in a Secure_Path Segment is set to 1.  If the flag is set to 1, the
 BGPsec speaker skips the verification for the corresponding signature
 and immediately moves on to the next Secure_Path Segment.  Note that
 as specified in Section 5.2, it is an error when a BGPsec speaker
 receives, from a peer who is not in the same AS confederation, a
 BGPsec UPDATE message containing a Confed_Segment flag set to 1.

4.4. Reconstructing the AS_PATH Attribute

 BGPsec UPDATE messages do not contain the AS_PATH attribute.
 However, the AS_PATH attribute can be reconstructed from the
 BGPsec_PATH attribute.  This is necessary in the case where a route
 advertisement is received via a BGPsec UPDATE message and then
 propagated to a peer via a non-BGPsec UPDATE message (e.g., because
 the latter peer does not support BGPsec).  Note that there may be
 additional cases where an implementation finds it useful to perform
 this reconstruction.  Before attempting to reconstruct an AS_PATH for

Lepinski & Sriram Standards Track [Page 19] RFC 8205 BGPsec Protocol September 2017

 the purpose of forwarding an unsigned (non-BGPsec) UPDATE message to
 a peer, a BGPsec speaker MUST perform the basic integrity checks
 listed in Section 5.2 to ensure that the received BGPsec UPDATE
 message is properly formed.
 The AS_PATH attribute can be constructed from the BGPsec_PATH
 attribute as follows.  Starting with a blank AS_PATH attribute,
 process the Secure_Path Segments in order from least recently added
 (corresponding to the origin) to most recently added.  For each
 Secure_Path Segment, perform the following steps:
 1.  If the Secure_Path Segment has pCount=0, then do nothing (i.e.,
     move on to process the next Secure_Path Segment).
 2.  If the Secure_Path Segment has pCount greater than 0 and the
     Confed_Segment flag is set to 1, then look at the most recently
     added segment in the AS_PATH.
  • In the case where the AS_PATH is blank or in the case where

the most recently added segment is of type AS_SEQUENCE, add

        (prepend to the AS_PATH) a new AS_PATH segment of type
        AS_CONFED_SEQUENCE.  This segment of type AS_CONFED_SEQUENCE
        shall contain a number of elements equal to the pCount field
        in the current Secure_Path Segment.  Each of these elements
        shall be the AS number contained in the current Secure_Path
        Segment.  (That is, if the pCount field is X, then the segment
        of type AS_CONFED_SEQUENCE contains X copies of the
        Secure_Path Segment's AS Number field.)
  • In the case where the most recently added segment in the

AS_PATH is of type AS_CONFED_SEQUENCE, then add (prepend to

        the segment) a number of elements equal to the pCount field in
        the current Secure_Path Segment.  The value of each of these
        elements shall be the AS number contained in the current
        Secure_Path Segment.  (That is, if the pCount field is X, then
        add X copies of the Secure_Path Segment's AS Number field to
        the existing AS_CONFED_SEQUENCE.)
 3.  If the Secure_Path Segment has pCount greater than 0 and the
     Confed_Segment flag is set to 0, then look at the most recently
     added segment in the AS_PATH.
  • In the case where the AS_PATH is blank or in the case where

the most recently added segment is of type AS_CONFED_SEQUENCE,

        add (prepend to the AS_PATH) a new AS_PATH segment of type
        AS_SEQUENCE.  This segment of type AS_SEQUENCE shall contain a
        number of elements equal to the pCount field in the current
        Secure_Path Segment.  Each of these elements shall be the AS

Lepinski & Sriram Standards Track [Page 20] RFC 8205 BGPsec Protocol September 2017

        number contained in the current Secure_Path Segment.  (That
        is, if the pCount field is X, then the segment of type
        AS_SEQUENCE contains X copies of the Secure_Path Segment's AS
        Number field.)
  • In the case where the most recently added segment in the

AS_PATH is of type AS_SEQUENCE, then add (prepend to the

        segment) a number of elements equal to the pCount field in the
        current Secure_Path Segment.  The value of each of these
        elements shall be the AS number contained in the current
        Secure_Path Segment.  (That is, if the pCount field is X, then
        add X copies of the Secure_Path Segment's AS Number field to
        the existing AS_SEQUENCE.)
 As part of the procedure described above, the following additional
 actions are performed in order not to exceed the size limitations of
 AS_SEQUENCE and AS_CONFED_SEQUENCE.  While adding the next
 Secure_Path Segment (with its prepends, if any) to the AS_PATH being
 assembled, if it would cause the AS_SEQUENCE (or AS_CONFED_SEQUENCE)
 at hand to exceed the limit of 255 AS numbers per segment [RFC4271]
 [RFC5065], then the BGPsec speaker would follow the recommendations
 in RFC 4271 [RFC4271] and RFC 5065 [RFC5065] of creating another
 segment of the same type (AS_SEQUENCE or AS_CONFED_SEQUENCE) and
 continue filling that.
 Finally, one special case of reconstruction of AS_PATH is when the
 BGPsec_PATH attribute is absent.  As explained in Section 4.1, when a
 BGPsec speaker originates a prefix and sends it to a BGPsec-capable
 iBGP peer, the BGPsec_PATH is not attached.  So, when received from a
 BGPsec-capable iBGP peer, no BGPsec_PATH attribute in a BGPsec UPDATE
 message is equivalent to an empty AS_PATH [RFC4271].

5. Processing a Received BGPsec UPDATE Message

 Upon receiving a BGPsec UPDATE message from an external (eBGP) peer,
 a BGPsec speaker SHOULD validate the message to determine the
 authenticity of the path information contained in the BGPsec_PATH
 attribute.  Typically, a BGPsec speaker will also wish to perform
 origin validation (see RFC 6483 [RFC6483] and RFC 6811 [RFC6811]) on
 an incoming BGPsec UPDATE message, but such validation is independent
 of the validation described in this section.
 Section 5.1 provides an overview of BGPsec validation, and
 Section 5.2 provides a specific algorithm for performing such
 validation.  (Note that an implementation need not follow the
 specific algorithm in Section 5.2 as long as the input/output
 behavior of the validation is identical to that of the algorithm in
 Section 5.2.)  During exceptional conditions (e.g., the BGPsec

Lepinski & Sriram Standards Track [Page 21] RFC 8205 BGPsec Protocol September 2017

 speaker receives an incredibly large number of UPDATE messages at
 once), a BGPsec speaker MAY temporarily defer validation of incoming
 BGPsec UPDATE messages.  The treatment of such BGPsec UPDATE
 messages, whose validation has been deferred, is a matter of local
 policy.  However, an implementation SHOULD ensure that deferment of
 validation and status of deferred messages is visible to the
 operator.
 The validity of BGPsec UPDATE messages is a function of the current
 RPKI state.  When a BGPsec speaker learns that the RPKI state has
 changed (e.g., from an RPKI validating cache via the RPKI-Router
 protocol [RFC8210]), the BGPsec speaker MUST rerun validation on all
 affected UPDATE messages stored in its Adj-RIB-In [RFC4271].  For
 example, when a given RPKI router certificate ceases to be valid
 (e.g., it expires or is revoked), all UPDATE messages containing a
 signature whose SKI matches the SKI in the given certificate MUST be
 reassessed to determine if they are still valid.  If this
 reassessment determines that the validity state of an UPDATE message
 has changed, then, depending on local policy, it may be necessary to
 rerun best path selection.
 BGPsec UPDATE messages do not contain an AS_PATH attribute.  The
 Secure_Path contains AS path information for the BGPsec UPDATE
 message.  Therefore, a BGPsec speaker MUST utilize the AS path
 information in the Secure_Path in all cases where it would otherwise
 use the AS path information in the AS_PATH attribute.  The only
 exception to this rule is when AS path information must be updated in
 order to propagate a route to a peer (in which case the BGPsec
 speaker follows the instructions in Section 4).  Section 4.4 provides
 an algorithm for constructing an AS_PATH attribute from a BGPsec_PATH
 attribute.  Whenever the use of AS path information is called for
 (e.g., loop detection or the use of the AS path length in best path
 selection), the externally visible behavior of the implementation
 shall be the same as if the implementation had run the algorithm in
 Section 4.4 and used the resulting AS_PATH attribute as it would for
 a non-BGPsec UPDATE message.

5.1. Overview of BGPsec Validation

 Validation of a BGPsec UPDATE message makes use of data from RPKI
 router certificates.  In particular, it is necessary that the
 recipient have access to the following data obtained from valid RPKI
 router certificates: the AS Number, Public Key, and Subject Key
 Identifier from each valid RPKI router certificate.
 Note that the BGPsec speaker could perform the validation of RPKI
 router certificates on its own and extract the required data, or it
 could receive the same data from a trusted cache that performs RPKI

Lepinski & Sriram Standards Track [Page 22] RFC 8205 BGPsec Protocol September 2017

 validation on behalf of (some set of) BGPsec speakers.  (For example,
 the trusted cache could deliver the necessary validity information to
 the BGPsec speaker by using the Router Key PDU (Protocol Data Unit)
 for the RPKI-Router protocol [RFC8210].)
 To validate a BGPsec UPDATE message containing the BGPsec_PATH
 attribute, the recipient performs the validation steps specified in
 Section 5.2.  The validation procedure results in one of two states:
 'Valid' and 'Not Valid'.
 It is expected that the output of the validation procedure will be
 used as an input to BGP route selection.  That said, BGP route
 selection, and thus the handling of the validation states, is a
 matter of local policy and is handled using local policy mechanisms.
 Implementations SHOULD enable operators to set such local policy on a
 per-session basis.  (That is, it is expected that some operators will
 choose to treat BGPsec validation status differently for UPDATE
 messages received over different BGP sessions.)
 BGPsec validation need only be performed at the eBGP edge.  The
 validation status of a BGP signed/unsigned UPDATE message MAY be
 conveyed via iBGP from an ingress edge router to an egress edge
 router via some mechanism, according to local policy within an AS.
 As discussed in Section 4, when a BGPsec speaker chooses to forward a
 (syntactically correct) BGPsec UPDATE message, it SHOULD be forwarded
 with its BGPsec_PATH attribute intact (regardless of the validation
 state of the UPDATE message).  Based entirely on local policy, an
 egress router receiving a BGPsec UPDATE message from within its own
 AS MAY choose to perform its own validation.

5.2. Validation Algorithm

 This section specifies an algorithm for validation of BGPsec UPDATE
 messages.  A conformant implementation MUST include a BGPsec update
 validation algorithm that is functionally equivalent to the
 externally visible behavior of this algorithm.
 First, the recipient of a BGPsec UPDATE message performs a check to
 ensure that the message is properly formed.  Both syntactical and
 protocol violation errors are checked.  The BGPsec_PATH attribute
 MUST be present when a BGPsec UPDATE message is received from an
 external (eBGP) BGPsec peer and also when such an UPDATE message is
 propagated to an internal (iBGP) BGPsec peer (see Section 4.2).  The
 error checks specified in Section 6.3 of [RFC4271] are performed,
 except that for BGPsec UPDATE messages the checks on the AS_PATH
 attribute do not apply and instead the following checks on the
 BGPsec_PATH attribute are performed:

Lepinski & Sriram Standards Track [Page 23] RFC 8205 BGPsec Protocol September 2017

 1.  Check to ensure that the entire BGPsec_PATH attribute is
     syntactically correct (conforms to the specification in this
     document).
 2.  Check that the AS number in the most recently added Secure_Path
     Segment (i.e., the one corresponding to the eBGP peer from which
     the UPDATE message was received) matches the AS number of that
     peer as specified in the BGP OPEN message.  (Note: This check is
     performed only at an ingress BGPsec router where the UPDATE
     message is first received from a peer AS.)
 3.  Check that each Signature_Block contains one Signature Segment
     for each Secure_Path Segment in the Secure_Path portion of the
     BGPsec_PATH attribute.  (Note that the entirety of each
     Signature_Block MUST be checked to ensure that it is well formed,
     even though the validation process may terminate before all
     signatures are cryptographically verified.)
 4.  Check that the UPDATE message does not contain an AS_PATH
     attribute.
 5.  If the UPDATE message was received from a BGPsec peer that is not
     a member of the BGPsec speaker's AS confederation, check to
     ensure that none of the Secure_Path Segments contain a Flags
     field with the Confed_Segment flag set to 1.
 6.  If the UPDATE message was received from a BGPsec peer that is a
     member of the BGPsec speaker's AS confederation, check to ensure
     that the Secure_Path Segment corresponding to that peer contains
     a Flags field with the Confed_Segment flag set to 1.
 7.  If the UPDATE message was received from a peer that is not
     expected to set pCount=0 (see Sections 4.2 and 4.3), then check
     to ensure that the pCount field in the most recently added
     Secure_Path Segment is not equal to 0.  (Note: See Section 7.2
     for router configuration guidance related to this item.)
 8.  Using the equivalent of AS_PATH corresponding to the Secure_Path
     in the UPDATE message (see Section 4.4), check that the local AS
     number is not present in the AS path (i.e., rule out an AS loop).
 If any of these checks fail, it is an error in the BGPsec_PATH
 attribute.  BGPsec speakers MUST handle any syntactical or protocol
 errors in the BGPsec_PATH attribute by using the "treat-as-withdraw"
 approach as defined in RFC 7606 [RFC7606].  (Note: Since the AS
 number of a transparent route server does appear in the Secure_Path
 with pCount=0, the route server MAY check to see if its local AS is

Lepinski & Sriram Standards Track [Page 24] RFC 8205 BGPsec Protocol September 2017

 listed in the Secure_Path, and this check MAY be included in the
 loop-detection check listed above.)
 Next, the BGPsec speaker examines the Signature_Blocks in the
 BGPsec_PATH attribute.  A Signature_Block corresponding to an
 algorithm suite that the BGPsec speaker does not support is not
 considered in the validation process.  If there is no Signature_Block
 corresponding to an algorithm suite that the BGPsec speaker supports,
 then in order to consider the UPDATE message in the route selection
 process, the BGPsec speaker MUST strip the Signature_Block(s),
 reconstruct the AS_PATH from the Secure_Path (see Section 4.4), and
 treat the UPDATE message as if it were received as an unsigned BGP
 UPDATE message.
 For each remaining Signature_Block (corresponding to an algorithm
 suite supported by the BGPsec speaker), the BGPsec speaker iterates
 through the Signature Segments in the Signature_Block, starting with
 the most recently added segment (and concluding with the
 least recently added segment).  Note that there is a one-to-one
 correspondence between Signature Segments and Secure_Path Segments
 within the BGPsec_PATH attribute.  The following steps make use of
 this correspondence:
 o  Step 1: Let there be K AS hops in a received BGPsec_PATH attribute
    that is to be validated.  Let AS(1), AS(2), ..., AS(K+1) denote
    the sequence of AS numbers from the origin AS to the validating
    AS.  Let Secure_Path Segment N and Signature Segment N in the
    BGPsec_PATH attribute refer to those corresponding to AS(N) (where
    N = 1, 2, ..., K).  The BGPsec speaker that is processing and
    validating the BGPsec_PATH attribute resides in AS(K+1).  Let
    Signature Segment N be the Signature Segment that is currently
    being verified.
 o  Step 2: Locate the public key needed to verify the signature (in
    the current Signature Segment).  To do this, consult the valid
    RPKI router certificate data and look up all valid (AS Number,
    Public Key, Subject Key Identifier) triples in which the AS
    matches the AS number in the corresponding Secure_Path Segment.
    Of these triples that match the AS number, check whether there is
    an SKI that matches the value in the Subject Key Identifier field
    of the Signature Segment.  If this check finds no such matching
    SKI value, then mark the entire Signature_Block as 'Not Valid' and
    proceed to the next Signature_Block.
 o  Step 3: Compute the digest function (for the given algorithm
    suite) on the appropriate data.

Lepinski & Sriram Standards Track [Page 25] RFC 8205 BGPsec Protocol September 2017

    In order to verify the digital signature in Signature Segment N,
    construct the sequence of octets to be hashed as shown in Figure 9
    (using the notations defined in Step 1).  (Note that this sequence
    is the same sequence that was used by AS(N) that created the
    Signature Segment N (see Section 4.2 and Figure 8).)
       +------------------------------------+
       | Target AS Number                   |
       +------------------------------------+----\
       | Signature Segment   : N-1          |     \
       +------------------------------------+     |
       | Secure_Path Segment : N            |     |
       +------------------------------------+     \
              ...                                  >  Data from
       +------------------------------------+     /   N Segments
       | Signature Segment   : 1            |     |
       +------------------------------------+     |
       | Secure_Path Segment : 2            |     |
       +------------------------------------+     /
       | Secure_Path Segment : 1            |    /
       +------------------------------------+---/
       | Algorithm Suite Identifier         |
       +------------------------------------+
       | AFI                                |
       +------------------------------------+
       | SAFI                               |
       +------------------------------------+
       | NLRI                               |
       +------------------------------------+
 Figure 9: Sequence of Octets to Be Hashed for Signature Verification
   of Signature Segment N; N = 1,2, ..., K, Where K Is the Number of
                 AS Hops in the BGPsec_PATH Attribute
    The elements in this sequence (Figure 9) MUST be ordered exactly
    as shown.  For the first segment to be processed (the
    most recently added segment (i.e., N = K) given that there are K
    hops in the Secure_Path), the 'Target AS Number' is AS(K+1), the
    AS number of the BGPsec speaker validating the UPDATE message.
    Note that if a BGPsec speaker uses multiple AS Numbers (e.g., the
    BGPsec speaker is a member of a confederation), the AS number used
    here MUST be the AS number announced in the OPEN message for the
    BGP session over which the BGPsec UPDATE message was received.
    For each other Signature Segment (N smaller than K), the 'Target
    AS Number' is AS(N+1), the AS number in the Secure_Path Segment
    that corresponds to the Signature Segment added immediately after
    the one being processed (that is, in the Secure_Path Segment that

Lepinski & Sriram Standards Track [Page 26] RFC 8205 BGPsec Protocol September 2017

    corresponds to the Signature Segment that the validator just
    finished processing).
    The Secure_Path and Signature Segment are obtained from the
    BGPsec_PATH attribute.  The AFI, SAFI, and NLRI fields are
    obtained from the MP_REACH_NLRI attribute [RFC4760].
    Additionally, in the Prefix field within the NLRI field (see
    Section 5 in RFC 4760 [RFC4760]), all of the trailing bits MUST be
    set to 0 when constructing this sequence.
 o  Step 4: Use the signature validation algorithm (for the given
    algorithm suite) to verify the signature in the current segment.
    That is, invoke the signature validation algorithm on the
    following three inputs: the value of the Signature field in the
    current segment, the digest value computed in Step 3 above, and
    the public key obtained from the valid RPKI data in Step 2 above.
    If the signature validation algorithm determines that the
    signature is invalid, then mark the entire Signature_Block as
    'Not Valid' and proceed to the next Signature_Block.  If the
    signature validation algorithm determines that the signature is
    valid, then continue processing Signature Segments (within the
    current Signature_Block).
 If all Signature Segments within a Signature_Block pass validation
 (i.e., all segments are processed and the Signature_Block has not yet
 been marked 'Not Valid'), then the Signature_Block is marked as
 'Valid'.
 If at least one Signature_Block is marked as 'Valid', then the
 validation algorithm terminates and the BGPsec UPDATE message is
 deemed 'Valid'.  (That is, if a BGPsec UPDATE message contains two
 Signature_Blocks, then the UPDATE message is deemed 'Valid' if the
 first Signature_Block is marked 'Valid' OR the second Signature_Block
 is marked 'Valid'.)

6. Algorithms and Extensibility

6.1. Algorithm Suite Considerations

 Note that there is currently no support for bilateral negotiation
 (using BGP capabilities) between BGPsec peers to use a particular
 (digest and signature) algorithm suite.  This is because the
 algorithm suite used by the sender of a BGPsec UPDATE message MUST be
 understood not only by the peer to whom it is directly sending the
 message but also by all BGPsec speakers to whom the route
 advertisement is eventually propagated.  Therefore, selection of an
 algorithm suite cannot be a local matter negotiated by BGP peers but
 instead must be coordinated throughout the Internet.

Lepinski & Sriram Standards Track [Page 27] RFC 8205 BGPsec Protocol September 2017

 To this end, [RFC8208] specifies a mandatory-to-use 'current'
 algorithm suite for use by all BGPsec speakers.
 It is anticipated that, in the future, [RFC8208] or its successor
 will be updated to specify a transition from the 'current' algorithm
 suite to a 'new' algorithm suite.  During the period of transition,
 all BGPsec UPDATE messages SHOULD simultaneously use both the
 'current' algorithm suite and the 'new' algorithm suite.  (Note that
 Sections 3 and 4 specify how the BGPsec_PATH attribute can contain
 signatures, in parallel, for two algorithm suites.)  Once the
 transition is complete, the use of the old 'current' algorithm will
 be deprecated, the use of the 'new' algorithm will be mandatory, and
 a subsequent 'even newer' algorithm suite may be specified as
 "recommended to implement".  Once the transition has successfully
 been completed in this manner, BGPsec speakers SHOULD include only a
 single Signature_Block (corresponding to the 'new' algorithm).

6.2. Considerations for the SKI Size

 Depending on the method of generating key identifiers [RFC7093], the
 size of the SKI in an RPKI router certificate may vary.  The SKI
 field in the BGPsec_PATH attribute has a fixed size of 20 octets (see
 Figure 7).  If the SKI is longer than 20 octets, then use the
 leftmost 20 octets of the SKI (excluding the tag and length)
 [RFC7093].  If the SKI value is shorter than 20 octets, then pad the
 SKI (excluding the tag and length) to the right (least significant
 octets) with octets having "0" values.

6.3. Extensibility Considerations

 This section discusses potential changes to BGPsec that would require
 substantial changes to the processing of the BGPsec_PATH and thus
 necessitate a new version of BGPsec.  Examples of such changes
 include:
 o  A new type of signature algorithm that produces signatures of
    variable length
 o  A new type of signature algorithm for which the number of
    signatures in the Signature_Block is not equal to the number of
    ASes in the Secure_Path (e.g., aggregate signatures)
 o  Changes to the data that is protected by the BGPsec signatures
    (e.g., attributes other than the AS path)
 In the case that such a change to BGPsec were deemed desirable, it is
 expected that a subsequent version of BGPsec would be created and
 that this version of BGPsec would specify a new BGP path attribute --

Lepinski & Sriram Standards Track [Page 28] RFC 8205 BGPsec Protocol September 2017

 let's call it "BGPsec_PATH_Two" -- that is designed to accommodate
 the desired changes to BGPsec.  In such a case, [RFC8208] or its
 successor would be updated to specify algorithm suites appropriate
 for the new version of BGPsec.
 At this point, a transition would begin that is analogous to the
 algorithm transition discussed in Section 6.1.  During the transition
 period, all BGPsec speakers SHOULD simultaneously include both the
 BGPsec_PATH attribute and the new BGPsec_PATH_Two attribute.  Once
 the transition is complete, the use of BGPsec_PATH could then be
 deprecated, at which point BGPsec speakers should include only the
 new BGPsec_PATH_Two attribute.  Such a process could facilitate a
 transition to a new BGPsec semantics in a backwards-compatible
 fashion.

7. Operations and Management Considerations

 Some operations and management issues that are closely relevant to
 BGPsec protocol specification and deployment are highlighted here.
 The best practices concerning operations and deployment of BGPsec are
 provided in [RFC8207].

7.1. Capability Negotiation Failure

 Section 2.2 describes the negotiation required to establish a
 BGPsec-capable peering session.  Not only must the BGPsec capability
 be exchanged (and agreed on), but the BGP multiprotocol extension
 [RFC4760] for the same AFI and the 4-byte AS capability [RFC6793]
 MUST also be exchanged.  Failure to properly negotiate a BGPsec
 session -- due to a missing capability, for example -- may still
 result in the exchange of BGP (unsigned) UPDATE messages.  It is
 RECOMMENDED that an implementation log the failure to properly
 negotiate a BGPsec session.  Also, an implementation MUST have the
 ability to prevent a BGP session from being established if configured
 to only use BGPsec.

7.2. Preventing Misuse of pCount=0

 A peer that is an Internet Exchange Point (IXP) (i.e., route server)
 with a transparent AS is expected to set pCount=0 in its Secure_Path
 Segment while forwarding an UPDATE message to a peer (see
 Section 4.2).  Clearly, such an IXP MUST configure its BGPsec router
 to set pCount=0 in its Secure_Path Segment.  This also means that a
 BGPsec speaker MUST be configured so that it permits pCount=0 from an
 IXP peer.  Two other cases where pCount is set to 0 are in the
 contexts of an AS confederation (see Section 4.3) and of AS migration
 [RFC8206].  In these two cases, pCount=0 is set and accepted within
 the same AS (albeit the AS has two different identities).  Note that

Lepinski & Sriram Standards Track [Page 29] RFC 8205 BGPsec Protocol September 2017

 if a BGPsec speaker does not expect a peer AS to set its pCount=0 and
 if an UPDATE message received from that peer violates this, then the
 UPDATE message MUST be considered to be in error (see the list of
 checks in Section 5.2).  See Section 8.4 for a discussion of security
 considerations concerning pCount=0.

7.3. Early Termination of Signature Verification

 During the validation of a BGPsec UPDATE message, route processor
 performance speedup can be achieved by incorporating the following
 observations.  An UPDATE message is deemed 'Valid' if at least one of
 the Signature_Blocks is marked as 'Valid' (see Section 5.2).
 Therefore, if an UPDATE message contains two Signature_Blocks and the
 first one verified is found 'Valid', then the second Signature_Block
 does not have to be verified.  And if the UPDATE message is chosen
 for best path, then the BGPsec speaker adds its signature (generated
 with the respective algorithm) to each of the two Signature_Blocks
 and forwards the UPDATE message.  Also, a BGPsec UPDATE message is
 deemed 'Not Valid' if at least one signature in each of the
 Signature_Blocks is invalid.  This principle can also be used for
 route processor workload savings, i.e., the verification for a
 Signature_Block terminates early when the first invalid signature is
 encountered.

7.4. Non-deterministic Signature Algorithms

 Many signature algorithms are non-deterministic.  That is, many
 signature algorithms will produce different signatures each time they
 are run (even when they are signing the same data with the same key).
 Therefore, if a BGPsec router receives a BGPsec UPDATE message from a
 peer and later receives a second BGPsec UPDATE message from the same
 peer for the same prefix with the same Secure_Path and SKIs, the
 second UPDATE message MAY differ from the first UPDATE message in the
 signature fields (for a non-deterministic signature algorithm).
 However, the two sets of signature fields will not differ if the
 sender caches and reuses the previous signature.  For a deterministic
 signature algorithm, the signature fields MUST be identical between
 the two UPDATE messages.  On the basis of these observations, an
 implementation MAY incorporate optimizations in update validation
 processing.

7.5. Private AS Numbers

 It is possible that a stub customer of an ISP employs a private AS
 number.  Such a stub customer cannot publish a ROA in the Global RPKI
 for the private AS number and the prefixes that they use.  Also, the
 Global RPKI cannot support private AS numbers (i.e., BGPsec speakers
 in private ASes cannot be issued router certificates in the Global

Lepinski & Sriram Standards Track [Page 30] RFC 8205 BGPsec Protocol September 2017

 RPKI).  For interactions between the stub customer (with the private
 AS number) and the ISP, the following two scenarios are possible:
 1.  The stub customer sends an unsigned BGP UPDATE message for a
     prefix to the ISP's AS.  An edge BGPsec speaker in the ISP's AS
     may choose to propagate the prefix to its non-BGPsec and BGPsec
     peers.  If so, the ISP's edge BGPsec speaker MUST strip the
     AS_PATH with the private AS number and then (a) re-originate the
     prefix without any signatures towards its non-BGPsec peer and
     (b) re-originate the prefix including its own signature towards
     its BGPsec peer.  In both cases (i.e., (a) and (b)), the prefix
     MUST have a ROA in the Global RPKI authorizing the ISP's AS to
     originate it.
 2.  The ISP and the stub customer may use a local RPKI repository
     (using a mechanism such as one of the mechanisms described in
     [SLURM]).  Then, there can be a ROA for the prefix originated by
     the stub AS, and the eBGP speaker in the stub AS can be a BGPsec
     speaker having a router certificate, albeit the ROA and router
     certificate are valid only locally.  With this arrangement, the
     stub AS sends a signed UPDATE message for the prefix to the ISP's
     AS.  An edge BGPsec speaker in the ISP's AS validates the UPDATE
     message, using RPKI data based on the local RPKI view.  Further,
     it may choose to propagate the prefix to its non-BGPsec and
     BGPsec peers.  If so, the ISP's edge BGPsec speaker MUST strip
     the Secure_Path and the Signature Segment received from the stub
     AS with the private AS number and then (a) re-originate the
     prefix without any signatures towards its non-BGPsec peer and
     (b) re-originate the prefix including its own signature towards
     its BGPsec peer.  In both cases (i.e., (a) and (b)), the prefix
     MUST have a ROA in the Global RPKI authorizing the ISP's AS to
     originate it.
 It is possible that private AS numbers are used in an AS
 confederation [RFC5065].  The BGPsec protocol requires that when a
 BGPsec UPDATE message propagates through a confederation, each
 Member-AS that forwards it to a peer Member-AS MUST sign the UPDATE
 message (see Section 4.3).  However, the Global RPKI cannot support
 private AS numbers.  In order for the BGPsec speakers in Member-ASes
 with private AS numbers to have digital certificates, there MUST be a
 mechanism in place in the confederation that allows the establishment
 of a local, customized view of the RPKI, augmenting the Global RPKI
 repository data as needed.  Since this mechanism (for augmenting and
 maintaining a local image of RPKI data) operates locally within an AS
 or AS confederation, it need not be standard based.  However, a
 standard-based mechanism can be used (see [SLURM]).  Recall that in
 order to prevent exposure of the internals of AS confederations, a

Lepinski & Sriram Standards Track [Page 31] RFC 8205 BGPsec Protocol September 2017

 BGPsec speaker exporting to a non-member removes all
 intra-confederation Secure_Path Segments and Signatures (see
 Section 4.3).

7.6. Robustness Considerations for Accessing RPKI Data

 The deployment structure, technologies, and best practices concerning
 Global RPKI data to reach routers (via local RPKI caches) are
 described in [RFC6810], [RFC8210], [RFC8181], [RFC7115], [RFC8207],
 and [RFC8182].  For example, Serial-Number-based incremental update
 mechanisms are used for efficient transfer of just the data records
 that have changed since the last update [RFC6810] [RFC8210].  The
 update notification file is used by Relying Parties (RPs) to discover
 whether any changes exist between the state of the Global RPKI
 repository and the RP's cache [RFC8182].  The notification describes
 the location of (1) the files containing the snapshot and
 (2) incremental deltas, which can be used by the RP to synchronize
 with the repository.  Making use of these technologies and best
 practices results in enabling robustness, efficiency, and better
 security for the BGPsec routers and RPKI caches in terms of the flow
 of RPKI data from repositories to RPKI caches to routers.  With these
 mechanisms, it is believed that an attacker wouldn't be able to
 meaningfully correlate RPKI data flows with BGPsec RP (or router)
 actions, thus avoiding attacks that may attempt to determine the set
 of ASes interacting with an RP via the interactions between the RP
 and RPKI servers.

7.7. Graceful Restart

 During Graceful Restart (GR), restarting and receiving BGPsec
 speakers MUST follow the procedures specified in [RFC4724] for
 restarting and receiving BGP speakers, respectively.  In particular,
 the behavior of retaining the forwarding state for the routes in the
 Loc-RIB [RFC4271] and marking them as stale, as well as not
 differentiating between stale routing information and other
 information during forwarding, will be the same as the behavior
 specified in [RFC4724].

7.8. Robustness of Secret Random Number in ECDSA

 The Elliptic Curve Digital Signature Algorithm (ECDSA) with curve
 P-256 is used for signing UPDATE messages in BGPsec [RFC8208].  For
 ECDSA, it is stated in Section 6.3 of [FIPS186-4] that a new secret
 random number "k" shall be generated prior to the generation of each
 digital signature.  A high-entropy random bit generator (RBG) must be
 used for generating "k", and any potential bias in the "k" generation
 algorithm must be mitigated (see the methods described in [FIPS186-4]
 and [SP800-90A]).

Lepinski & Sriram Standards Track [Page 32] RFC 8205 BGPsec Protocol September 2017

7.9. Incremental/Partial Deployment Considerations

 What will migration from BGP to BGPsec look like?  What are the
 benefits for the first adopters?  Initially, small groups of
 contiguous ASes would be doing BGPsec.  There would possibly be one
 or more such groups in different geographic regions of the global
 Internet.  Only the routes originated within each group and
 propagated within its borders would get the benefits of cryptographic
 AS path protection.  As BGPsec adoption grows, each group grows in
 size, and eventually they join together to form even larger
 BGPsec-capable groups of contiguous ASes.  The benefit for early
 adopters starts with AS path security within the regions of
 contiguous ASes spanned by their respective groups.  Over time, they
 would see those regions of contiguous ASes grow much larger.
 During partial deployment, if an AS in the path doesn't support
 BGPsec, then BGP goes back to traditional mode, i.e., BGPsec UPDATE
 messages are converted to unsigned UPDATE messages before forwarding
 to that AS (see Section 4.4).  At this point, the assurance that the
 UPDATE message propagated via the sequence of ASes listed is lost.
 In other words, for the BGPsec routers residing in the ASes starting
 from the origin AS to the AS before the one not supporting BGPsec,
 the assurance can still be provided, but not beyond that (for the
 UPDATE messages in consideration).

8. Security Considerations

 For a discussion of the BGPsec threat model and related security
 considerations, please see RFC 7132 [RFC7132].

8.1. Security Guarantees

 When used in conjunction with origin validation (see RFC 6483
 [RFC6483] and RFC 6811 [RFC6811]), a BGPsec speaker who receives a
 valid BGPsec UPDATE message containing a route advertisement for a
 given prefix is provided with the following security guarantees:
 o  The origin AS number corresponds to an AS that has been
    authorized, in the RPKI, by the IP address space holder to
    originate route advertisements for the given prefix.
 o  For each AS in the path, a BGPsec speaker authorized by the holder
    of the AS number intentionally chose (in accordance with local
    policy) to propagate the route advertisement to the subsequent AS
    in the path.

Lepinski & Sriram Standards Track [Page 33] RFC 8205 BGPsec Protocol September 2017

 That is, the recipient of a valid BGPsec UPDATE message is assured
 that the UPDATE message propagated via the sequence of ASes listed in
 the Secure_Path portion of the BGPsec_PATH attribute.  (It should be
 noted that BGPsec does not offer any guarantee that the data packets
 would flow along the indicated path; it only guarantees that the BGP
 UPDATE message conveying the path indeed propagated along the
 indicated path.)  Furthermore, the recipient is assured that this
 path terminates in an AS that has been authorized by the IP address
 space holder as a legitimate destination for traffic to the given
 prefix.
 Note that although BGPsec provides a mechanism for an AS to validate
 that a received UPDATE message has certain security properties, the
 use of such a mechanism to influence route selection is completely a
 matter of local policy.  Therefore, a BGPsec speaker can make no
 assumptions about the validity of a route received from an external
 (eBGP) BGPsec peer.  That is, a compliant BGPsec peer may (depending
 on the local policy of the peer) send UPDATE messages that fail the
 validity test in Section 5.  Thus, a BGPsec speaker MUST completely
 validate all BGPsec UPDATE messages received from external peers.
 (Validation of UPDATE messages received from internal peers is also a
 matter of local policy; see Section 5.)

8.2. On the Removal of BGPsec Signatures

 There may be cases where a BGPsec speaker deems 'Valid' (as per the
 validation algorithm in Section 5.2) a BGPsec UPDATE message that
 contains both a 'Valid' and a 'Not Valid' Signature_Block.  That is,
 the UPDATE message contains two sets of signatures corresponding to
 two algorithm suites, and one set of signatures verifies correctly
 and the other set of signatures fails to verify.  In this case, the
 protocol specifies that a BGPsec speaker choosing to propagate the
 route advertisement in such an UPDATE message MUST add its signature
 to each of the Signature_Blocks (see Section 4.2).  Thus, the BGPsec
 speaker creates a signature using both algorithm suites and creates a
 new UPDATE message that contains both the 'Valid' and the 'Not Valid'
 set of signatures (from its own vantage point).
 To understand the reason for such a design decision, consider the
 case where the BGPsec speaker receives an UPDATE message with both a
 set of algorithm A signatures that are 'Valid' and a set of algorithm
 B signatures that are 'Not Valid'.  In such a case, it is possible
 (perhaps even likely, depending on the state of the algorithm
 transition) that some of the BGPsec speaker's peers (or other
 entities further downstream in the BGP topology) do not support
 algorithm A.  Therefore, if the BGPsec speaker were to remove the
 'Not Valid' set of signatures corresponding to algorithm B, such
 entities would treat the message as though it were unsigned.  By

Lepinski & Sriram Standards Track [Page 34] RFC 8205 BGPsec Protocol September 2017

 including the 'Not Valid' set of signatures when propagating a route
 advertisement, the BGPsec speaker ensures that downstream entities
 have as much information as possible to make an informed opinion
 about the validation status of a BGPsec UPDATE message.
 Note also that during a period of partial BGPsec deployment, a
 downstream entity might reasonably treat unsigned messages
 differently from BGPsec UPDATE messages that contain a single set of
 'Not Valid' signatures.  That is, by removing the set of 'Not Valid'
 signatures, the BGPsec speaker might actually cause a downstream
 entity to 'upgrade' the status of a route advertisement from
 'Not Valid' to unsigned.  Finally, note that in the above scenario,
 the BGPsec speaker might have deemed algorithm A signatures 'Valid'
 only because of some issue with the RPKI state local to its AS (for
 example, its AS might not yet have obtained a Certificate Revocation
 List (CRL) indicating that a key used to verify an algorithm A
 signature belongs to a newly revoked certificate).  In such a case,
 it is highly desirable for a downstream entity to treat the UPDATE
 message as 'Not Valid' (due to the revocation) and not as 'unsigned'
 (which would happen if the 'Not Valid' Signature_Blocks were removed
 en route).
 A similar argument applies to the case where a BGPsec speaker (for
 some reason, such as a lack of viable alternatives) selects as its
 best path (to a given prefix) a route obtained via a 'Not Valid'
 BGPsec UPDATE message.  In such a case, the BGPsec speaker should
 propagate a signed BGPsec UPDATE message, adding its signature to the
 'Not Valid' signatures that already exist.  Again, this is to ensure
 that downstream entities are able to make an informed decision and
 not erroneously treat the route as unsigned.  It should also be noted
 that due to possible differences in RPKI data observed at different
 vantage points in the network, a BGPsec UPDATE message deemed 'Not
 Valid' at an upstream BGPsec speaker may be deemed 'Valid' by another
 BGP speaker downstream.
 Indeed, when a BGPsec speaker signs an outgoing UPDATE message, it is
 not attesting to a belief that all signatures prior to its own
 signature are valid.  Instead, it is merely asserting that:
 o  The BGPsec speaker received the given route advertisement with the
    indicated prefix, AFI, SAFI, and Secure_Path, and
 o  The BGPsec speaker chose to propagate an advertisement for this
    route to the peer (implicitly) indicated by the 'Target AS
    Number'.

Lepinski & Sriram Standards Track [Page 35] RFC 8205 BGPsec Protocol September 2017

8.3. Mitigation of Denial-of-Service Attacks

 The BGPsec update validation procedure is a potential target for
 denial-of-service attacks against a BGPsec speaker.  The mitigation
 of denial-of-service attacks that are specific to the BGPsec protocol
 is considered here.
 To mitigate the effectiveness of such denial-of-service attacks,
 BGPsec speakers should implement an update validation algorithm that
 performs expensive checks (e.g., signature verification) after
 performing checks that are less expensive (e.g., syntax checks).  The
 validation algorithm specified in Section 5.2 was chosen so as to
 perform checks that are likely to be expensive after checks that are
 likely to be inexpensive.  However, the relative cost of performing
 required validation steps may vary between implementations, and thus
 the algorithm specified in Section 5.2 may not provide the best
 denial-of-service protection for all implementations.
 Additionally, sending UPDATE messages with very long AS paths (and
 hence a large number of signatures) is a potential mechanism to
 conduct denial-of-service attacks.  For this reason, it is important
 that an implementation of the validation algorithm stops attempting
 to verify signatures as soon as an invalid signature is found.  (This
 ensures that long sequences of invalid signatures cannot be used for
 denial-of-service attacks.)  Furthermore, implementations can
 mitigate such attacks by only performing validation on UPDATE
 messages that, if valid, would be selected as the best path.  That
 is, if an UPDATE message contains a route that would lose out in best
 path selection for other reasons (e.g., a very long AS path), then it
 is not necessary to determine the BGPsec-validity status of the
 route.

8.4. Additional Security Considerations

 The mechanism of setting the pCount field to 0 is included in this
 specification to enable route servers in the control path to
 participate in BGPsec without increasing the length of the AS path.
 Two other scenarios where pCount=0 is utilized are in the contexts of
 an AS confederation (see Section 4.3) and of AS migration [RFC8206].
 In these two scenarios, pCount=0 is set and also accepted within the
 same AS (albeit the AS has two different identities).  However,
 entities other than route servers, confederation ASes, or migrating
 ASes could conceivably use this mechanism (set the pCount to 0) to
 attract traffic (by reducing the length of the AS path)
 illegitimately.  This risk is largely mitigated if every BGPsec
 speaker follows the operational guidance in Section 7.2 for
 configuration for setting pCount=0 and/or accepting pCount=0 from a
 peer.  However, note that a recipient of a BGPsec UPDATE message

Lepinski & Sriram Standards Track [Page 36] RFC 8205 BGPsec Protocol September 2017

 within which an upstream entity two or more hops away has set pCount
 to 0 is unable to verify for themselves whether pCount was set to 0
 legitimately.
 There is a possibility of passing a BGPsec UPDATE message via
 tunneling between colluding ASes.  For example, let's say that AS-X
 does not peer with AS-Y but colludes with AS-Y, and it signs and
 sends a BGPsec UPDATE message to AS-Y by tunneling.  AS-Y can then
 further sign and propagate the BGPsec UPDATE message to its peers.
 It is beyond the scope of the BGPsec protocol to detect this form of
 malicious behavior.  BGPsec is designed to protect messages sent
 within BGP (i.e., within the control plane) -- not when the control
 plane is bypassed.
 A variant of the collusion by tunneling mentioned above can happen in
 the context of AS confederations.  When a BGPsec router (outside of a
 confederation) is forwarding an UPDATE message to a Member-AS in the
 confederation, it signs the UPDATE message to the public AS number of
 the confederation and not to the member's AS number (see
 Section 4.3).  The Member-AS can tunnel the signed UPDATE message to
 another Member-AS as received (i.e., without adding a signature).
 The UPDATE message can then be propagated using BGPsec to other
 confederation members or to BGPsec neighbors outside of the
 confederation.  This kind of operation is possible, but no grave
 security or reachability compromise is feared for the following
 reasons:
 o  The confederation members belong to one organization, and strong
    internal trust is expected.
 o  Recall that the signatures that are internal to the confederation
    MUST be removed prior to forwarding the UPDATE message to an
    outside BGPsec router (see Section 4.3).
 BGPsec does not provide protection against attacks at the transport
 layer.  As with any BGP session, an adversary on the path between a
 BGPsec speaker and its peer is able to perform attacks such as
 modifying valid BGPsec UPDATE messages to cause them to fail
 validation, injecting (unsigned) BGP UPDATE messages without
 BGPsec_PATH attributes, injecting BGPsec UPDATE messages with
 BGPsec_PATH attributes that fail validation, or causing the peer to
 tear down the BGP session.  The use of BGPsec does nothing to
 increase the power of an on-path adversary -- in particular, even an
 on-path adversary cannot cause a BGPsec speaker to believe that a
 BGPsec-invalid route is valid.  However, as with any BGP session,
 BGPsec sessions SHOULD be protected by appropriate transport security
 mechanisms (see the Security Considerations section in [RFC4271]).

Lepinski & Sriram Standards Track [Page 37] RFC 8205 BGPsec Protocol September 2017

 There is a possibility of replay attacks, defined as follows.  In the
 context of BGPsec, a replay attack occurs when a malicious BGPsec
 speaker in the AS path suppresses a prefix withdrawal (implicit or
 explicit).  Further, a replay attack is said to occur also when a
 malicious BGPsec speaker replays a previously received BGPsec
 announcement for a prefix that has since been withdrawn.  The
 mitigation strategy for replay attacks involves router certificate
 rollover; please see [ROLLOVER] for details.

9. IANA Considerations

 IANA has registered a new BGP capability described in Section 2.1 in
 the "Capability Codes" registry's "IETF Review" range [RFC8126].  The
 description for the new capability is "BGPsec Capability".  This
 document is the reference for the new capability.
 IANA has also registered a new path attribute described in Section 3
 in the "BGP Path Attributes" registry.  The code for this new
 attribute is "BGPsec_PATH".  This document is the reference for the
 new attribute.
 IANA has defined the "BGPsec Capability" registry in the "Resource
 Public Key Infrastructure (RPKI)" group.  The registry is as shown in
 Figure 10, with values assigned from Section 2.1:
      +------+------------------------------------+------------+
      | Bits | Field                              | Reference  |
      +------+------------------------------------+------------+
      | 0-3  | Version                            | [RFC8205]  |
      |      | Value = 0x0                        |            |
      +------+------------------------------------+------------+
      | 4    | Direction                          | [RFC8205]  |
      |      |(Both possible values 0 and 1 are   |            |
      |      | fully specified by this RFC)       |            |
      +------+------------------------------------+------------+
      | 5-7  | Unassigned                         | [RFC8205]  |
      |      | Value = 000 (in binary)            |            |
      +------+------------------------------------+------------+
            Figure 10: IANA Registry for BGPsec Capability
 The Direction bit (fourth bit) has a value of either 0 or 1, and both
 values are fully specified by this document.  Future Version values
 and future values of the Unassigned bits are assigned using the
 "Standards Action" registration procedures defined in RFC 8126
 [RFC8126].

Lepinski & Sriram Standards Track [Page 38] RFC 8205 BGPsec Protocol September 2017

 IANA has defined the "BGPsec_PATH Flags" registry in the "Resource
 Public Key Infrastructure (RPKI)" group.  The registry is as shown in
 Figure 11, with one value assigned from Section 3.1:
   +------+-------------------------------------------+------------+
   | Flag | Description                               | Reference  |
   +------+-------------------------------------------+------------+
   | 0    | Confed_Segment                            | [RFC8205]  |
   |      | Bit value = 1 means Flag set              |            |
   |      |                (indicates Confed_Segment) |            |
   |      | Bit value = 0 is default                  |            |
   +------+-------------------------------------------+------------+
   | 1-7  | Unassigned                                | [RFC8205]  |
   |      | Value: All 7 bits set to zero             |            |
   +------+-------------------------------------------+------------+
         Figure 11: IANA Registry for BGPsec_PATH Flags Field
 Future values of the Unassigned bits are assigned using the
 "Standards Action" registration procedures defined in RFC 8126
 [RFC8126].

10. References

10.1. Normative References

 [IANA-AF]  IANA, "Address Family Numbers",
            <https://www.iana.org/assignments/address-family-numbers>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <https://www.rfc-editor.org/info/rfc2119>.
 [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
            Border Gateway Protocol 4 (BGP-4)", RFC 4271,
            DOI 10.17487/RFC4271, January 2006,
            <https://www.rfc-editor.org/info/rfc4271>.
 [RFC4724]  Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y.
            Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724,
            DOI 10.17487/RFC4724, January 2007,
            <https://www.rfc-editor.org/info/rfc4724>.
 [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
            "Multiprotocol Extensions for BGP-4", RFC 4760,
            DOI 10.17487/RFC4760, January 2007,
            <https://www.rfc-editor.org/info/rfc4760>.

Lepinski & Sriram Standards Track [Page 39] RFC 8205 BGPsec Protocol September 2017

 [RFC5065]  Traina, P., McPherson, D., and J. Scudder, "Autonomous
            System Confederations for BGP", RFC 5065,
            DOI 10.17487/RFC5065, August 2007,
            <https://www.rfc-editor.org/info/rfc5065>.
 [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
            with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
            2009, <https://www.rfc-editor.org/info/rfc5492>.
 [RFC6482]  Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
            Origin Authorizations (ROAs)", RFC 6482,
            DOI 10.17487/RFC6482, February 2012,
            <https://www.rfc-editor.org/info/rfc6482>.
 [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
            X.509 PKIX Resource Certificates", RFC 6487,
            DOI 10.17487/RFC6487, February 2012,
            <https://www.rfc-editor.org/info/rfc6487>.
 [RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
            Autonomous System (AS) Number Space", RFC 6793,
            DOI 10.17487/RFC6793, December 2012,
            <https://www.rfc-editor.org/info/rfc6793>.
 [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
            Patel, "Revised Error Handling for BGP UPDATE Messages",
            RFC 7606, DOI 10.17487/RFC7606, August 2015,
            <https://www.rfc-editor.org/info/rfc7606>.
 [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
            Writing an IANA Considerations Section in RFCs", BCP 26,
            RFC 8126, DOI 10.17487/RFC8126, June 2017,
            <https://www.rfc-editor.org/info/rfc8126>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <https://www.rfc-editor.org/info/rfc8174>.
 [RFC8208]  Turner, S. and O. Borchert, "BGPsec Algorithms, Key
            Formats, and Signature Formats", RFC 8208,
            DOI 10.17487/RFC8208, September 2017,
            <https://www.rfc-editor.org/info/rfc8208>.
 [RFC8209]  Reynolds, M., Turner, S., and S. Kent, "A Profile for
            BGPsec Router Certificates, Certificate Revocation Lists,
            and Certification Requests", RFC 8209,
            DOI 10.17487/RFC8209, September 2017,
            <https://www.rfc-editor.org/info/rfc8209>.

Lepinski & Sriram Standards Track [Page 40] RFC 8205 BGPsec Protocol September 2017

10.2. Informative References

 [Borchert] Borchert, O. and M. Baer, "Subject: Modification request:
            draft-ietf-sidr-bgpsec-protocol-14", message to the IETF
            SIDR WG Mailing List, 10 February 2016,
            <https://mailarchive.ietf.org/arch/msg/
            sidr/8B_e4CNxQCUKeZ_AUzsdnn2f5Mu>.
 [FIPS186-4]
            National Institute of Standards and Technology, "Digital
            Signature Standard (DSS)", NIST FIPS Publication
            186-4, DOI 10.6028/NIST.FIPS.186-4, July 2013,
            <http://nvlpubs.nist.gov/nistpubs/FIPS/
            NIST.FIPS.186-4.pdf>.
 [RFC6472]  Kumari, W. and K. Sriram, "Recommendation for Not Using
            AS_SET and AS_CONFED_SET in BGP", BCP 172, RFC 6472,
            DOI 10.17487/RFC6472, December 2011,
            <https://www.rfc-editor.org/info/rfc6472>.
 [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
            Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
            February 2012, <https://www.rfc-editor.org/info/rfc6480>.
 [RFC6483]  Huston, G. and G. Michaelson, "Validation of Route
            Origination Using the Resource Certificate Public Key
            Infrastructure (PKI) and Route Origin Authorizations
            (ROAs)", RFC 6483, DOI 10.17487/RFC6483, February 2012,
            <https://www.rfc-editor.org/info/rfc6483>.
 [RFC6810]  Bush, R. and R. Austein, "The Resource Public Key
            Infrastructure (RPKI) to Router Protocol", RFC 6810,
            DOI 10.17487/RFC6810, January 2013,
            <https://www.rfc-editor.org/info/rfc6810>.
 [RFC6811]  Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
            Austein, "BGP Prefix Origin Validation", RFC 6811,
            DOI 10.17487/RFC6811, January 2013,
            <https://www.rfc-editor.org/info/rfc6811>.
 [RFC7093]  Turner, S., Kent, S., and J. Manger, "Additional Methods
            for Generating Key Identifiers Values", RFC 7093,
            DOI 10.17487/RFC7093, December 2013,
            <https://www.rfc-editor.org/info/rfc7093>.

Lepinski & Sriram Standards Track [Page 41] RFC 8205 BGPsec Protocol September 2017

 [RFC7115]  Bush, R., "Origin Validation Operation Based on the
            Resource Public Key Infrastructure (RPKI)", BCP 185,
            RFC 7115, DOI 10.17487/RFC7115, January 2014,
            <https://www.rfc-editor.org/info/rfc7115>.
 [RFC7132]  Kent, S. and A. Chi, "Threat Model for BGP Path Security",
            RFC 7132, DOI 10.17487/RFC7132, February 2014,
            <https://www.rfc-editor.org/info/rfc7132>.
 [RFC8181]  Weiler, S., Sonalker, A., and R. Austein, "A Publication
            Protocol for the Resource Public Key Infrastructure
            (RPKI)", July 2017,
            <https://www.rfc-editor.org/info/rfc8181>.
 [RFC8182]  Bruijnzeels, T., Muravskiy, O., Weber, B., and R. Austein,
            "The RPKI Repository Delta Protocol (RRDP)", RFC 8182,
            DOI 10.17487/RFC8182, July 2017,
            <https://www.rfc-editor.org/info/rfc8182>.
 [RFC8206]  George, W. and S. Murphy, "BGPsec Considerations for
            Autonomous System (AS) Migration", RFC 8206,
            DOI 10.17487/RFC8206, September 2017,
            <https://www.rfc-editor.org/info/rfc8206>.
 [RFC8207]  Bush, R., "BGPsec Operational Considerations", BCP 211,
            RFC 8207, DOI 10.17487/RFC8207, September 2017,
            <https://www.rfc-editor.org/info/rfc8207>.
 [RFC8210]  Bush, R. and R. Austein, "The Resource Public Key
            Infrastructure (RPKI) to Router Protocol, Version 1",
            RFC 8210, DOI 10.17487/RFC8210, September 2017,
            <https://www.rfc-editor.org/info/rfc8210>.
 [ROLLOVER] Weis, B., Gagliano, R., and K. Patel, "BGPsec Router
            Certificate Rollover", Work in Progress,
            draft-ietf-sidrops-bgpsec-rollover-01, August 2017.
 [SLURM]    Mandelberg, D., Ma, D., and T. Bruijnzeels, "Simplified
            Local internet nUmber Resource Management with the RPKI",
            Work in Progress, draft-ietf-sidr-slurm-04, March 2017.
 [SP800-90A]
            National Institute of Standards and Technology,
            "Recommendation for Random Number Generation Using
            Deterministic Random Bit Generators", NIST SP 800-90A
            Rev 1, DOI 10.6028/NIST.SP.800-90Ar1, June 2015,
            <http://nvlpubs.nist.gov/nistpubs/SpecialPublications/
            NIST.SP.800-90Ar1.pdf>.

Lepinski & Sriram Standards Track [Page 42] RFC 8205 BGPsec Protocol September 2017

Acknowledgements

 The authors would like to thank Michael Baer, Oliver Borchert, David
 Mandelberg, Mehmet Adalier, Sean Turner, Wes George, Jeff Haas,
 Alvaro Retana, Nevil Brownlee, Matthias Waehlisch, Tim Polk, Russ
 Mundy, Wes Hardaker, Sharon Goldberg, Ed Kern, Doug Maughan, Pradosh
 Mohapatra, Mark Reynolds, Heather Schiller, Jason Schiller, Ruediger
 Volk, and David Ward for their review, comments, and suggestions
 during the course of this work.  Thanks are also due to many IESG
 reviewers whose comments greatly helped improve the clarity,
 accuracy, and presentation in the document.
 The authors particularly wish to acknowledge Oliver Borchert and
 Michael Baer for their review and suggestions [Borchert] concerning
 the sequence of octets to be hashed (Figures 8 and 9 in Sections 4.2
 and 5.2, respectively).  This was an important contribution based on
 their implementation experience.

Lepinski & Sriram Standards Track [Page 43] RFC 8205 BGPsec Protocol September 2017

Contributors

 The following people have made significant contributions to this
 document and should be considered co-authors:
 Rob Austein
 Dragon Research Labs
 Email: sra@hactrn.net
 Steven Bellovin
 Columbia University
 Email: smb@cs.columbia.edu
 Russ Housley
 Vigil Security
 Email: housley@vigilsec.com
 Stephen Kent
 BBN Technologies
 Email: kent@alum.mit.edu
 Warren Kumari
 Google
 Email: warren@kumari.net
 Doug Montgomery
 USA National Institute of Standards and Technology
 Email: dougm@nist.gov
 Chris Morrow
 Google, Inc.
 Email: morrowc@google.com
 Sandy Murphy
 SPARTA, Inc., a Parsons Company
 Email: sandy@tislabs.com
 Keyur Patel
 Arrcus
 Email: keyur@arrcus.com
 John Scudder
 Juniper Networks
 Email: jgs@juniper.net
 Samuel Weiler
 W3C/MIT
 Email: weiler@csail.mit.edu

Lepinski & Sriram Standards Track [Page 44] RFC 8205 BGPsec Protocol September 2017

Authors' Addresses

 Matthew Lepinski (editor)
 New College of Florida
 5800 Bay Shore Road
 Sarasota, FL  34243
 United States of America
 Email: mlepinski@ncf.edu
 Kotikalapudi Sriram (editor)
 USA National Institute of Standards and Technology
 100 Bureau Drive
 Gaithersburg, MD  20899
 United States of America
 Email: kotikalapudi.sriram@nist.gov

Lepinski & Sriram Standards Track [Page 45]

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