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rfc:rfc8061

Internet Engineering Task Force (IETF) D. Farinacci Request for Comments: 8061 lispers.net Category: Experimental B. Weis ISSN: 2070-1721 Cisco Systems

                                                         February 2017
  Locator/ID Separation Protocol (LISP) Data-Plane Confidentiality

Abstract

 This document describes a mechanism for encrypting traffic
 encapsulated using the Locator/ID Separation Protocol (LISP).  The
 design describes how key exchange is achieved using existing LISP
 control-plane mechanisms as well as how to secure the LISP data plane
 from third-party surveillance attacks.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for examination, experimental implementation, and
 evaluation.
 This document defines an Experimental Protocol for the Internet
 community.  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).  Not
 all documents approved by the IESG are a candidate for any level of
 Internet Standard; see 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
 http://www.rfc-editor.org/info/rfc8061.

Farinacci & Weis Experimental [Page 1] RFC 8061 LISP Data-Plane Confidentiality February 2017

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
 (http://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.

Table of Contents

 1. Introduction ....................................................3
 2. Requirements Notation ...........................................4
 3. Definition of Terms .............................................4
 4. Overview ........................................................4
 5. Diffie-Hellman Key Exchange .....................................5
 6. Encoding and Transmitting Key Material ..........................6
 7. Shared Keys Used for the Data Plane .............................8
 8. Data-Plane Operation ...........................................10
 9. Procedures for Encryption and Decryption .......................11
 10. Dynamic Rekeying ..............................................12
 11. Future Work ...................................................13
 12. Security Considerations .......................................14
    12.1. SAAG Support .............................................14
    12.2. LISP-Crypto Security Threats .............................14
 13. IANA Considerations ...........................................15
 14. References ....................................................16
    14.1. Normative References .....................................16
    14.2. Informative References ...................................17
 Acknowledgments ...................................................18
 Authors' Addresses ................................................18

Farinacci & Weis Experimental [Page 2] RFC 8061 LISP Data-Plane Confidentiality February 2017

1. Introduction

 This document describes a mechanism for encrypting LISP-encapsulated
 traffic.  The design describes how key exchange is achieved using
 existing LISP control-plane mechanisms as well as how to secure the
 LISP data plane from third-party surveillance attacks.
 The Locator/ID Separation Protocol [RFC6830] defines a set of
 functions for routers to exchange information used to map from
 non-routable Endpoint Identifiers (EIDs) to routable Routing Locators
 (RLOCs).  LISP Ingress Tunnel Routers (ITRs) and Proxy Ingress Tunnel
 Routers (PITRs) encapsulate packets to Egress Tunnel Routers (ETRs)
 and Re-encapsulating Tunnel Routers (RTRs).  Packets that arrive at
 the ITR or PITR may not be encrypted, which means no protection or
 privacy of the data is added.  When the source host encrypts the data
 stream, encapsulated packets do not need to be encrypted by LISP.
 However, when plaintext packets are sent by hosts, this design can
 encrypt the user payload to maintain privacy on the path between the
 encapsulator (the ITR or PITR) to a decapsulator (ETR or RTR).  The
 encrypted payload is unidirectional.  However, return traffic uses
 the same procedures but with different key values by the same xTRs or
 potentially different xTRs when the paths between LISP sites are
 asymmetric.
 This document has the following requirements (as well as the general
 requirements from [RFC6973]) for the solution space:
 o  Do not require a separate Public Key Infrastructure (PKI) that is
    out of scope of the LISP control-plane architecture.
 o  The budget for key exchange MUST be one round-trip time.  That is,
    only a two-packet exchange can occur.
 o  Use symmetric keying so faster cryptography can be performed in
    the LISP data plane.
 o  Avoid a third-party trust anchor if possible.
 o  Provide for rekeying when secret keys are compromised.
 o  Support Authenticated Encryption with packet integrity checks.
 o  Support multiple Cipher Suites so new crypto algorithms can be
    easily introduced.

Farinacci & Weis Experimental [Page 3] RFC 8061 LISP Data-Plane Confidentiality February 2017

 Satisfying the above requirements provides the following benefits:
 o  Avoiding a PKI reduces the operational cost of managing a secure
    network.  Key management is distributed and independent from any
    other infrastructure.
 o  Packet transport is optimized due to fewer packet headers.  Packet
    loss is reduced by a more efficient key exchange.
 o  Authentication and privacy are provided with a single mechanism
    thereby providing less per-packet overhead and therefore more
    resource efficiency.

2. Requirements Notation

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].

3. Definition of Terms

 AEAD: Authenticated Encryption with Associated Data [RFC5116]
 ICV: Integrity Check Value
 LCAF: LISP Canonical Address Format [RFC8060]
 xTR: A general reference to ITRs, ETRs, RTRs, and PxTRs

4. Overview

 The approach proposed in this document is NOT to rely on the LISP
 mapping system (or any other key-infrastructure system) to store
 security keys.  This will provide for a simpler and more secure
 mechanism.  Secret shared keys will be negotiated between the ITR and
 the ETR in Map-Request and Map-Reply messages.  Therefore, when an
 ITR needs to obtain the RLOC of an ETR, it will get security material
 to compute a shared secret with the ETR.
 The ITR can compute three shared secrets per ETR the ITR is
 encapsulating to.  When the ITR encrypts a packet before
 encapsulation, it will identify the key it used for the crypto
 calculation so the ETR knows which key to use for decrypting the
 packet after decapsulation.  By using key-ids in the LISP header, we
 can also get fast rekeying functionality.
 The key management described in this document is unidirectional from
 the ITR (the encapsulator) to the ETR (the decapsultor).

Farinacci & Weis Experimental [Page 4] RFC 8061 LISP Data-Plane Confidentiality February 2017

5. Diffie-Hellman Key Exchange

 LISP will use a Diffie-Hellman [RFC2631] key exchange sequence and
 computation for computing a shared secret.  The Diffie-Hellman
 parameters will be passed via Cipher Suite code-points in Map-Request
 and Map-Reply messages.
 Here is a brief description how Diffie-Hellman works:
 +----------------------------+---------+----------------------------+
 |              ITR           |         |           ETR              |
 +------+--------+------------+---------+------------+---------------+
 |Secret| Public | Calculates |  Sends  | Calculates | Public |Secret|
 +------|--------|------------|---------|------------|--------|------+
 |  i   |  p,g   |            | p,g --> |            |        |  e   |
 +------|--------|------------|---------|------------|--------|------+
 |  i   | p,g,I  |g^i mod p=I |  I -->  |            | p,g,I  |  e   |
 +------|--------|------------|---------|------------|--------|------+
 |  i   | p,g,I  |            |  <-- E  |g^e mod p=E |  p,g   |  e   |
 +------|--------|------------|---------|------------|--------|------+
 | i,s  |p,g,I,E |E^i mod p=s |         |I^e mod p=s |p,g,I,E | e,s  |
 +------|--------|------------|---------|------------|--------|------+
      Public-Key Exchange for Computing a Shared Private Key [DH]
 Diffie-Hellman parameters 'p' and 'g' must be the same values used by
 the ITR and ETR.  The ITR computes public key 'I' and transmits 'I'
 in a Map-Request packet.  When the ETR receives the Map-Request, it
 uses parameters 'p' and 'g' to compute the ETR's public key 'E'.  The
 ETR transmits 'E' in a Map-Reply message.  At this point, the ETR has
 enough information to compute 's', the shared secret, by using 'I' as
 the base and the ETR's private key 'e' as the exponent.  When the ITR
 receives the Map-Reply, it uses the ETR's public key 'E' with the
 ITR's private key 'i' to compute the same 's' shared secret the ETR
 computed.  The value 'p' is used as a modulus to create the width of
 the shared secret 's' (see Section 6).

Farinacci & Weis Experimental [Page 5] RFC 8061 LISP Data-Plane Confidentiality February 2017

6. Encoding and Transmitting Key Material

 The Diffie-Hellman key material is transmitted in Map-Request and
 Map-Reply messages.  Diffie-Hellman parameters are encoded in the
 LISP Security Key LCAF Type [RFC8060].
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           AFI = 16387         |     Rsvd1     |     Flags     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   Type = 11   |      Rsvd2    |             6 + n             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   Key Count   |      Rsvd3    | Cipher Suite  |   Rsvd4     |R|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Key Length          |     Public Key Material ...   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    ... Public Key Material                    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |              AFI = x          |       Locator Address ...     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Cipher Suite Field Contains DH Key Exchange and Cipher/Hash Functions
 The Key Count field encodes the number of {'Key-Length',
 'Key-Material'} fields included in the encoded LCAF.  The maximum
 number of keys that can be encoded is three, each identified by
 key-id 1, followed by key-id 2, and finally key-id 3.
 The R bit is not used for this use case of the Security Key LCAF Type
 but is reserved for [LISP-DDT] security.  Therefore, the R bit SHOULD
 be transmitted as 0 and MUST be ignored on receipt.

Farinacci & Weis Experimental [Page 6] RFC 8061 LISP Data-Plane Confidentiality February 2017

Cipher Suite 0:

  Reserved

Cipher Suite 1 (LISP_2048MODP_AES128_CBC_SHA256):

  Diffie-Hellman Group: 2048-bit MODP [RFC3526]
  Encryption:  AES with 128-bit keys in CBC mode [AES-CBC]
  Integrity:   Integrated with AEAD_AES_128_CBC_HMAC_SHA_256 [AES-CBC]
  IV length:   16 bytes
  KDF:         HMAC-SHA-256

Cipher Suite 2 (LISP_EC25519_AES128_CBC_SHA256):

  Diffie-Hellman Group: 256-bit Elliptic-Curve 25519 [CURVE25519]
  Encryption:  AES with 128-bit keys in CBC mode [AES-CBC]
  Integrity:   Integrated with AEAD_AES_128_CBC_HMAC_SHA_256 [AES-CBC]
  IV length:   16 bytes
  KDF:         HMAC-SHA-256

Cipher Suite 3 (LISP_2048MODP_AES128_GCM):

  Diffie-Hellman Group: 2048-bit MODP [RFC3526]
  Encryption:  AES with 128-bit keys in GCM mode [RFC5116]
  Integrity:   Integrated with AEAD_AES_128_GCM [RFC5116]
  IV length:   12 bytes
  KDF:         HMAC-SHA-256

Cipher Suite 4 (LISP_3072MODP_AES128_GCM):

  Diffie-Hellman Group: 3072-bit MODP [RFC3526]
  Encryption:  AES with 128-bit keys in GCM mode [RFC5116]
  Integrity:   Integrated with AEAD_AES_128_GCM [RFC5116]
  IV length:   12 bytes
  KDF:         HMAC-SHA-256

Cipher Suite 5 (LISP_256_EC25519_AES128_GCM):

  Diffie-Hellman Group: 256-bit Elliptic-Curve 25519 [CURVE25519]
  Encryption:  AES with 128-bit keys in GCM mode [RFC5116]
  Integrity:   Integrated with AEAD_AES_128_GCM [RFC5116]
  IV length:   12 bytes
  KDF:         HMAC-SHA-256

Cipher Suite 6 (LISP_256_EC25519_CHACHA20_POLY1305):

  Diffie-Hellman Group: 256-bit Elliptic-Curve 25519 [CURVE25519]
  Encryption: Chacha20-Poly1305 [CHACHA-POLY] [RFC7539]
  Integrity:  Integrated with AEAD_CHACHA20_POLY1305 [CHACHA-POLY]
  IV length:  8 bytes
  KDF:        HMAC-SHA-256

Farinacci & Weis Experimental [Page 7] RFC 8061 LISP Data-Plane Confidentiality February 2017

 The Public Key Material field contains the public key generated by
 one of the Cipher Suites defined above.  The length of the key, in
 octets, is encoded in the Key Length field.
 When an ITR, PITR, or RTR sends a Map-Request, they will encode their
 own RLOC in the Security Key LCAF Type format within the ITR-RLOCs
 field.  When an ETR or RTR sends a Map-Reply, they will encode their
 RLOCs in Security Key LCAF Type format within the RLOC-record field
 of each EID-record supplied.
 If an ITR, PITR, or RTR sends a Map-Request with the Security Key
 LCAF Type included and the ETR or RTR does not want to have
 encapsulated traffic encrypted, they will return a Map-Reply with no
 RLOC-records encoded with the Security Key LCAF Type.  This signals
 to the ITR, PITR, or RTR not to encrypt traffic (it cannot encrypt
 traffic anyway since no ETR public key was returned).
 Likewise, if an ITR or PITR wishes to include multiple key-ids in the
 Map-Request, but the ETR or RTR wishes to use some but not all of the
 key-ids, it returns a Map-Reply only for those key-ids it wishes to
 use.

7. Shared Keys Used for the Data Plane

 When an ITR or PITR receives a Map-Reply accepting the Cipher Suite
 sent in the Map-Request, it is ready to create data-plane keys.  The
 same process is followed by the ETR or RTR returning the Map-Reply.
 The first step is to create a shared secret, using the peer's shared
 Diffie-Hellman Public Key Material combined with the device's own
 private keying material, as described in Section 5.  The Diffie-
 Hellman parameters used are defined in the Cipher Suite sent in the
 Map-Request and copied into the Map-Reply.
 The resulting shared secret is used to compute an AEAD-key for the
 algorithms specified in the Cipher Suite.  A Key Derivation Function
 (KDF) in counter mode, as specified by [NIST-SP800-108], is used to
 generate the data-plane keys.  The amount of keying material that is
 derived depends on the algorithms in the Cipher Suite.
 The inputs to the KDF are as follows:
 o  KDF function.  This is HMAC-SHA-256 in this document, but
    generally specified in each Cipher Suite definition.
 o  A key for the KDF function.  This is the computed Diffie-Hellman
    shared secret.

Farinacci & Weis Experimental [Page 8] RFC 8061 LISP Data-Plane Confidentiality February 2017

 o  Context that binds the use of the data-plane keys to this session.
    The context is made up of the following fields, which are
    concatenated and provided as the data to be acted upon by the KDF
    function.  A Context is made up of the following components:
  • A counter, represented as a two-octet value in network byte

order.

  • The null-terminated string "lisp-crypto".
  • The ITR's nonce from the Map-Request the Cipher Suite was

included in.

  • The number of bits of keying material required (L), represented

as a two-octet value in network byte order.

 The counter value in the context is first set to 1.  When the amount
 of keying material exceeds the number of bits returned by the KDF
 function, then the KDF function is called again with the same inputs
 except that the counter increments for each call.  When enough keying
 material is returned, it is concatenated and used to create keys.
 For example, AES with 128-bit keys requires 16 octets (128 bits) of
 keying material, and HMAC-SHA1-96 requires another 16 octets (128
 bits) of keying material in order to maintain a consistent 128 bits
 of security.  Since 32 octets (256 bits) of keying material are
 required, and the KDF function HMAC-SHA-256 outputs 256 bits, only
 one call is required.  The inputs are as follows:
 key-material = HMAC-SHA-256(dh-shared-secret, context)
     where: context = 0x0001 || "lisp-crypto" || <itr-nonce> || 0x0100
 In contrast, a Cipher Suite specifying AES with 256-bit keys requires
 32 octets (256 bits) of keying material, and HMAC-SHA256-128 requires
 another 32 octets (256 bits) of keying material in order to maintain
 a consistent 256 bits of security.  Since 64 octets (512 bits) of
 keying material are required, and the KDF function HMAC-SHA-256
 outputs 256 bits, two calls are required.

Farinacci & Weis Experimental [Page 9] RFC 8061 LISP Data-Plane Confidentiality February 2017

 key-material-1 = HMAC-SHA-256(dh-shared-secret, context)
     where: context = 0x0001 || "lisp-crypto" || <itr-nonce> || 0x0200
 key-material-2 = HMAC-SHA-256(dh-shared-secret, context)
     where: context = 0x0002 || "lisp-crypto" || <itr-nonce> || 0x0200
 key-material = key-material-1 || key-material-2
 If the key-material is longer than the required number of bits (L),
 then only the most significant L bits are used.
 From the derived key-material, the most significant 256 bits are used
 for the AEAD-key by AEAD ciphers.  The 256-bit AEAD-key is divided
 into a 128-bit encryption key and a 128-bit integrity check key
 internal to the cipher used by the ITR.

8. Data-Plane Operation

 The LISP encapsulation header [RFC6830] requires changes to encode
 the key-id for the key being used for encryption.
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ |       Source Port = xxxx      |       Dest Port = 4341        |

UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

\ |           UDP Length          |        UDP Checksum           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

L / |N|L|E|V|I|R|K|K| Nonce/Map-Version |\ \ I +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |A S \ | Instance ID/Locator-Status-Bits | |D P +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |/

  |                   Initialization Vector (IV)                  | I

E +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ C n / | | V c | | | r | Packet Payload with EID Header … | | y | | | p \ | |/ t +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   K-bits Indicate When a Packet Is Encrypted and Which Key Is Used

Farinacci & Weis Experimental [Page 10] RFC 8061 LISP Data-Plane Confidentiality February 2017

 When the KK bits are 00, the encapsulated packet is not encrypted.
 When the value of the KK bits is 1, 2, or 3, it encodes the key-id of
 the secret keys computed during the Diffie-Hellman
 Map-Request/Map-Reply exchange.  When the KK bits are not 0, the
 payload is prepended with an Initialization Vector (IV).  The length
 of the IV field is based on the Cipher Suite used.  Since all Cipher
 Suites defined in this document do Authenticated Encryption with
 Associated Data (AEAD), an ICV field does not need to be present in
 the packet since it is included in the ciphertext.  The Additional
 Data (AD) used for the ICV is shown above and includes the LISP
 header, the IV field, and the packet payload.
 When an ITR or PITR receives a packet to be encapsulated, the device
 will first decide what key to use, encode the key-id into the LISP
 header, and use that key to encrypt all packet data that follows the
 LISP header.  Therefore, the outer header, UDP header, and LISP
 header travel as plaintext.
 At the time of writing, there is an open working group item to
 discuss if the data encapsulation header needs change for encryption
 or any new applications.  This document proposes changes to the
 existing header so experimentation can continue without making large
 changes to the data plane at this time.  This document allocates two
 bits of the previously unused three flag bits (note the R-bit above
 is still a reserved flag bit, as documented in [RFC6830]) for the KK
 bits.

9. Procedures for Encryption and Decryption

 When an ITR, PITR, or RTR encapsulates a packet and has already
 computed an AEAD-key (detailed in Section 7) that is associated with
 a destination RLOC, the following encryption and encapsulation
 procedures are performed:
 1.  The encapsulator creates an IV and prepends the IV value to the
     packet being encapsulated.  For GCM and ChaCha20 Cipher Suites,
     the IV is incremented for every packet (beginning with a value of
     1 in the first packet) and sent to the destination RLOC.  For CBC
     Cipher Suites, the IV is a new random number for every packet
     sent to the destination RLOC.  For the ChaCha20 Cipher Suite, the
     IV is an 8-byte random value that is appended to a 4-byte counter
     that is incremented for every packet (beginning with a value of 1
     in the first packet).
 2.  Next encrypt with cipher function AES or ChaCha20 using the AEAD-
     key over the packet payload following the AEAD specification
     referenced in the Cipher Suite definition.  This does not include
     the IV.  The IV must be transmitted as plaintext so the decrypter

Farinacci & Weis Experimental [Page 11] RFC 8061 LISP Data-Plane Confidentiality February 2017

     can use it as input to the decryption cipher.  The payload should
     be padded to an integral number of bytes a block cipher may
     require.  The result of the AEAD operation may contain an ICV,
     the size of which is defined by the referenced AEAD
     specification.  Note that the AD (i.e., the LISP header exactly
     as will be prepended in the next step and the IV) must be given
     to the AEAD encryption function as the "associated data"
     argument.
 3.  Prepend the LISP header.  The key-id field of the LISP header is
     set to the key-id value that corresponds to key-pair used for the
     encryption cipher.
 4.  Lastly, prepend the UDP header and outer IP header onto the
     encrypted packet and send packet to destination RLOC.
 When an ETR, PETR, or RTR receives an encapsulated packet, the
 following decapsulation and decryption procedures are performed:
 1.  The outer IP header, UDP header, LISP header, and IV field are
     stripped from the start of the packet.  The LISP header and IV
     are retained and given to the AEAD decryption operation as the
     "associated data" argument.
 2.  The packet is decrypted using the AEAD-key and the IV from the
     packet.  The AEAD-key is obtained from a local-cache associated
     with the key-id value from the LISP header.  The result of the
     decryption function is a plaintext packet payload if the cipher
     returned a verified ICV.  Otherwise, the packet is invalid and is
     discarded.  If the AEAD specification included an ICV, the AEAD
     decryption function will locate the ICV in the ciphertext and
     compare it to a version of the ICV that the AEAD decryption
     function computes.  If the computed ICV is different than the ICV
     located in the ciphertext, then it will be considered tampered.
 3.  If the packet was not tampered with, the decrypted packet is
     forwarded to the destination EID.

10. Dynamic Rekeying

 Since multiple keys can be encoded in both control and data messages,
 an ITR can encapsulate and encrypt with a specific key while it is
 negotiating other keys with the same ETR.  As soon as an ETR or RTR
 returns a Map-Reply, it should be prepared to decapsulate and decrypt
 using the new keys computed with the new Diffie-Hellman parameters
 received in the Map-Request and returned in the Map-Reply.

Farinacci & Weis Experimental [Page 12] RFC 8061 LISP Data-Plane Confidentiality February 2017

 RLOC-probing can be used to change keys or Cipher Suites by the ITR
 at any time.  And when an initial Map-Request is sent to populate the
 ITR's map-cache, the Map-Request flows across the mapping system
 where a single ETR from the Map-Reply RLOC-set will respond.  If the
 ITR decides to use the other RLOCs in the RLOC-set, it MUST send a
 Map-Request directly to negotiate security parameters with the ETR.
 This process may be used to test reachability from an ITR to an ETR
 initially when a map-cache entry is added for the first time, so an
 ITR can get both reachability status and keys negotiated with one
 Map-Request/Map-Reply exchange.
 A rekeying event is defined to be when an ITR or PITR changes the
 Cipher Suite or public key in the Map-Request.  The ETR or RTR
 compares the Cipher Suite and public key it last received from the
 ITR for the key-id, and if any value has changed, it computes a new
 public key and Cipher Suite requested by the ITR from the Map-Request
 and returns it in the Map-Reply.  Now a new shared secret is computed
 and can be used for the key-id for encryption by the ITR and
 decryption by the ETR.  When the ITR or PITR starts this process of
 negotiating a new key, it must not use the corresponding key-id in
 encapsulated packets until it receives a Map-Reply from the ETR with
 the same Cipher Suite value it expects (the values it sent in a Map-
 Request).
 Note when RLOC-probing continues to maintain RLOC reachability and
 rekeying is not desirable, the ITR or RTR can either not include the
 Security Key LCAF Type in the Map-Request or supply the same key
 material as it received from the last Map-Reply from the ETR or RTR.
 This approach signals to the ETR or RTR that no rekeying event is
 requested.

11. Future Work

 For performance considerations, newer Elliptic-Curve Diffie-Hellman
 (ECDH) groups can be used as specified in [RFC4492] and [RFC6090] to
 reduce CPU cycles required to compute shared secret keys.
 For better security considerations as well as to be able to build
 faster software implementations, newer approaches to ciphers and
 authentication methods will be researched and tested.  Some examples
 are ChaCha20 and Poly1305 [CHACHA-POLY] [RFC7539].

Farinacci & Weis Experimental [Page 13] RFC 8061 LISP Data-Plane Confidentiality February 2017

12. Security Considerations

12.1. SAAG Support

 The LISP working group received security advice and guidance from the
 Security Area Advisory Group (SAAG).  The SAAG has been involved
 early in the design process, and their input and reviews have been
 included in this document.
 Comments from the SAAG included:
 1.  Do not use asymmetric ciphers in the data plane.
 2.  Consider adding ECDH early in the design.
 3.  Add Cipher Suites because ciphers are created more frequently
     than protocols that use them.
 4.  Consider the newer AEAD technology so authentication comes with
     doing encryption.

12.2. LISP-Crypto Security Threats

 Since ITRs and ETRs participate in key exchange over a public
 non-secure network, a man in the middle (MITM) could circumvent the
 key exchange and compromise data-plane confidentiality.  This can
 happen when the MITM is acting as a Map-Replier and provides its own
 public key so the ITR and the MITM generate a shared secret key
 between them.  If the MITM is in the data path between the ITR and
 ETR, it can use the shared secret key to decrypt traffic from the
 ITR.
 Since LISP can secure Map-Replies by the authentication process
 specified in [LISP-SEC], the ITR can detect when a MITM has signed a
 Map-Reply for an EID-prefix for which it is not authoritative.  When
 an ITR determines that the signature verification fails, it discards
 and does not reuse the key exchange parameters, avoids using the ETR
 for encapsulation, and issues a severe log message to the network
 administrator.  Optionally, the ITR can send RLOC-probes to the
 compromised RLOC to determine if the authoritative ETR is reachable.
 And when the ITR validates the signature of a Map-Reply, it can begin
 encrypting and encapsulating packets to the RLOC of ETR.

Farinacci & Weis Experimental [Page 14] RFC 8061 LISP Data-Plane Confidentiality February 2017

13. IANA Considerations

 This document describes a mechanism for encrypting LISP-encapsulated
 packets based on Diffie-Hellman key exchange procedures.  During the
 exchange, the devices have to agree on a Cipher Suite to be used
 (i.e., the cipher and hash functions used to encrypt/decrypt and to
 sign/verify packets).  The 8-bit Cipher Suite field is reserved for
 such purpose in the security material section of the Map-Request and
 Map-Reply messages.
 IANA has created a new registry (as outlined in [RFC5226]) titled
 "LISP Crypto Cipher Suite".  Initial values for the registry are
 provided below.  Future assignments are to be made on a "First Come,
 First Served" basis [RFC5226].
 +-----+--------------------------------------------+------------+
 |Value| Suite                                      | Reference  |
 +-----+--------------------------------------------+------------+
 |  0  | Reserved                                   | Section 6  |
 +-----+--------------------------------------------+------------+
 |  1  | LISP_2048MODP_AES128_CBC_SHA256            | Section 6  |
 +-----+--------------------------------------------+------------+
 |  2  | LISP_EC25519_AES128_CBC_SHA256             | Section 6  |
 +-----+--------------------------------------------+------------+
 |  3  | LISP_2048MODP_AES128_GCM                   | Section 6  |
 +-----+--------------------------------------------+------------+
 |  4  | LISP_3072MODP_AES128_GCM                   | Section 6  |
 +-----+--------------------------------------------+------------+
 |  5  | LISP_256_EC25519_AES128_GCM                | Section 6  |
 +-----+--------------------------------------------+------------+
 |  6  | LISP_256_EC25519_CHACHA20_POLY1305         | Section 6  |
 +-----+--------------------------------------------+------------+
                       LISP Crypto Cipher Suites

Farinacci & Weis Experimental [Page 15] RFC 8061 LISP Data-Plane Confidentiality February 2017

14. References

14.1. Normative References

 [NIST-SP800-108]
            National Institute of Standards and Technology,
            "Recommendation for Key Derivation Using Pseudorandom
            Functions", NIST Special Publication SP 800-108,
            DOI 10.6028/NIST.SP.800-108, October 2009.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2631]  Rescorla, E., "Diffie-Hellman Key Agreement Method",
            RFC 2631, DOI 10.17487/RFC2631, June 1999,
            <http://www.rfc-editor.org/info/rfc2631>.
 [RFC3526]  Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
            Diffie-Hellman groups for Internet Key Exchange (IKE)",
            RFC 3526, DOI 10.17487/RFC3526, May 2003,
            <http://www.rfc-editor.org/info/rfc3526>.
 [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
            Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
            for Transport Layer Security (TLS)", RFC 4492,
            DOI 10.17487/RFC4492, May 2006,
            <http://www.rfc-editor.org/info/rfc4492>.
 [RFC5116]  McGrew, D., "An Interface and Algorithms for Authenticated
            Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
            <http://www.rfc-editor.org/info/rfc5116>.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            DOI 10.17487/RFC5226, May 2008,
            <http://www.rfc-editor.org/info/rfc5226>.
 [RFC6090]  McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
            Curve Cryptography Algorithms", RFC 6090,
            DOI 10.17487/RFC6090, February 2011,
            <http://www.rfc-editor.org/info/rfc6090>.
 [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
            Locator/ID Separation Protocol (LISP)", RFC 6830,
            DOI 10.17487/RFC6830, January 2013,
            <http://www.rfc-editor.org/info/rfc6830>.

Farinacci & Weis Experimental [Page 16] RFC 8061 LISP Data-Plane Confidentiality February 2017

 [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
            Morris, J., Hansen, M., and R. Smith, "Privacy
            Considerations for Internet Protocols", RFC 6973,
            DOI 10.17487/RFC6973, July 2013,
            <http://www.rfc-editor.org/info/rfc6973>.
 [RFC7539]  Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
            Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015,
            <http://www.rfc-editor.org/info/rfc7539>.
 [RFC8060]  Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
            Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060,
            February 2017, <http://www.rfc-editor.org/info/rfc8060>.

14.2. Informative References

 [AES-CBC]  McGrew, D., Foley, J., and K. Paterson, "Authenticated
            Encryption with AES-CBC and HMAC-SHA", Work in Progress,
            draft-mcgrew-aead-aes-cbc-hmac-sha2-05, July 2014.
 [CHACHA-POLY]
            Langley, A. and W. Chang, "ChaCha20 and Poly1305 based
            Cipher Suites for TLS", Work in Progress,
            draft-agl-tls-chacha20poly1305-04, November 2013.
 [CURVE25519]
            Bernstein, D., "Curve25519: new Diffie-Hellman speed
            records", DOI 10.1007/11745853_14,
            <http://www.iacr.org/cryptodb/archive/2006/
            PKC/3351/3351.pdf>.
 [DH]       Wikipedia, "Diffie-Hellman key exchange", January 2017,
            <https://en.wikipedia.org/w/index.php?title=Diffie%E2%80%9
            3Hellman_key_exchange&oldid=759611604>.
 [LISP-DDT] Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A.
            Smirnov, "LISP Delegated Database Tree", Work in
            Progress, draft-ietf-lisp-ddt-08, September 2016.
 [LISP-SEC] Maino, F., Ermagan, V., Cabellos, A., and D. Saucez,
            "LISP-Security (LISP-SEC)", Work in Progress,
            draft-ietf-lisp-sec-12, November 2016.

Farinacci & Weis Experimental [Page 17] RFC 8061 LISP Data-Plane Confidentiality February 2017

Acknowledgments

 The authors would like to thank Dan Harkins, Joel Halpern, Fabio
 Maino, Ed Lopez, Roger Jorgensen, and Watson Ladd for their interest,
 suggestions, and discussions about LISP data-plane security.  An
 individual thank you to LISP WG Chair Luigi Iannone for shepherding
 this document as well as contributing to the IANA Considerations
 section.
 The authors would like to give a special thank you to Ilari Liusvaara
 for his extensive commentary and discussion.  He has contributed his
 security expertise to make lisp-crypto as secure as the state of the
 art in cryptography.
 In addition, the support and suggestions from the SAAG working group
 were helpful and appreciated.

Authors' Addresses

 Dino Farinacci
 lispers.net
 San Jose, California  95120
 United States of America
 Phone: 408-718-2001
 Email: farinacci@gmail.com
 Brian Weis
 Cisco Systems
 170 West Tasman Drive
 San Jose, California  95124-1706
 United States of America
 Phone: 408-526-4796
 Email: bew@cisco.com

Farinacci & Weis Experimental [Page 18]

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