GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc2222

Network Working Group J. Myers Request for Comments: 2222 Netscape Communications Category: Standards Track October 1997

          Simple Authentication and Security Layer (SASL)

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1997).  All Rights Reserved.

Table of Contents

 1.    Abstract ..............................................    2
 2.    Organization of this Document .........................    2
 2.1.  How to Read This Document .............................    2
 2.2.  Conventions Used in this Document .....................    2
 2.3.  Examples ..............................................    3
 3.    Introduction and Overview .............................    3
 4.    Profiling requirements ................................    4
 5.    Specific issues .......................................    5
 5.1.  Client sends data first ...............................    5
 5.2.  Server returns success with additional data ...........    5
 5.3.  Multiple authentications ..............................    5
 6.    Registration procedures ...............................    6
 6.1.  Comments on SASL mechanism registrations ..............    6
 6.2.  Location of Registered SASL Mechanism List ............    6
 6.3.  Change Control ........................................    7
 6.4.  Registration Template .................................    7
 7.    Mechanism definitions .................................    8
 7.1.  Kerberos version 4 mechanism ..........................    8
 7.2.  GSSAPI mechanism ......................................    9
 7.2.1 Client side of authentication protocol exchange .......    9
 7.2.2 Server side of authentication protocol exchange .......   10
 7.2.3 Security layer ........................................   11
 7.3.  S/Key mechanism .......................................   11
 7.4.  External mechanism ....................................   12
 8.    References ............................................   13
 9.    Security Considerations ...............................   13
 10.   Author's Address ......................................   14

Myers Standards Track [Page 1] RFC 2222 SASL October 1997

 Appendix A. Relation of SASL to Transport Security ..........   15
 Full Copyright Statement ....................................   16

1. Abstract

 This document describes a method for adding authentication support to
 connection-based protocols.  To use this specification, a protocol
 includes a command for identifying and authenticating a user to a
 server and for optionally negotiating protection of subsequent
 protocol interactions.  If its use is negotiated, a security layer is
 inserted between the protocol and the connection.  This document
 describes how a protocol specifies such a command, defines several
 mechanisms for use by the command, and defines the protocol used for
 carrying a negotiated security layer over the connection.

2. Organization of this Document

2.1. How to Read This Document

 This document is written to serve two different audiences, protocol
 designers using this specification to support authentication in their
 protocol, and implementors of clients or servers for those protocols
 using this specification.
 The sections "Introduction and Overview", "Profiling requirements",
 and "Security Considerations" cover issues that protocol designers
 need to understand and address in profiling this specification for
 use in a specific protocol.
 Implementors of a protocol using this specification need the
 protocol-specific profiling information in addition to the
 information in this document.

2.2. Conventions Used in this Document

 In examples, "C:" and "S:" indicate lines sent by the client and
 server respectively.
 The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
 in this document are to be interpreted as defined in "Key words for
 use in RFCs to Indicate Requirement Levels" [RFC 2119].

Myers Standards Track [Page 2] RFC 2222 SASL October 1997

2.3. Examples

 Examples in this document are for the IMAP profile [RFC 2060] of this
 specification.  The base64 encoding of challenges and responses, as
 well as the "+ " preceding the responses are part of the IMAP4
 profile, not part of the SASL specification itself.

3. Introduction and Overview

 The Simple Authentication and Security Layer (SASL) is a method for
 adding authentication support to connection-based protocols.  To use
 this specification, a protocol includes a command for identifying and
 authenticating a user to a server and for optionally negotiating a
 security layer for subsequent protocol interactions.
 The command has a required argument identifying a SASL mechanism.
 SASL mechanisms are named by strings, from 1 to 20 characters in
 length, consisting of upper-case letters, digits, hyphens, and/or
 underscores.  SASL mechanism names must be registered with the IANA.
 Procedures for registering new SASL mechanisms are given in the
 section "Registration procedures"
 If a server supports the requested mechanism, it initiates an
 authentication protocol exchange.  This consists of a series of
 server challenges and client responses that are specific to the
 requested mechanism.  The challenges and responses are defined by the
 mechanisms as binary tokens of arbitrary length.  The protocol's
 profile then specifies how these binary tokens are then encoded for
 transfer over the connection.
 After receiving the authentication command or any client response, a
 server may issue a challenge, indicate failure, or indicate
 completion.  The protocol's profile specifies how the server
 indicates which of the above it is doing.
 After receiving a challenge, a client may issue a response or abort
 the exchange.  The protocol's profile specifies how the client
 indicates which of the above it is doing.
 During the authentication protocol exchange, the mechanism performs
 authentication, transmits an authorization identity (frequently known
 as a userid) from the client to server, and negotiates the use of a
 mechanism-specific security layer.  If the use of a security layer is
 agreed upon, then the mechanism must also define or negotiate the
 maximum cipher-text buffer size that each side is able to receive.

Myers Standards Track [Page 3] RFC 2222 SASL October 1997

 The transmitted authorization identity may be different than the
 identity in the client's authentication credentials.  This permits
 agents such as proxy servers to authenticate using their own
 credentials, yet request the access privileges of the identity for
 which they are proxying.  With any mechanism, transmitting an
 authorization identity of the empty string directs the server to
 derive an authorization identity from the client's authentication
 credentials.
 If use of a security layer is negotiated, it is applied to all
 subsequent data sent over the connection.  The security layer takes
 effect immediately following the last response of the authentication
 exchange for data sent by the client and the completion indication
 for data sent by the server.  Once the security layer is in effect,
 the protocol stream is processed by the security layer into buffers
 of cipher-text.  Each buffer is transferred over the connection as a
 stream of octets prepended with a four octet field in network byte
 order that represents the length of the following buffer.  The length
 of the cipher-text buffer must be no larger than the maximum size
 that was defined or negotiated by the other side.

4. Profiling requirements

 In order to use this specification, a protocol definition must supply
 the following information:
 1. A service name, to be selected from the IANA registry of "service"
    elements for the GSSAPI host-based service name form [RFC 2078].
 2. A definition of the command to initiate the authentication
    protocol exchange.  This command must have as a parameter the
    mechanism name being selected by the client.
    The command SHOULD have an optional parameter giving an initial
    response.  This optional parameter allows the client to avoid a
    round trip when using a mechanism which is defined to have the
    client send data first.  When this initial response is sent by the
    client and the selected mechanism is defined to have the server
    start with an initial challenge, the command fails.  See section
    5.1 of this document for further information.
 3. A definition of the method by which the authentication protocol
    exchange is carried out, including how the challenges and
    responses are encoded, how the server indicates completion or
    failure of the exchange, how the client aborts an exchange, and
    how the exchange method interacts with any line length limits in
    the protocol.

Myers Standards Track [Page 4] RFC 2222 SASL October 1997

 4. Identification of the octet where any negotiated security layer
    starts to take effect, in both directions.
 5. A specification of how the authorization identity passed from the
    client to the server is to be interpreted.

5. Specific issues

5.1. Client sends data first

 Some mechanisms specify that the first data sent in the
 authentication protocol exchange is from the client to the server.
 If a protocol's profile permits the command which initiates an
 authentication protocol exchange to contain an initial client
 response, this parameter SHOULD be used with such mechanisms.
 If the initial client response parameter is not given, or if a
 protocol's profile does not permit the command which initiates an
 authentication protocol exchange to contain an initial client
 response, then the server issues a challenge with no data.  The
 client's response to this challenge is then used as the initial
 client response.  (The server then proceeds to send the next
 challenge, indicates completion, or indicates failure.)

5.2. Server returns success with additional data

 Some mechanisms may specify that server challenge data be sent to the
 client along with an indication of successful completion of the
 exchange.  This data would, for example, authenticate the server to
 the client.
 If a protocol's profile does not permit this server challenge to be
 returned with a success indication, then the server issues the server
 challenge without an indication of successful completion.  The client
 then responds with no data.  After receiving this empty response, the
 server then indicates successful completion.

5.3. Multiple authentications

 Unless otherwise stated by the protocol's profile, only one
 successful SASL negotiation may occur in a protocol session.  In this
 case, once an authentication protocol exchange has successfully
 completed, further attempts to initiate an authentication protocol
 exchange fail.

Myers Standards Track [Page 5] RFC 2222 SASL October 1997

 In the case that a profile explicitly permits multiple successful
 SASL negotiations to occur, then in no case may multiple security
 layers be simultaneously in effect.  If a security layer is in effect
 and a subsequent SASL negotiation selects no security layer, the
 original security layer remains in effect.  If a security layer is in
 effect and a subsequent SASL negotiation selects a second security
 layer, then the second security layer replaces the first.

6. Registration procedures

 Registration of a SASL mechanism is done by filling in the template
 in section 6.4 and sending it in to iana@isi.edu.  IANA has the right
 to reject obviously bogus registrations, but will perform no review
 of clams made in the registration form.
 There is no naming convention for SASL mechanisms; any name that
 conforms to the syntax of a SASL mechanism name can be registered.
 While the registration procedures do not require it, authors of SASL
 mechanisms are encouraged to seek community review and comment
 whenever that is feasible.  Authors may seek community review by
 posting a specification of their proposed mechanism as an internet-
 draft.  SASL mechanisms intended for widespread use should be
 standardized through the normal IETF process, when appropriate.

6.1. Comments on SASL mechanism registrations

 Comments on registered SASL mechanisms should first be sent to the
 "owner" of the mechanism.  Submitters of comments may, after a
 reasonable attempt to contact the owner, request IANA to attach their
 comment to the SASL mechanism registration itself.  If IANA approves
 of this the comment will be made accessible in conjunction with the
 SASL mechanism registration itself.

6.2. Location of Registered SASL Mechanism List

 SASL mechanism registrations will be posted in the anonymous FTP
 directory "ftp://ftp.isi.edu/in-notes/iana/assignments/sasl-
 mechanisms/" and all registered SASL mechanisms will be listed in the
 periodically issued "Assigned Numbers" RFC [currently STD 2, RFC
 1700].  The SASL mechanism description and other supporting material
 may also be published as an Informational RFC by sending it to "rfc-
 editor@isi.edu" (please follow the instructions to RFC authors [RFC
 2223]).

Myers Standards Track [Page 6] RFC 2222 SASL October 1997

6.3. Change Control

 Once a SASL mechanism registration has been published by IANA, the
 author may request a change to its definition.  The change request
 follows the same procedure as the registration request.
 The owner of a SASL mechanism may pass responsibility for the SASL
 mechanism to another person or agency by informing IANA; this can be
 done without discussion or review.
 The IESG may reassign responsibility for a SASL mechanism. The most
 common case of this will be to enable changes to be made to
 mechanisms where the author of the registration has died, moved out
 of contact or is otherwise unable to make changes that are important
 to the community.
 SASL mechanism registrations may not be deleted; mechanisms which are
 no longer believed appropriate for use can be declared OBSOLETE by a
 change to their "intended use" field; such SASL mechanisms will be
 clearly marked in the lists published by IANA.
 The IESG is considered to be the owner of all SASL mechanisms which
 are on the IETF standards track.

6.4. Registration Template

 To: iana@iana.org
 Subject: Registration of SASL mechanism X
 SASL mechanism name:
 Security considerations:
 Published specification (optional, recommended):
 Person & email address to contact for further information:
 Intended usage:
 (One of COMMON, LIMITED USE or OBSOLETE)
 Author/Change controller:
 (Any other information that the author deems interesting may be
 added below this line.)

Myers Standards Track [Page 7] RFC 2222 SASL October 1997

7. Mechanism definitions

 The following mechanisms are hereby defined.

7.1. Kerberos version 4 mechanism

 The mechanism name associated with Kerberos version 4 is
 "KERBEROS_V4".
 The first challenge consists of a random 32-bit number in network
 byte order.  The client responds with a Kerberos ticket and an
 authenticator for the principal "service.hostname@realm", where
 "service" is the service name specified in the protocol's profile,
 "hostname" is the first component of the host name of the server with
 all letters in lower case, and where "realm" is the Kerberos realm of
 the server.  The encrypted checksum field included within the
 Kerberos authenticator contains the server provided challenge in
 network byte order.
 Upon decrypting and verifying the ticket and authenticator, the
 server verifies that the contained checksum field equals the original
 server provided random 32-bit number.  Should the verification be
 successful, the server must add one to the checksum and construct 8
 octets of data, with the first four octets containing the incremented
 checksum in network byte order, the fifth octet containing a bit-mask
 specifying the security layers supported by the server, and the sixth
 through eighth octets containing, in network byte order, the maximum
 cipher-text buffer size the server is able to receive.  The server
 must encrypt using DES ECB mode the 8 octets of data in the session
 key and issue that encrypted data in a second challenge.  The client
 considers the server authenticated if the first four octets of the
 un-encrypted data is equal to one plus the checksum it previously
 sent.
 The client must construct data with the first four octets containing
 the original server-issued checksum in network byte order, the fifth
 octet containing the bit-mask specifying the selected security layer,
 the sixth through eighth octets containing in network byte order the
 maximum cipher-text buffer size the client is able to receive, and
 the following octets containing the authorization identity.  The
 client must then append from one to eight zero-valued octets so that
 the length of the data is a multiple of eight octets. The client must
 then encrypt using DES PCBC mode the data with the session key and
 respond with the encrypted data.  The server decrypts the data and
 verifies the contained checksum.  The server must verify that the
 principal identified in the Kerberos ticket is authorized to connect
 as that authorization identity.  After this verification, the
 authentication process is complete.

Myers Standards Track [Page 8] RFC 2222 SASL October 1997

 The security layers and their corresponding bit-masks are as follows:
    1 No security layer
    2 Integrity (krb_mk_safe) protection
    4 Privacy (krb_mk_priv) protection
 Other bit-masks may be defined in the future; bits which are not
 understood must be negotiated off.
 EXAMPLE: The following are two Kerberos version 4 login scenarios to
 the IMAP4 protocol (note that the line breaks in the sample
 authenticators are for editorial clarity and are not in real
 authenticators)
   S: * OK IMAP4 Server
   C: A001 AUTHENTICATE KERBEROS_V4
   S: + AmFYig==
   C: BAcAQU5EUkVXLkNNVS5FRFUAOCAsho84kLN3/IJmrMG+25a4DT
      +nZImJjnTNHJUtxAA+o0KPKfHEcAFs9a3CL5Oebe/ydHJUwYFd
      WwuQ1MWiy6IesKvjL5rL9WjXUb9MwT9bpObYLGOKi1Qh
   S: + or//EoAADZI=
   C: DiAF5A4gA+oOIALuBkAAmw==
   S: A001 OK Kerberos V4 authentication successful
   S: * OK IMAP4 Server
   C: A001 AUTHENTICATE KERBEROS_V4
   S: + gcfgCA==
   C: BAcAQU5EUkVXLkNNVS5FRFUAOCAsho84kLN3/IJmrMG+25a4DT
      +nZImJjnTNHJUtxAA+o0KPKfHEcAFs9a3CL5Oebe/ydHJUwYFd
      WwuQ1MWiy6IesKvjL5rL9WjXUb9MwT9bpObYLGOKi1Qh
   S: A001 NO Kerberos V4 authentication failed

7.2. GSSAPI mechanism

 The mechanism name associated with all mechanisms employing the
 GSSAPI [RFC 2078] is "GSSAPI".

7.2.1 Client side of authentication protocol exchange

 The client calls GSS_Init_sec_context, passing in 0 for
 input_context_handle (initially) and a targ_name equal to output_name
 from GSS_Import_Name called with input_name_type of
 GSS_C_NT_HOSTBASED_SERVICE and input_name_string of
 "service@hostname" where "service" is the service name specified in
 the protocol's profile, and "hostname" is the fully qualified host
 name of the server.  The client then responds with the resulting
 output_token.  If GSS_Init_sec_context returns GSS_S_CONTINUE_NEEDED,

Myers Standards Track [Page 9] RFC 2222 SASL October 1997

 then the client should expect the server to issue a token in a
 subsequent challenge.  The client must pass the token to another call
 to GSS_Init_sec_context, repeating the actions in this paragraph.
 When GSS_Init_sec_context returns GSS_S_COMPLETE, the client takes
 the following actions: If the last call to GSS_Init_sec_context
 returned an output_token, then the client responds with the
 output_token, otherwise the client responds with no data.  The client
 should then expect the server to issue a token in a subsequent
 challenge.  The client passes this token to GSS_Unwrap and interprets
 the first octet of resulting cleartext as a bit-mask specifying the
 security layers supported by the server and the second through fourth
 octets as the maximum size output_message to send to the server.  The
 client then constructs data, with the first octet containing the
 bit-mask specifying the selected security layer, the second through
 fourth octets containing in network byte order the maximum size
 output_message the client is able to receive, and the remaining
 octets containing the authorization identity.  The client passes the
 data to GSS_Wrap with conf_flag set to FALSE, and responds with the
 generated output_message.  The client can then consider the server
 authenticated.

7.2.2 Server side of authentication protocol exchange

 The server passes the initial client response to
 GSS_Accept_sec_context as input_token, setting input_context_handle
 to 0 (initially).  If GSS_Accept_sec_context returns
 GSS_S_CONTINUE_NEEDED, the server returns the generated output_token
 to the client in challenge and passes the resulting response to
 another call to GSS_Accept_sec_context, repeating the actions in this
 paragraph.
 When GSS_Accept_sec_context returns GSS_S_COMPLETE, the client takes
 the following actions: If the last call to GSS_Accept_sec_context
 returned an output_token, the server returns it to the client in a
 challenge and expects a reply from the client with no data.  Whether
 or not an output_token was returned (and after receipt of any
 response from the client to such an output_token), the server then
 constructs 4 octets of data, with the first octet containing a bit-
 mask specifying the security layers supported by the server and the
 second through fourth octets containing in network byte order the
 maximum size output_token the server is able to receive.  The server
 must then pass the plaintext to GSS_Wrap with conf_flag set to FALSE
 and issue the generated output_message to the client in a challenge.
 The server must then pass the resulting response to GSS_Unwrap and
 interpret the first octet of resulting cleartext as the bit-mask for
 the selected security layer, the second through fourth octets as the
 maximum size output_message to send to the client, and the remaining

Myers Standards Track [Page 10] RFC 2222 SASL October 1997

 octets as the authorization identity.  The server must verify that
 the src_name is authorized to authenticate as the authorization
 identity.  After these verifications, the authentication process is
 complete.

7.2.3 Security layer

 The security layers and their corresponding bit-masks are as follows:
   1 No security layer
   2 Integrity protection.
     Sender calls GSS_Wrap with conf_flag set to FALSE
   4 Privacy protection.
     Sender calls GSS_Wrap with conf_flag set to TRUE
 Other bit-masks may be defined in the future; bits which are not
 understood must be negotiated off.

7.3. S/Key mechanism

 The mechanism name associated with S/Key [RFC 1760] using the MD4
 digest algorithm is "SKEY".
 The client sends an initial response with the authorization identity.
 The server then issues a challenge which contains the decimal
 sequence number followed by a single space and the seed string for
 the indicated authorization identity.  The client responds with the
 one-time-password, as either a 64-bit value in network byte order or
 encoded in the "six English words" format.
 The server must verify the one-time-password.  After this
 verification, the authentication process is complete.
 S/Key authentication does not provide for any security layers.
 EXAMPLE: The following are two S/Key login scenarios in the IMAP4
 protocol.
   S: * OK IMAP4 Server
   C: A001 AUTHENTICATE SKEY
   S: +
   C: bW9yZ2Fu
   S: + OTUgUWE1ODMwOA==
   C: Rk9VUiBNQU5OIFNPT04gRklSIFZBUlkgTUFTSA==
   S: A001 OK S/Key authentication successful

Myers Standards Track [Page 11] RFC 2222 SASL October 1997

   S: * OK IMAP4 Server
   C: A001 AUTHENTICATE SKEY
   S: +
   C: c21pdGg=
   S: + OTUgUWE1ODMwOA==
   C: BsAY3g4gBNo=
   S: A001 NO S/Key authentication failed
 The following is an S/Key login scenario in an IMAP4-like protocol
 which has an optional "initial response" argument to the AUTHENTICATE
 command.
   S: * OK IMAP4-Like Server
   C: A001 AUTHENTICATE SKEY bW9yZ2Fu
   S: + OTUgUWE1ODMwOA==
   C: Rk9VUiBNQU5OIFNPT04gRklSIFZBUlkgTUFTSA==
   S: A001 OK S/Key authentication successful

7.4. External mechanism

 The mechanism name associated with external authentication is
 "EXTERNAL".
 The client sends an initial response with the authorization identity.
 The server uses information, external to SASL, to determine whether
 the client is authorized to authenticate as the authorization
 identity.  If the client is so authorized, the server indicates
 successful completion of the authentication exchange; otherwise the
 server indicates failure.
 The system providing this external information may be, for example,
 IPsec or TLS.
 If the client sends the empty string as the authorization identity
 (thus requesting the authorization identity be derived from the
 client's authentication credentials), the authorization identity is
 to be derived from authentication credentials which exist in the
 system which is providing the external authentication.

Myers Standards Track [Page 12] RFC 2222 SASL October 1997

8. References

 [RFC 2060] Crispin, M., "Internet Message Access Protocol - Version
            4rev1", RFC 2060, December 1996.
 [RFC 2078] Linn, J., "Generic Security Service Application Program
            Interface, Version 2", RFC 2078, January 1997.
 [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", RFC 2119, March 1997.
 [RFC 2223] Postel, J., and J. Reynolds, "Instructions to RFC
            Authors", RFC 2223, October 1997.
 [RFC 1760] Haller, N., "The S/Key One-Time Password System", RFC
            1760, February 1995.
 [RFC 1700] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2,
            RFC 1700, October 1994.

9. Security Considerations

 Security issues are discussed throughout this memo.
 The mechanisms that support integrity protection are designed such
 that the negotiation of the security layer and authorization identity
 is integrity protected.  When the client selects a security layer
 with at least integrity protection, this protects against an active
 attacker hijacking the connection and modifying the authentication
 exchange to negotiate a plaintext connection.
 When a server or client supports multiple authentication mechanisms,
 each of which has a different security strength, it is possible for
 an active attacker to cause a party to use the least secure mechanism
 supported.  To protect against this sort of attack, a client or
 server which supports mechanisms of different strengths should have a
 configurable minimum strength that it will use.  It is not sufficient
 for this minimum strength check to only be on the server, since an
 active attacker can change which mechanisms the client sees as being
 supported, causing the client to send authentication credentials for
 its weakest supported mechanism.

Myers Standards Track [Page 13] RFC 2222 SASL October 1997

 The client's selection of a SASL mechanism is done in the clear and
 may be modified by an active attacker.  It is important for any new
 SASL mechanisms to be designed such that an active attacker cannot
 obtain an authentication with weaker security properties by modifying
 the SASL mechanism name and/or the challenges and responses.
 Any protocol interactions prior to authentication are performed in
 the clear and may be modified by an active attacker.  In the case
 where a client selects integrity protection, it is important that any
 security-sensitive protocol negotiations be performed after
 authentication is complete.  Protocols should be designed such that
 negotiations performed prior to authentication should be either
 ignored or revalidated once authentication is complete.

10. Author's Address

 John G. Myers
 Netscape Communications
 501 E. Middlefield Road
 Mail Stop MV-029
 Mountain View, CA 94043-4042
 EMail: jgmyers@netscape.com

Myers Standards Track [Page 14] RFC 2222 SASL October 1997

Appendix A. Relation of SASL to Transport Security

 Questions have been raised about the relationship between SASL and
 various services (such as IPsec and TLS) which provide a secured
 connection.
 Two of the key features of SASL are:
 1. The separation of the authorization identity from the identity in
    the client's credentials.  This permits agents such as proxy
    servers to authenticate using their own credentials, yet request
    the access privileges of the identity for which they are proxying.
 2. Upon successful completion of an authentication exchange, the
    server knows the authorization identity the client wishes to use.
    This allows servers to move to a "user is authenticated" state in
    the protocol.
 These features are extremely important to some application protocols,
 yet Transport Security services do not always provide them.  To
 define SASL mechanisms based on these services would be a very messy
 task, as the framing of these services would be redundant with the
 framing of SASL and some method of providing these important SASL
 features would have to be devised.
 Sometimes it is desired to enable within an existing connection the
 use of a security service which does not fit the SASL model.  (TLS is
 an example of such a service.)  This can be done by adding a command,
 for example "STARTTLS", to the protocol.  Such a command is outside
 the scope of SASL, and should be different from the command which
 starts a SASL authentication protocol exchange.
 In certain situations, it is reasonable to use SASL underneath one of
 these Transport Security services.  The transport service would
 secure the connection, either service would authenticate the client,
 and SASL would negotiate the authorization identity.  The SASL
 negotiation would be what moves the protocol from "unauthenticated"
 to "authenticated" state.  The "EXTERNAL" SASL mechanism is
 explicitly intended to handle the case where the transport service
 secures the connection and authenticates the client and SASL
 negotiates the authorization identity.
 When using SASL underneath a sufficiently strong Transport Security
 service, a SASL security layer would most likely be redundant.  The
 client and server would thus probably want to negotiate off the use
 of a SASL security layer.

Myers Standards Track [Page 15] RFC 2222 SASL October 1997

Full Copyright Statement

 Copyright (C) The Internet Society (1997).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implmentation may be prepared, copied, published
 andand distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Myers Standards Track [Page 16]

/data/webs/external/dokuwiki/data/pages/rfc/rfc2222.txt · Last modified: 1997/10/28 22:25 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki