draft-ietf-sasl-rfc2222bis-00.txt   draft-ietf-sasl-rfc2222bis-01.txt 
Network Working Group A. Melnikov Network Working Group A. Melnikov
Internet Draft Editor
Document: draft-ietf-sasl-rfc2222bis-00.txt Document: draft-ietf-sasl-rfc2222bis-01.txt June 2003
Expires in six months Expires in six months
Simple Authentication and Security Layer (SASL) Simple Authentication and Security Layer (SASL)
Status of this Memo Status of this Memo
This document is an Internet Draft and is in full conformance with This document is an Internet Draft and is in full conformance with
all provisions of Section 10 of RFC 2026. all provisions of Section 10 of RFC 2026.
Internet Drafts are working documents of the Internet Engineering Internet Drafts are working documents of the Internet Engineering
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http://www.ietf.org/ietf/1id-abstracts.txt http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
A revised version of this draft document will be submitted to the RFC A revised version of this draft document will be submitted to the RFC
editor as a Draft Standard for the Internet Community. Discussion editor as a Draft Standard for the Internet Community. Discussion
and suggestions for improvement are requested. Distribution of this and suggestions for improvement are requested. Distribution of this
draft is unlimited. draft is unlimited.
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1. Abstract 1. Abstract
SASL provides a method for adding authentication support with an SASL provides a method for adding authentication support with an
optional security layer to connection-based protocols. It also optional security layer to connection-based protocols. It also
describes a structure for authentication mechanisms. The result is describes a structure for authentication mechanisms. The result is
an abstraction layer between protocols and authentication mechanisms an abstraction layer between protocols and authentication mechanisms
such that any SASL-compatible authentication mechanism can be used such that any SASL-compatible authentication mechanism can be used
with any SASL-compatible protocol. with any SASL-compatible protocol.
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in this document are to be interpreted as defined in "Key words for in this document are to be interpreted as defined in "Key words for
use in RFCs to Indicate Requirement Levels" [KEYWORDS]. use in RFCs to Indicate Requirement Levels" [KEYWORDS].
3. Overview 3. Overview
The Simple Authentication and Security Layer (SASL) is a method for The Simple Authentication and Security Layer (SASL) is a method for
adding authentication support to connection-based protocols. adding authentication support to connection-based protocols.
The SASL specification has three layers, as indicated in the diagram The SASL specification has three layers, as indicated in the diagram
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below. At the top, a protocol definition using SASL specifies a below. At the top, a protocol definition using SASL specifies a
profile, including a command for identifying and authenticating a profile, including a command for identifying and authenticating a
user to a server and for optionally negotiating a security layer for user to a server and for optionally negotiating a security layer for
subsequent protocol interactions. At the bottom, a SASL mechanism subsequent protocol interactions. At the bottom, a SASL mechanism
definition specifies an authentication mechanism. The SASL definition specifies an authentication mechanism. The SASL
framework, specified by this document, constrains the behavior of framework, specified by this document, constrains the behavior of
protocol profiles and mechanisms, separating protocol from mechanism protocol profiles and mechanisms, separating protocol from mechanism
and defining how they interact. and defining how they interact.
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The "sasl-mech" rule below defines the syntax of a SASL mechanism The "sasl-mech" rule below defines the syntax of a SASL mechanism
name. This uses the augmented Backus-Naur Form (BNF) notation as name. This uses the augmented Backus-Naur Form (BNF) notation as
specified in [ABNF] and the ABNF core rules as specified in Appendix specified in [ABNF] and the ABNF core rules as specified in Appendix
A of the ABNF specification [ABNF]. A of the ABNF specification [ABNF].
sasl-mech = 1*20mech-char sasl-mech = 1*20mech-char
mech-char = %x41-5A / DIGIT / "-" / "_" mech-char = %x41-5A / DIGIT / "-" / "_"
; mech names restricted to uppercase letters, ; mech names restricted to uppercase letters,
; digits, "-" and "_" ; digits, "-" and "_"
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4.1. Authentication protocol exchange 4.1. Authentication protocol exchange
A SASL mechanism is responsible for conducting an authentication A SASL mechanism is responsible for conducting an authentication
protocol exchange. This consists of a series of server challenges protocol exchange. This consists of a series of server challenges
and client responses, the contents of which are specific to and and client responses, the contents of which are specific to and
defined by the mechanism. To the protocol, the challenges and defined by the mechanism. To the protocol, the challenges and
responses are opaque binary tokens of arbitrary length. The responses are opaque binary tokens of arbitrary length. The
protocol's profile then specifies how these binary tokens are then protocol's profile then specifies how these binary tokens are then
encoded for transfer over the connection. encoded for transfer over the connection.
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server as the primary identity for making access policy decisions. server as the primary identity for making access policy decisions.
The character encoding scheme used for transmitting an authorization The character encoding scheme used for transmitting an authorization
identity over protocol is specified in each authentication mechanism identity over protocol is specified in each authentication mechanism
(with the authentication mechanism's blob being further (with the authentication mechanism's blob being further
restricted/encoded by the protocol profile). Per IETF character set restricted/encoded by the protocol profile). Per IETF character set
policy [CHARSET-POLICY], authentication mechanisms SHOULD encode policy [CHARSET-POLICY], authentication mechanisms SHOULD encode
these and other strings in UTF-8 [UTF-8]. While some legacy these and other strings in UTF-8 [UTF-8]. While some legacy
mechanisms are incapable of transmitting an authoriation identity mechanisms are incapable of transmitting an authoriation identity
other than the empty string, newly defined mechanisms are expected to other than the empty string, newly defined mechanisms are expected to
be capable of carrying the entire repertoire of Unicode Normalization be capable of carrying the entire Unicode repertoire (with the
form KC [UNICODE-NORMALIZATION] (with the exception of the NUL exception of the NUL character). An authorization identity of the
character). empty string and and an absent authorization identity MUST be treated
as equivalent. However, mechanisms SHOULD NOT allow both (i.e. if
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authorization identity is transferred, it SHOULD NOT be an empty
string).
The identity derived from the client's authentication credentials is The identity derived from the client's authentication credentials is
known as the "authentication identity". With any mechanism, known as the "authentication identity". With any mechanism,
transmitting an authorization identity of the empty string directs transmitting an authorization identity of the empty string directs
the server to derive an authorization identity from the client's the server to derive an authorization identity from the client's
authentication identity. authentication identity.
If the authorization identity transmitted during the authentication If the authorization identity transmitted during the authentication
protocol exchange is not the empty string, this is typically referred protocol exchange is not the empty string, this is typically referred
to as "proxy authentication". This feature permits agents such as to as "proxy authentication". This feature permits agents such as
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privileges of the authorization identity and whether the privileges of the authorization identity and whether the
authorization identity is permitted to receive service. If it is authorization identity is permitted to receive service. If it is
not, the server indicates failure of the authentication protocol not, the server indicates failure of the authentication protocol
exchange. exchange.
As a client might not have the same information as the server, As a client might not have the same information as the server,
clients SHOULD NOT themselves try to derive authorization identities clients SHOULD NOT themselves try to derive authorization identities
from authentication identities when clients could instead transmit an from authentication identities when clients could instead transmit an
authorization identity of the empty string. authorization identity of the empty string.
<<Is transmitting an empty authorization id is the same as not
transmitting it at all? Why would we encourage two ways to do the
same thing?>>
The server SHOULD verify the correctness of a received authorization The server SHOULD verify the correctness of a received authorization
identity. For example, an IMAP [RFC 3501] server will prepare the identity. Profiles whose authorization identities are simple user
received authorization identity using the "SASLPrep" profile names (e.g. IMAP [RFC 3501]) are encouraged to employ [SASLPrep]
[SASLPrep] of the "stringprep" algorithm [StringPrep]. If the profile [SASLPrep] of the "stringprep" algorithm [StringPrep] to
preparation of the authorization identity fails or results in an prepare these names for matching. If the preparation of the
empty string, the server MUST fail the authentication exchange. The authorization identity fails or results in an empty string, the
only exception to this rule is when the received authorization server MUST fail the authentication exchange. The only exception to
identity is the empty string. this rule is when the received authorization identity is already the
empty string.
4.3. Security layers 4.3. Security layers
If use of a security layer is negotiated by the authentication If use of a security layer is negotiated by the authentication
protocol exchange, the security layer is applied to all subsequent protocol exchange, the security layer is applied to all subsequent
data sent over the connection. The security layer takes effect data sent over the connection. The security layer takes effect
immediately following the last response of the authentication immediately following the last response of the authentication
exchange for data sent by the client and the completion indication exchange for data sent by the client and the completion indication
for data sent by the server. for data sent by the server.
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Once the security layer is in effect, the protocol stream is
processed by the security layer into buffers of security encoded processed by the security layer into buffers of security encoded
data. Each buffer of security encoded data is transferred over the data. Each buffer of security encoded data is transferred over the
connection as a stream of octets prepended with a four octet field in connection as a stream of octets prepended with a four octet field in
network byte order that represents the length of the following network byte order that represents the length of the following
buffer. The length of the security encoded data buffer MUST be no buffer. The length of the security encoded data buffer MUST be no
larger than the maximum size that was either defined in the mechanism larger than the maximum size that was either defined in the mechanism
specification or negotiated by the other side during the specification or negotiated by the other side during the
authentication protocol exchange. Upon the receipt of a data buffer authentication protocol exchange. Upon the receipt of a data buffer
which is larger than the defined/negotiated maximal buffer size, the which is larger than the defined/negotiated maximal buffer size, the
receiver SHOULD close the connection. This might be a sign of an receiver SHOULD close the connection. This might be a sign of an
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The registry is available at the URL The registry is available at the URL
"http://www.iana.org/assignments/gssapi-service-names" A definition "http://www.iana.org/assignments/gssapi-service-names" A definition
of the command to initiate the authentication protocol exchange. of the command to initiate the authentication protocol exchange.
This command must have as a parameter the name of the mechanism being This command must have as a parameter the name of the mechanism being
selected by the client. selected by the client.
The command SHOULD have an optional parameter giving an initial The command SHOULD have an optional parameter giving an initial
response. This optional parameter allows the client to avoid a round response. This optional parameter allows the client to avoid a round
trip when using a mechanism which is defined to have the client send 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 data first. When this initial response is sent by the client and the
selected mechanism is defined to have the server start with an
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selected mechanism is defined to have the server start with an
initial challenge, the command fails. See section 6.1 of this initial challenge, the command fails. See section 6.1 of this
document for further information. A definition of the method by document for further information. A definition of the method by
which the authentication protocol exchange is carried out, including which the authentication protocol exchange is carried out, including
how the challenges and responses are encoded, how the server how the challenges and responses are encoded, how the server
indicates completion or failure of the exchange, how the client indicates completion or failure of the exchange, how the client
aborts an exchange, and how the exchange method interacts with any aborts an exchange, and how the exchange method interacts with any
line length limits in the protocol. line length limits in the protocol.
The command SHOULD have a method for the server to include an The command SHOULD have a method for the server to include an
optional challenge with a success notification. This allows the optional challenge with a success notification. This allows the
server to avoid a round trip when using a mechanism which is defined server to avoid a round trip when using a mechanism which is defined
to have the server send additional data along with the indication of to have the server send additional data along with the indication of
successful completion. See section 6.2 of this document for further successful completion. See section 6.2 of this document for further
information. information.
Identification of the octet where any negotiated security layer Identification of the octet where any negotiated security layer
starts to take effect, in both directions. starts to take effect, in both directions.
If both TLS and SASL security layer are allowed to be negotiated by
the protocol, the protocol profile MUST define in which order they
are applied to a cleartext data sent over the connection.
In addition, a protocol profile SHOULD specify a mechanism through In addition, a protocol profile SHOULD specify a mechanism through
which a client may obtain the names of the SASL mechanisms available which a client may obtain the names of the SASL mechanisms available
to it. This is typically done through the protocol's extensions or to it. This is typically done through the protocol's extensions or
capabilities mechanism. capabilities mechanism.
A protocol profile MAY further refine the definition of an A protocol profile MAY further refine the definition of an
authorization identity by adding additional syntactic restrictions authorization identity by adding additional syntactic restrictions
and protocol-specific semantics. and protocol-specific semantics. A protocol profile MUST specify the
form of the authorization identity (as it is protocol specific, as
opposed to the authentication identity which is mechanism specific)
and how authorization identities are to be compared. Profiles whose
authorization identities are simple user names (e.g. IMAP [RFC 3501])
are encouraged to employ [SASLPrep] profile [SASLPrep] of the
"stringprep" algorithm [StringPrep] to prepare these names for
matching.
<<State if the protocol profile supports realms?>>
A protocol profile SHOULD NOT attempt to amend the definition of A protocol profile SHOULD NOT attempt to amend the definition of
mechanisms or make mechanism-specific encodings. This breaks the mechanisms or make mechanism-specific encodings. This breaks the
separation between protocol and mechanism that is fundamental to the separation between protocol and mechanism that is fundamental to the
design of SASL. design of SASL.
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6. Specific issues 6. Specific issues
6.1. Client sends data first 6.1. Client sends data first
Some mechanisms specify that the first data sent in the Some mechanisms specify that the first data sent in the
authentication protocol exchange is from the client to the server. authentication protocol exchange is from the client to the server.
If a protocol's profile permits the command which initiates an If a protocol's profile permits the command which initiates an
authentication protocol exchange to contain an initial client authentication protocol exchange to contain an initial client
response, this parameter SHOULD be used with such mechanisms. response, this parameter SHOULD be used with such mechanisms.
If the initial client response parameter is not given, or if a If the initial client response parameter is not given, or if a
protocol's profile does not permit the command which initiates an protocol's profile does not permit the command which initiates an
authentication protocol exchange to contain an initial client authentication protocol exchange to contain an initial client
response, then the server issues a challenge with no data. The response, then the server issues a challenge with no data. The
client's response to this challenge is then used as the initial client's response to this challenge is then used as the initial
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client response. (The server then proceeds to send the next client response. (The server then proceeds to send the next
challenge, indicates completion, or indicates failure.) challenge, indicates completion, or indicates failure.)
6.2. Server returns success with additional data 6.2. Server returns success with additional data
Some mechanisms may specify that additional data be sent to the Some mechanisms may specify that additional data be sent to the
client along with an indication of successful completion of the client along with an indication of successful completion of the
exchange. This data would, for example, authenticate the server to exchange. This data would, for example, authenticate the server to
the client. the client.
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situation can happen when the server has a bug and produces the wrong situation can happen when the server has a bug and produces the wrong
response). After checking the data the client will think that the response). After checking the data the client will think that the
authentication exchange has failed, however the server will think authentication exchange has failed, however the server will think
that the authentication exchange has completed successfully. At this that the authentication exchange has completed successfully. At this
point the client can't abort the authentication exchange, it SHOULD point the client can't abort the authentication exchange, it SHOULD
close the connection instead. However if the profile didn't support close the connection instead. However if the profile didn't support
sending of additional data with success, the client could have sending of additional data with success, the client could have
aborted the exchange. aborted the exchange.
<<Should I add a flow diagram here or is it clear from the <<Should I add a flow diagram here or is it clear from the
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description?>> description?>>
6.3. Multiple authentications 6.3. Multiple authentications
Unless otherwise stated by the protocol's profile, only one Unless otherwise stated by the protocol's profile, only one
successful SASL negotiation may occur in a protocol session. In this successful SASL negotiation may occur in a protocol session. In this
case, once an authentication protocol exchange has successfully case, once an authentication protocol exchange has successfully
completed, further attempts to initiate an authentication protocol completed, further attempts to initiate an authentication protocol
exchange fail. exchange fail.
In the case that a profile explicitly permits multiple successful In the case that a profile explicitly permits multiple successful
SASL negotiations to occur, then in no case may multiple security SASL negotiations to occur, then in no case may multiple security
layers be simultaneously in effect. If a security layer is in effect layers be simultaneously in effect. If a security layer is in effect
and a subsequent SASL negotiation selects no security layer, the and a subsequent SASL negotiation selects a second security layer,
original security layer remains in effect. If a security layer is in then the second security layer replaces the first. If a security
effect and a subsequent SASL negotiation selects a second security layer is in effect and a subsequent SASL negotiation selects no
security layer, the original security layer must be removed. The next
paragraph explains why this is important.
Internet DRAFT SASL 18 May 2003 A security layer that remains in effect when a client, which already
has authenticated and established the security layer with "Realm A",
authenticates to "Realm B", without negotiating a new security layer,
enables "Realm B" to make guesses about previously observed
ciphertext using the web server's SASL engine as an oracle. "Realm
B" may observe how known cleartext is encrypted.
layer, then the second security layer replaces the first. <<Is this too specific to HTTP SASL profile? Probably not, the same
can happen when there is a proxy/frontend talking to different
servers/backends. Should be reworked not to reference "realm"?>>
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+---------+ +---------+
| | | |
| Realm B | | Realm A |
| | | |
+---------+ +---------+
| ^ |
| : +-----------+ |
Traffic from | : | Encryption| | Traffic from A
B to client +-------->| end point |<-------+ to client
: | (SSL/SASL)|
: +-----------+
: |
: |
: +---+
: | |
: | |
: | | Encryption tunnel, e.g. SASL or SSL,
: | | between the server
(1) Recording +---------:| | and a single client only.
encrypted | | Separate tunnels to different
traffic between | | clients.
Realm A and client +---+
|
|
+-----------> Traffic to clients
7. The EXTERNAL mechanism 7. The EXTERNAL mechanism
The mechanism name associated with external authentication is The mechanism name associated with external authentication is
"EXTERNAL". "EXTERNAL".
The client sends an initial response with the UTF-8 encoding of the The client sends an initial response with the UTF-8 encoding of the
authorization identity. The form of the authorization identity is authorization identity. The form of the authorization identity is
further restricted by the application-level protocol's SASL profile. further restricted by the application-level protocol's SASL profile.
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successful completion of the authentication exchange; otherwise the successful completion of the authentication exchange; otherwise the
server indicates failure. server indicates failure.
The system providing this external information may be, for example, The system providing this external information may be, for example,
IPsec or TLS. IPsec or TLS.
If the client sends the empty string as the authorization identity If the client sends the empty string as the authorization identity
(thus requesting the authorization identity be derived from the (thus requesting the authorization identity be derived from the
client's authentication credentials), the authorization identity is client's authentication credentials), the authorization identity is
to be derived from authentication credentials which exist in the to be derived from authentication credentials which exist in the
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system which is providing the external authentication. system which is providing the external authentication.
7.1. Formal syntax 7.1. Formal syntax
The following syntax specification uses the augmented Backus-Naur The following syntax specification uses the augmented Backus-Naur
Form (BNF) notation as specified in [ABNF]. This uses the ABNF core Form (BNF) notation as specified in [ABNF]. This uses the ABNF core
rules as specified in Appendix A of the ABNF specification [ABNF]. rules as specified in Appendix A of the ABNF specification [ABNF].
Non-terminals referenced but not defined below are as defined by Non-terminals referenced but not defined below are as defined by
[UTF-8]. [UTF-8].
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initial-response = *( UTF8-char-no-null ) initial-response = *( UTF8-char-no-null )
UTF8-char-no-null = UTF8-1-no-null / UTF8-2 / UTF8-3 / UTF8-4 UTF8-char-no-null = UTF8-1-no-null / UTF8-2 / UTF8-3 / UTF8-4
UTF8-1-no-null = %x01-7F UTF8-1-no-null = %x01-7F
7.2. Example 7.2. Example
The following is an example of an EXTERNAL authentication in the SMTP The following is an example of an EXTERNAL authentication in the SMTP
protocol [SMTP-AUTH]. In this example, the client is proxy protocol [SMTP-AUTH]. In this example, the client is proxy
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authenticating, sending the authorization id "fred". The server has authenticating, sending the authorization id "fred". The server has
determined the client's identity through IPsec and has a security determined the client's identity through IPsec and has a security
policy that permits that identity to proxy authenticate as any other policy that permits that identity to proxy authenticate as any other
identity. identity.
To the protocol profile, the four octet sequence "fred" is an opaque To the protocol profile, the four octet sequence "fred" is an opaque
binary blob. The SASL protocol profile for SMTP specifies that binary blob. The SASL protocol profile for SMTP specifies that
server challenges and client responses are encoded in BASE64; the server challenges and client responses are encoded in BASE64; the
BASE64 encoding of "fred" is "ZnJlZA==". BASE64 encoding of "fred" is "ZnJlZA==".
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C: AUTH EXTERNAL ZnJlZA== C: AUTH EXTERNAL ZnJlZA==
S: 235 Authentication successful. S: 235 Authentication successful.
8. IANA Considerations 8. IANA Considerations
Registration of a SASL mechanism is done by filling in the template Registration of a SASL mechanism is done by filling in the template
in section 8.4 and sending it in to iana@iana.org. IANA has the in section 8.4 and sending it in to iana@iana.org. IANA has the
right to reject obviously bogus registrations, but will perform no right to reject obviously bogus registrations, but will perform no
review of claims made in the registration form. review of claims made in the registration form.
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There is no naming convention for SASL mechanisms; any name that There is no naming convention for SASL mechanisms; any name that
conforms to the syntax of a SASL mechanism name can be registered. conforms to the syntax of a SASL mechanism name can be registered.
An IETF Standards Track document may reserve a portion of the SASL An IETF Standards Track document may reserve a portion of the SASL
mechanism namespace for its own use, amending the registration rules mechanism namespace for its own use, amending the registration rules
for that portion of the namespace. for that portion of the namespace.
While the registration procedures do not require it, authors of SASL While the registration procedures do not require it, authors of SASL
mechanisms are encouraged to seek community review and comment mechanisms are encouraged to seek community review and comment
whenever that is feasible. Authors may seek community review by whenever that is feasible. Authors may seek community review by
posting a specification of their proposed mechanism as an internet- posting a specification of their proposed mechanism as an internet-
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8.1. Comments on SASL mechanism registrations 8.1. Comments on SASL mechanism registrations
Comments on registered SASL mechanisms should first be sent to the Comments on registered SASL mechanisms should first be sent to the
"owner" of the mechanism. Submitters of comments may, after a "owner" of the mechanism. Submitters of comments may, after a
reasonable attempt to contact the owner, request IANA to attach their reasonable attempt to contact the owner, request IANA to attach their
comment to the SASL mechanism registration itself. If IANA approves comment to the SASL mechanism registration itself. If IANA approves
of this the comment will be made accessible in conjunction with the of this the comment will be made accessible in conjunction with the
SASL mechanism registration itself. SASL mechanism registration itself.
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8.2. Location of registered SASL mechanism list 8.2. Location of registered SASL mechanism list
SASL mechanism registrations are available at the URL SASL mechanism registrations are available at the URL
"http://www.iana.org/assignments/sasl-mechanisms" The SASL mechanism "http://www.iana.org/assignments/sasl-mechanisms" The SASL mechanism
description and other supporting material may also be published as an description and other supporting material may also be published as an
Informational RFC by sending it to "rfc-editor@rfc-editor.org" Informational RFC by sending it to "rfc-editor@rfc-editor.org"
(please follow the instructions to RFC authors [RFC-INSTRUCTIONS]). (please follow the instructions to RFC authors [RFC-INSTRUCTIONS]).
8.3. Change control 8.3. Change control
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done without discussion or review. done without discussion or review.
The IESG may reassign responsibility for a SASL mechanism. The most The IESG may reassign responsibility for a SASL mechanism. The most
common case of this will be to enable changes to be made to common case of this will be to enable changes to be made to
mechanisms where the author of the registration has died, moved out mechanisms where the author of the registration has died, moved out
of contact or is otherwise unable to make changes that are important of contact or is otherwise unable to make changes that are important
to the community. to the community.
SASL mechanism registrations may not be deleted; mechanisms which are SASL mechanism registrations may not be deleted; mechanisms which are
no longer believed appropriate for use can be declared OBSOLETE by a no longer believed appropriate for use can be declared OBSOLETE by a
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change to their "intended use" field; such SASL mechanisms will be change to their "intended use" field; such SASL mechanisms will be
clearly marked in the lists published by IANA. clearly marked in the lists published by IANA.
The IESG is considered to be the owner of all SASL mechanisms which The IESG is considered to be the owner of all SASL mechanisms which
are on the IETF standards track. are on the IETF standards track.
8.4. Registration template 8.4. Registration template
To: iana@isi.edu To: iana@isi.edu
Subject: Registration of SASL mechanism X Subject: Registration of SASL mechanism X
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Security considerations: Security considerations:
Published specification (optional, recommended): Published specification (optional, recommended):
Person & email address to contact for further information: Person & email address to contact for further information:
Intended usage: Intended usage:
(One of COMMON, LIMITED USE or OBSOLETE) (One of COMMON, LIMITED USE or OBSOLETE)
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Owner/Change controller: Owner/Change controller:
(Any other information that the author deems interesting may be (Any other information that the author deems interesting may be
added below this line.) added below this line.)
8.5. The EXTERNAL mechanism registration 8.5. The EXTERNAL mechanism registration
It is requested that the SASL Mechanism registry [IANA-SASL] entry It is requested that the SASL Mechanism registry [IANA-SASL] entry
for the EXTERNAL mechanism be updated to reflect that this document for the EXTERNAL mechanism be updated to reflect that this document
now provides its technical specification. now provides its technical specification.
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To: iana@iana.org Subject: Updated Registration of SASL mechanism To: iana@iana.org Subject: Updated Registration of SASL mechanism
EXTERNAL EXTERNAL
SASL mechanism name: EXTERNAL SASL mechanism name: EXTERNAL
Security considerations: See RFC XXXX, section 10. Security considerations: See RFC XXXX, section 10.
Published specification (optional, recommended): RFC XXXX Published specification (optional, recommended): RFC XXXX
Person & email address to contact for further information: Person & email address to contact for further information:
Alexey Melnikov <mel@messagingdirect.com> Alexey Melnikov <mel@isode.com>
Intended usage: COMMON Intended usage: COMMON
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Owner/Change controller: IESG <iesg@ietf.org> Owner/Change controller: IESG <iesg@ietf.org>
Note: Updates existing entry for EXTERNAL Note: Updates existing entry for EXTERNAL
9. References 9. References
9.1. Normative References 9.1. Normative References
[ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications: [ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications:
ABNF", RFC 2234, November 1997 ABNF", RFC 2234, November 1997
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[GSSAPI] Linn, "Generic Security Service Application Program [GSSAPI] Linn, "Generic Security Service Application Program
Interface, Version 2, Update 1", RFC 2743, January 2000 Interface, Version 2, Update 1", RFC 2743, January 2000
[ISO-10646] "Universal Multiple-Octet Coded Character Set (UCS) - [ISO-10646] "Universal Multiple-Octet Coded Character Set (UCS) -
Architecture and Basic Multilingual Plane", ISO/IEC 10646-1 : 1993. Architecture and Basic Multilingual Plane", ISO/IEC 10646-1 : 1993.
[KEYWORDS] Bradner, "Key words for use in RFCs to Indicate [KEYWORDS] Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997 Requirement Levels", RFC 2119, March 1997
Internet DRAFT SASL 18 May 2003
[Stringprep] P. Hoffman, M. Blanchet, "Preparation of [Stringprep] P. Hoffman, M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")", RFC 3454, December 2002. Internationalized Strings ("stringprep")", RFC 3454, December 2002.
[SASLPrep] Zeilenga, K., "SASLprep: Stringprep profile for user names [SASLPrep] Zeilenga, K., "SASLprep: Stringprep profile for user names
and passwords", Work in progress, draft-ietf-sasl-saslprep-XX.txt. and passwords", Work in progress, draft-ietf-sasl-saslprep-XX.txt.
[UNICODE-NORMALIZATION] Davis, Durst, "Unicode Standard Annex #15:
Unicode Normalization Forms", March 2001,
http://www.unicode.org/unicode/reports/tr15/
[UTF-8] Yergeau, "UTF-8, a transformation format of ISO 10646", work [UTF-8] Yergeau, "UTF-8, a transformation format of ISO 10646", work
in progress (draft-yergeau-rfc2279bis-XX) that replaces RFC 2279, in progress (draft-yergeau-rfc2279bis-XX) that replaces RFC 2279,
Janyary 1998 Janyary 1998
9.2. Informative References 9.2. Informative References
<<Update the reference below>> [SASL-GSSAPI] Myers, "SASL GSSAPI <<Update the reference below>> [SASL-GSSAPI] Myers, "SASL GSSAPI
mechanisms", draft-ietf-cat-sasl-gssapi-XX.txt, September 2000 mechanisms", draft-ietf-cat-sasl-gssapi-XX.txt, September 2000
[SASL-OTP] Newman, "The One-Time-Password SASL Mechanism", RFC 2444, [SASL-OTP] Newman, "The One-Time-Password SASL Mechanism", RFC 2444,
October 1998 October 1998
[SMTP-AUTH] Myers, "SMTP Service Extension for Authentication", RFC [SMTP-AUTH] Myers, "SMTP Service Extension for Authentication", RFC
2554, March 1999 2554, March 1999
[RFC-INSTRUCTIONS] Postel, Reynolds, "Instructions to RFC Authors", [RFC-INSTRUCTIONS] Postel, Reynolds, "Instructions to RFC Authors",
RFC 2223, October 1997 RFC 2223, October 1997
[IANA-SASL] IANA, "SIMPLE AUTHENTICATION AND SECURITY LAYER (SASL) [IANA-SASL] IANA, "SIMPLE AUTHENTICATION AND SECURITY LAYER (SASL)
Internet DRAFT SASL 27 June 2003
MECHANISMS", http://www.iana.org/assignments/sasl-mechanisms. MECHANISMS", http://www.iana.org/assignments/sasl-mechanisms.
10. Security considerations 10. Security considerations
Security issues are discussed throughout this memo. Security issues are discussed throughout this memo.
The mechanisms that support integrity protection are designed such The mechanisms that support integrity protection are designed such
that the negotiation of the security layer and authorization identity that the negotiation of the security layer and authorization identity
is integrity protected. When the client selects a security layer is integrity protected. When the client selects a security layer
with at least integrity protection, this protects against an active with at least integrity protection, this protects against an active
attacker hijacking the connection and modifying the authentication attacker hijacking the connection and modifying the authentication
exchange to negotiate a plaintext connection. exchange to negotiate a plaintext connection.
When a server or client supports multiple authentication mechanisms, When a server or client supports multiple authentication mechanisms,
each of which has a different security strength, it is possible for 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 an active attacker to cause a party to use the least secure mechanism
supported. To protect against this sort of attack, a client or supported. To protect against this sort of attack, a client or
server which supports mechanisms of different strengths should have a server which supports mechanisms of different strengths should have a
configurable minimum strength that it will use. It is not sufficient configurable minimum strength that it will use. It is not sufficient
Internet DRAFT SASL 18 May 2003
for this minimum strength check to only be on the server, since an for this minimum strength check to only be on the server, since an
active attacker can change which mechanisms the client sees as being active attacker can change which mechanisms the client sees as being
supported, causing the client to send authentication credentials for supported, causing the client to send authentication credentials for
its weakest supported mechanism. its weakest supported mechanism.
The client's selection of a SASL mechanism is done in the clear and 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 may be modified by an active attacker. It is important for any new
SASL mechanisms to be designed such that an active attacker cannot SASL mechanisms to be designed such that an active attacker cannot
obtain an authentication with weaker security properties by modifying obtain an authentication with weaker security properties by modifying
the SASL mechanism name and/or the challenges and responses. the SASL mechanism name and/or the challenges and responses.
skipping to change at page 14, line 37 skipping to change at page 16, line 5
protocol exchange, the receiver should handle gracefully any security protocol exchange, the receiver should handle gracefully any security
encoded data buffer larger than the defined/negotiated maximal size. encoded data buffer larger than the defined/negotiated maximal size.
In particular, it must not blindly allocate the ammount of memory In particular, it must not blindly allocate the ammount of memory
specified in the buffer size field, as this might cause the "out of specified in the buffer size field, as this might cause the "out of
memory" condition. If the receiver detects a large block, it SHOULD memory" condition. If the receiver detects a large block, it SHOULD
close the connection. close the connection.
"stringprep" and Unicode security considerations apply to "stringprep" and Unicode security considerations apply to
authentication identities, authorization identities and passwords. authentication identities, authorization identities and passwords.
Internet DRAFT SASL 27 June 2003
The EXTERNAL mechanism provides no security protection; it is The EXTERNAL mechanism provides no security protection; it is
vulnerable to spoofing by either client or server, active attack, and vulnerable to spoofing by either client or server, active attack, and
eavesdropping. It should only be used when external security eavesdropping. It should only be used when external security
mechanisms are present and have sufficient strength. mechanisms are present and have sufficient strength.
11. Editor's Address 11. Editor's Address
Alexey Melnikov Alexey Melnikov
ACI Worldwide/MessagingDirect Isode
Email: mel@messagingdirect.com Email: mel@isode.com
12. Acknowledgments 12. Acknowledgments
This document is a revision of RFC 2222 written by John G. Myers This document is a revision of RFC 2222 written by John G. Myers
<jgmyers@netscape.com>. He also wrote the major part of this <jgmyers@netscape.com>. He also wrote the major part of this
document. document.
Internet DRAFT SASL 18 May 2003 Thank you to Magnus Nystrom for the ASCII picture used in section
6.3.
<<Other people reviewed this document too. Mention some names?>>
13. Full Copyright Statement 13. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are kind, provided that the above copyright notice and this paragraph are
skipping to change at page 15, line 31 skipping to change at page 17, line 4
copyrights defined in the Internet Standards process must be copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than followed, or as required to translate it into languages other than
English. English.
The limited permissions granted above are perpetual and will not be The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
Internet DRAFT SASL 27 June 2003
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement Acknowledgement
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
Appendix A. Relation of SASL to transport security Appendix A. Relation of SASL to transport security
skipping to change at page 16, line 4 skipping to change at page 17, line 31
Two of the key features of SASL are: Two of the key features of SASL are:
The separation of the authorization identity from the identity in The separation of the authorization identity from the identity in
the client's credentials. This permits agents such as proxy the client's credentials. This permits agents such as proxy
servers to authenticate using their own credentials, yet request servers to authenticate using their own credentials, yet request
the access privileges of the identity for which they are proxying. the access privileges of the identity for which they are proxying.
Upon successful completion of an authentication exchange, the Upon successful completion of an authentication exchange, the
server knows the authorization identity the client wishes to use. server knows the authorization identity the client wishes to use.
Internet DRAFT SASL 18 May 2003
This allows servers to move to a "user is authenticated" state in This allows servers to move to a "user is authenticated" state in
the protocol. the protocol.
These features are extremely important to some application protocols, These features are extremely important to some application protocols,
yet Transport Security services do not always provide them. To yet Transport Security services do not always provide them. To
define SASL mechanisms based on these services would be a very messy define SASL mechanisms based on these services would be a very messy
task, as the framing of these services would be redundant with the task, as the framing of these services would be redundant with the
framing of SASL and some method of providing these important SASL framing of SASL and some method of providing these important SASL
features would have to be devised. features would have to be devised.
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the scope of SASL, and should be different from the command which the scope of SASL, and should be different from the command which
starts a SASL authentication protocol exchange. starts a SASL authentication protocol exchange.
In certain situations, it is reasonable to use SASL underneath one of In certain situations, it is reasonable to use SASL underneath one of
these Transport Security services. The transport service would these Transport Security services. The transport service would
secure the connection, either service would authenticate the client, secure the connection, either service would authenticate the client,
and SASL would negotiate the authorization identity. The SASL and SASL would negotiate the authorization identity. The SASL
negotiation would be what moves the protocol from "unauthenticated" negotiation would be what moves the protocol from "unauthenticated"
to "authenticated" state. The "EXTERNAL" SASL mechanism is to "authenticated" state. The "EXTERNAL" SASL mechanism is
explicitly intended to handle the case where the transport service explicitly intended to handle the case where the transport service
Internet DRAFT SASL 27 June 2003
secures the connection and authenticates the client and SASL secures the connection and authenticates the client and SASL
negotiates the authorization identity. negotiates the authorization identity.
When using SASL underneath a sufficiently strong Transport Security When using SASL underneath a sufficiently strong Transport Security
service, a SASL security layer would most likely be redundant. The service, a SASL security layer would most likely be redundant. The
client and server would thus probably want to negotiate off the use client and server would thus probably want to negotiate off the use
of a SASL security layer. of a SASL security layer.
Appendix B. IANA considerations Appendix B. IANA considerations
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of the EXTERNAL mechanism to this document. of the EXTERNAL mechanism to this document.
Appendix C. Changes since RFC 2222 Appendix C. Changes since RFC 2222
The GSSAPI mechanism was removed. It is now specified in a separate The GSSAPI mechanism was removed. It is now specified in a separate
document [SASL-GSSAPI]. document [SASL-GSSAPI].
The "KERBEROS_V4" mechanism defined in RFC 2222 is obsolete and has The "KERBEROS_V4" mechanism defined in RFC 2222 is obsolete and has
been removed. been removed.
Internet DRAFT SASL 18 May 2003
The "SKEY" mechanism described in RFC 2222 is obsolete and has been The "SKEY" mechanism described in RFC 2222 is obsolete and has been
removed. It has been replaced by the OTP mechanism [SASL-OTP]. removed. It has been replaced by the OTP mechanism [SASL-OTP].
The overview has been substantially reorganized and clarified. The overview has been substantially reorganized and clarified.
Clarified the definition and semantics of the authorization identity. Clarified the definition and semantics of the authorization identity.
Prohibited the NULL character in authorization identities. Prohibited the NULL character in authorization identities.
Added a section on character string issues. Added a section on character string issues.
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Specified that protocol profiles SHOULD provide a way for clients to Specified that protocol profiles SHOULD provide a way for clients to
discover available SASL mechanisms. discover available SASL mechanisms.
Made the requirement that protocol profiles specify the semantics of Made the requirement that protocol profiles specify the semantics of
the authorization identity optional to the protocol profile. the authorization identity optional to the protocol profile.
Clarified that such a specification is a refinement of the definition Clarified that such a specification is a refinement of the definition
in the base SASL spec. in the base SASL spec.
Added a requirement discouraging protocol profiles from breaking the Added a requirement discouraging protocol profiles from breaking the
Internet DRAFT SASL 27 June 2003
separation between protocol and mechanism. separation between protocol and mechanism.
Mentioned that standards track documents may carve out their own Mentioned that standards track documents may carve out their own
portions of the SASL mechanism namespace. portions of the SASL mechanism namespace.
Specified that the authorization identity in the EXTERNAL mechanism Specified that the authorization identity in the EXTERNAL mechanism
is encoded in UTF-8. is encoded in UTF-8.
Added a statement that a protocol profile SHOULD allow challenge data Added a statement that a protocol profile SHOULD allow challenge data
to be sent with a success indication. to be sent with a success indication.
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Updated IANA related URLs. Updated IANA related URLs.
Updated references and split them into Informative and Normative. Updated references and split them into Informative and Normative.
Added text to the Security Considerations section regarding handling Added text to the Security Considerations section regarding handling
of extremely large SASL blocks. of extremely large SASL blocks.
Replaced UTF-8 ABNF with the reference to the UTF-8 document. Replaced UTF-8 ABNF with the reference to the UTF-8 document.
Added text about SASLPrep for authentication identities and Added text about SASLPrep for authentication identities and
Internet DRAFT SASL 18 May 2003
passwords. passwords.
Added paragraph about verifying authorization identities. Added paragraph about verifying authorization identities.
Internet DRAFT SASL 18 May 2003 This document requires to drop a security layer on reauthentication
when no security layer is negotiated. This differs from RFC 2222,
which required to keep the last security layer in this case.
Added a protocol profile requirement to specify interaction between
SASL and TLS security layers.
Internet DRAFT SASL 27 June 2003
Table of contents Table of contents
Status of this Memo .......................................... i Status of this Memo .......................................... i
1. Abstract ............................................... 2 1. Abstract ............................................... 2
2. Organization of this document .......................... 2 2. Organization of this document .......................... 2
2.1. How to read this document .............................. 2 2.1. How to read this document .............................. 2
2.2. Conventions used in this document ...................... 2 2.2. Conventions used in this document ...................... 2
3. Overview ............................................... 2 3. Overview ............................................... 2
4. Authentication mechanisms .............................. 3 4. Authentication mechanisms .............................. 3
4.1. Authentication protocol exchange ....................... 4 4.1. Authentication protocol exchange ....................... 4
4.2. Authorization identities and proxy authentication ...... 4 4.2. Authorization identities and proxy authentication ...... 4
4.3. Security layers ........................................ 5 4.3. Security layers ........................................ 5
4.4. Character string issues ................................ 6 4.4. Character string issues ................................ 6
5. Protocol profile requirements .......................... 6 5. Protocol profile requirements .......................... 6
6. Specific issues ........................................ 7 6. Specific issues ........................................ 8
6.1. Client sends data first ................................ 7 6.1. Client sends data first ................................ 8
6.2. Server returns success with additional data ............ 8 6.2. Server returns success with additional data ............ 8
6.3. Multiple authentications ............................... 8 6.3. Multiple authentications ............................... 9
7. The EXTERNAL mechanism ................................. 9 7. The EXTERNAL mechanism ................................ 10
7.1. Formal syntax .......................................... 9 7.1. Formal syntax ......................................... 11
7.2. Example ................................................ 9 7.2. Example ............................................... 11
8. IANA Considerations ................................... 10 8. IANA Considerations ................................... 11
8.1. Comments on SASL mechanism registrations .............. 10 8.1. Comments on SASL mechanism registrations .............. 12
8.2. Location of registered SASL mechanism list ............ 11 8.2. Location of registered SASL mechanism list ............ 12
8.3. Change control ........................................ 11 8.3. Change control ........................................ 12
8.4. Registration template ................................. 11 8.4. Registration template ................................. 13
8.5. The EXTERNAL mechanism registration ................... 12 8.5. The EXTERNAL mechanism registration ................... 13
9. References ............................................ 12 9. References ............................................ 14
9.1. Normative References .................................. 12 9.1. Normative References .................................. 14
9.2. Informative References ................................ 13 9.2. Informative References ................................ 14
10. Security considerations ............................... 13 10. Security considerations ............................... 15
11. Editor's Address ...................................... 14 11. Editor's Address ...................................... 16
12. Acknowledgments ....................................... 14 12. Acknowledgments ....................................... 16
13. Full Copyright Statement .............................. 15 13. Full Copyright Statement .............................. 16
Appendix A. Relation of SASL to transport security .......... 15 Appendix A. Relation of SASL to transport security .......... 17
Appendix B. IANA considerations ............................. 16 Appendix B. IANA considerations ............................. 18
Appendix C. Changes since RFC 2222 .......................... 16 Appendix C. Changes since RFC 2222 .......................... 18
 End of changes. 

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