Internet DRAFT - draft-melnikov-sasl2
draft-melnikov-sasl2
Network Working Group D. Cridland
Internet-Draft
Intended status: Standards Track T. Molitor
Expires: 25 April 2024
M. Wild
A. Melnikov
Isode Ltd
23 October 2023
Extensible Simple Authentication and Security Layer (SASL)
draft-melnikov-sasl2-01
Abstract
The Simple Authentication and Security Layer (SASL) is a framework
for providing authentication and data security services in
connection-oriented protocols via replaceable mechanisms. It
provides a structured interface between protocols and mechanisms.
The resulting framework allows new protocols to reuse existing
mechanisms and allows old protocols to make use of new mechanisms.
The framework also provides a protocol for securing subsequent
protocol exchanges within a data security layer.
This document describes how a SASL mechanism is structured, describes
how protocols include support for SASL, and defines the protocol for
carrying a data security layer over a connection. This document also
defines how servers can request fulfillment of extra authentication
related tasks, such as two factor authentication and/or password
change.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 25 April 2024.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Channel Binding advertisement . . . . . . . . . . . . . . . . 6
5. Extra Protocol Requirements . . . . . . . . . . . . . . . . . 7
6. Extra Mechanism Requirements . . . . . . . . . . . . . . . . 8
7. Example of a Protocol fulfilling extra requirements . . . . . 8
8. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
12.1. Normative References . . . . . . . . . . . . . . . . . . 9
12.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The Simple Authentication and Security Layer (SASL) is a framework
for providing authentication and data security services in
connection-oriented protocols via replaceable mechanisms. SASL
provides a structured interface between protocols and mechanisms.
SASL also provides a protocol for securing subsequent protocol
exchanges within a data security layer. The data security layer can
provide data integrity, data confidentiality, and other services.
SASL's design is intended to allow new protocols to reuse existing
mechanisms without requiring redesign of the mechanisms and allows
existing protocols to make use of new mechanisms without redesign of
protocols.
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SASL is conceptually a framework that provides an abstraction layer
between protocols and mechanisms as illustrated in the following
diagram.
SMTP LDAP XMPP Other protocols ...
\ | | /
\ | | /
SASL abstraction layer
/ | | \
/ | | \
EXTERNAL GSSAPI PLAIN Other mechanisms ...
It is through the interfaces of this abstraction layer that the
framework allows any protocol to utilize any mechanism. While this
layer does generally hide the particulars of protocols from
mechanisms and the particulars of mechanisms from protocols, this
layer does not generally hide the particulars of mechanisms from
protocol implementations. For example, different mechanisms require
different information to operate, some of them use password-based
authentication, some of then require realm information, others make
use of Kerberos tickets, certificates, etc. Also, in order to
perform authorization, server implementations generally have to
implement identity mapping between authentication identities, whose
form is mechanism specific, and authorization identities, whose form
is application protocol specific. Section 2 discusses identity
concepts.
It is possible to design and implement this framework in ways that do
abstract away particulars of similar mechanisms. Such a framework
implementation, as well as mechanisms implementations, could be
designed not only to be shared by multiple implementations of a
particular protocol but to be shared by implementations of multiple
protocols.
Since the publication of [RFC4422] a number of shortcomings in the
SASL framework were identified that are addressed in this document.
[[Note that the current draft only shows changes from RFC 4422.]]
This specification addresses a number of shortfalls in [RFC4422]:
* Support for Two-factor authentication (2FA) or Multi-factor
authentication (MFA) tasks.
* Support for mandatory password change tasks.
* Channel Binding advertisement.
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* Shared key derivation after successful authentication.
Extensions to SASL documented herein are primarily to allow for
better capability discovery, and additional results beyond total
success or abject failure.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Character names in this document use the notation for code points and
names from the Unicode Standard [Unicode]. For example, the letter
"a" may be represented as either <U+0061> or <LATIN SMALL LETTER A>.
Note: a glossary of terms used in Unicode can be found in [Glossary].
Information on the Unicode character encoding model can be found in
[CharModel].
Example lines prefaced by "C:" are sent by the client and ones
prefaced by "S:" by the server. If a single "C:" or "S:" label
applies to multiple lines, then the line breaks between those lines
are for editorial clarity only, and are not part of the actual
protocol exchange.
3. Tasks
A protocol profile might have a way to indicate that while the SASL
exchange was successful, it is insufficient to allow authentication
at this time. We call this indicator a "continue outcome message".
This can be used to indicate a need to execute extra task(s), for
example, that the Client needs to perform a Second Factor
Authentication ("2FA")and/or is required to change password (this
list is not meant to be exhaustive in any way).
These tasks are analogous to a SASL mechanism, but have a number of
differences - they may never attempt to negotiate a new authorization
identifier, nor a new security layer.
Each task has a name ([[need to define syntax and maximum length]])
that SHOULD be registered with IANA.
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A client MAY choose any one of the offered tasks; if multiple are
required, once a task is successfully completed, the server will
indicate that another one is required, and so on, until all mandatory
tasks are complete.
The continue outcome message MAY include SASL mechanism specific
additional data, as the successful outcome message does.
Finally, the continue outcome message MAY contain a textual data,
which contains human-readable data explaining the nature of the step
required.
Example 1. Continue Required (using XMPP protocol)
S: <continue xmlns='urn:xmpp:sasl:2'>
<additional-data>
SSdtIGJvcmVkIG5vdy4=
</additional-data>
<tasks>
<task>HOTP-EXAMPLE</task>
<task>TOTP-EXAMPLE</task>
</tasks>
<text>This account requires 2FA</text>
</continue>
If any SASL security layer was negotiated, it takes effect after the
final octet of the first continue outcome message.
Clients respond with a task initiation message, which has a single
mandatory parameter containing the selected task name, and MAY
contain any task specific data.
Each task MUST end either by the server sending a task failure
indicator message, if the task failed, a continue outcome message, if
the task was completed successfully and the server requests the
client to perform a new task, or a successful outcome message,
indicating that the task was completed successfully and no further
tasks are needed.
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Example 2. Fictional TOTP task
<!-- Client starts TOTP-EXAMPLE task -->
<next xmlns='urn:xmpp:sasl:2' task='TOTP-EXAMPLE'>
<totp xmlns="urn:totp:example">
SSd2ZSBydW4gb3V0IG9mIGlkZWFzIGhlcmUu
</totp>
</next>
<!-- Server provides needed data to Client -->
<task-data xmlns='urn:xmpp:sasl:2'>
<totp xmlns="urn:totp:example">
94d27acffa2e99a42ba7786162a9e73e7ab17b9d
</totp>
</task-data>
<!-- Client responds with requested TOP data -->
<task-data xmlns='urn:xmpp:sasl:2'>
<totp xmlns="urn:totp:example">
OTRkMjdhY2ZmYTJlOTlhNDJiYTc3ODYxNjJhOWU3M2U3YWIxN2I5ZAo=
</totp>
</task-data>
<!-- Server indicates successful completion of TOTP-EXAMPLE task -->
<success xmlns='urn:xmpp:sasl:2'>
<totp xmlns="urn:totp:example">
SGFkIHlvdSBnb2luZywgdGhlcmUsIGRpZG4ndCBJPw==
</totp>
<authorization-identifier>juliet@montague.example</authorization-identifier>
</success>
4. Channel Binding advertisement
Most modern SASL mechanism are expected to support channel bindings
[RFC5056].
Explicit advertisement of server supported channel binding types
improves interoperability and is also necessary to prevent certain
MITM attacks.
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Example 3. Channel Binding Type advertisement in XMPP (XEP-0440).
Note that the <sasl-channel-binding> element is the new channel
binding advertisement.
<stream:features>
<sasl-channel-binding xmlns='urn:xmpp:sasl-cb:0'>
<channel-binding type='tls-server-end-point'/>
<channel-binding type='tls-exporter'/>
</sasl-channel-binding>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>EXTERNAL</mechanism>
<mechanism>SCRAM-SHA-1-PLUS</mechanism>
<mechanism>PLAIN</mechanism>
</mechanisms>
</stream:features>
5. Extra Protocol Requirements
[[Note that the item number continues the numbering of requirements
from Section 4 of RFC 4422.]]
[[Alexey: All of the features below are optional (in order to remain
backward compatible with RFC 4422). However if any is implemented,
all of them MUST be implemented in a protocol. This makes client
implementations easier.]]
9) Facility to advertise the list of Channel Bindings that the
server supports. See Section 4.
10) Detail any task negotiation facility that the protocol
provides. [[Alexey: does this need to be done before
authentication starts, or is it sufficient to discover these at
the end of SASL mechanism exchange, when specific extra tasks are
requested?]] A protocol MUST specify a facility through which the
client may discover, the names of the SASL tasks that the server
makes available to the client. This facility is typically
provided through the protocol's extensions or capabilities
discovery facility (so that the client can be made aware of which
tasks might be required to complete authentication before starting
any authentication), as well as provided at the end of a SASL
authentication exchange.
11) Definition of the messages necessary for executing tasks,
including the following:
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a. A message to initiate execution of a task (see Section 3).
This message MUST contain a field for carrying the name of the
task selected by the client. This message MUST allow for an
optional field for carrying an initial task related data. The
specification MUST describe how messages with an empty initial
task related data are distinguished from messages with no
initial task related data. This field MUST be capable of
carrying arbitrary sequences of octets (including zero-length
sequences and sequences containing zero-valued octets).
b. Messages to transfer task related data from server and from
client (see Section 3). Each of these messages MUST be
capable of carrying arbitrary sequences of octets (including
zero-length sequences and sequences containing zero-valued
octets).
c. A message to indicate the outcome of the task execution and
whether or not execution of further tasks is required by the
server (see Section 3). This message MUST allow for an
optional field for carrying additional data with a successful
outcome. The specification MUST describe how messages with an
empty additional data are distinguished from messages with no
additional data. This field MUST be capable of carrying
arbitrary sequences of octets (including zero- length
sequences and sequences containing zero-valued octets).
6. Extra Mechanism Requirements
[[Note that the number continues the numbering of requirements from
Section 5 of RFC 4422.]]
6) Optional facility for SASL mechanism shared key derivation
after a successful authentication. .
7. Example of a Protocol fulfilling extra requirements
[[Ideally need 2 protocols. For example XMPP and IMAP. IMAP can
have a new command for tasks.]]
8. Open Issues
9. Security Considerations
TBD
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10. IANA Considerations
IANA is requested to create a new subregistry of "SASL tasks" for
registering SASL tasks as specified in this document.
The registration template is as follows:
Task Name: <need to define syntax!>
Task Type: <define the list of types and whether or not it will be extensible>
Pointer to specification text:
Notes (optional):
The registration procedure for the above registry is Expert Review.
11. Acknowledgements
TBD. Thank you XSF for XEP-0388, XEP-0440 and XEP-scram-upgrade.
12. References
12.1. Normative References
[CharModel]
Whistler, K. and A. Freytag, "Unicode character encoding
model", Unicode tr17, 11 November 2022,
<https://www.unicode.org/reports/tr17/>.
[Glossary] Consortium, U., "Glossary of Unicode Terms",
Unicode glossary, 2023,
<https://www.unicode.org/glossary/>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
Authentication and Security Layer (SASL)", RFC 4422,
DOI 10.17487/RFC4422, June 2006,
<https://www.rfc-editor.org/info/rfc4422>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
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[RFC5056] Williams, N., "On the Use of Channel Bindings to Secure
Channels", RFC 5056, DOI 10.17487/RFC5056, November 2007,
<https://www.rfc-editor.org/info/rfc5056>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[Unicode] Consortium, U., "Unicode 15.0.0", Unicode 15.0.0, 13
September 2022,
<https://www.unicode.org/versions/Unicode15.0.0/>.
12.2. Informative References
[RFC6238] M'Raihi, D., Machani, S., Pei, M., and J. Rydell, "TOTP:
Time-Based One-Time Password Algorithm", RFC 6238,
DOI 10.17487/RFC6238, May 2011,
<https://www.rfc-editor.org/info/rfc6238>.
Authors' Addresses
Dave Cridland
Email: dave@cridland.net
Thilo Molitor
Email: thilo+xmpp@eightysoft.de
Matthew Wild
Email: mwild1@gmail.com
Alexey Melnikov
Isode Ltd
Email: Alexey.Melnikov@isode.com
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