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Updated the documentation to include the latest version of
draft-ietf-kitten-scram-2fa in the set of LDAP-related
specifications.
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6 changes: 6 additions & 0 deletions docs/release-notes.html
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password storage scheme.
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Updated the documentation to include the latest version of
draft-ietf-kitten-scram-2fa in the set of LDAP-related specifications.
<br><br>
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</ul>

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146 changes: 73 additions & 73 deletions .../specs/draft-ietf-kitten-scram-2fa-02.txt → .../specs/draft-ietf-kitten-scram-2fa-03.txt
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Network Working Group A. Melnikov
Internet-Draft Isode Ltd
Intended status: Standards Track 13 January 2023
Expires: 17 July 2023
Intended status: Standards Track 24 August 2023
Expires: 25 February 2024


Extensions to Salted Challenge Response (SCRAM) for 2 factor
authentication
draft-ietf-kitten-scram-2fa-02
draft-ietf-kitten-scram-2fa-03

Abstract

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authentication. It also includes a separate extension for quick
reauthentication.

This specification also gives an example of how TOTP (RFC 6238) can
be used as the second factor.
This specification also gives 2 examples of second factors: TOTP (RFC
6238) and FIDO CTAP1/U2F.

Status of This Memo

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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on 17 July 2023.
This Internet-Draft will expire on 25 February 2024.

Copyright Notice

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and restrictions with respect to this document. Code Components
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2. Conventions Used in This Document

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

Formal syntax is defined by [RFC5234] including the core rules
defined in Appendix B of [RFC5234].
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server. This extension also doesn't cover enrollment with a 2FA
system, such enrollment happends out-of-band.

The server authenticates the client after receiving the second
message as described in Section 3 of [RFC5802] If the client included
"type" and "second-factor" attributes defined in this document (see
Section 5) and the server supports the specified second factor type,



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the server verifies content of the "second-factor" according to the
"type". If the second factor verification fails, the server MUST
fail authentication and SHOULD return either "replayed-second-factor"
or "invalid-second-factor" error in the "e" attribute. [[It would be
possible to make the extra attributes mandatory by using SCRAM's
"m=", but the text above doesn't do that. This is one of open issues
to resolve.]]
The server authenticates the client after receiving the second
message as described in Section 3 of [RFC5802]. If the client
included "type" and "second-factor" attributes defined in this
document (see Section 5) and the server supports the specified second
factor type, the server verifies content of the "second-factor"
according to the "type". If the second factor verification fails,
the server MUST fail authentication and SHOULD return either
"replayed-second-factor" or "invalid-second-factor" error in the "e"
attribute. [[It would be possible to make the extra attributes
mandatory by using SCRAM's "m=", but the text above doesn't do that.
This is one of open issues to resolve.]]

4. SCRAM Extension for reauthentication

This reauthentication extension to SCRAM allows the server to return
a token that can be used for quick reauthentication and bypasses 2
factor authentication prompt to the user. The reauthentication token
is a randomly generated value.The reauthentication token is returned
in the "o" attribute that is appended to the end of the "server-
final-message".
is a randomly generated value [RFC4086]. The reauthentication token
is returned in the "o" attribute that is appended to the end of the
"server-final-message".

[[Note: it would be possible to extend SCRAM itself to do
reauthentication, by including an earlier received reauthentication
Expand All @@ -202,11 +206,6 @@ Internet-Draft SCRAM 2FA extensions January 2023
[draft-schmaus-kitten-sasl-ht]). [[Note that the HT hash should
probably match the SCRAM hash used or "be better".]]

When the CLIENT-KEY/CLIENT-KEY-PLUS mechanism (see draft-cridland-
kitten-clientkey) is used for the reauthentication after a successful
SCRAM authentication, the reauthentication token is the Client Secret
Key. [[Need to also somehow convey token expiration?]]

5. Formal Syntax

This document defines the following new SCRAM attributes:
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* f: This attribute specifies the value of the second factor. For
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* t: This attribute specifies the type of second factor. For TOTP
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* l: base64-encoded challenge as returned by SCRAM server.

* f: This attribute specifies the value of the second factor. For
"t=ctap1" it is the CBOR-serialized value of
"t=ctap1" it is the CBOR-serialized [RFC8949] value of
authenticatorGetAssertionResponse map described below. This
attribute MUST be ignored unless the "t" attribute is also
specified.
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* Use clientDataHash parameter of [CTAP2] request as CTAP1/U2F
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Let authenticatorData is a byte string of following structure:
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9. Open Issues

Simon Josefsson: should this be a new SASL mechanism name, e.g.
CROTP-SHA-256?
CROTP-SHA-XXX?

Should we pick between TOTP and FIDO2 (CTAP1)?

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10. Security Considerations

Unless an external security layer (such as TLS) is also used, the OTP
value is sent in unencrypted/unhashed form from the client to the
server, which allows an attacker to read the OTP value and perform a
race with the server to validate the OTP.
An OTP value is a sensitive piece of data and thus should only be
sent over a secure channel (such as TLS). Otherwise an attacker
might be able to intercept it and reuse it for authentication to the
SCRAM server.

TBD



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11. IANA Considerations
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[draft-schmaus-kitten-sasl-ht]
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DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>.

[RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
Authentication and Security Layer (SASL)", RFC 4422,
DOI 10.17487/RFC4422, June 2006,
Expand All @@ -606,17 +611,25 @@ Internet-Draft SCRAM 2FA extensions January 2023
DOI 10.17487/RFC6238, May 2011,
<https://www.rfc-editor.org/info/rfc6238>.

[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011,
<https://www.rfc-editor.org/info/rfc6454>.


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[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011,
<https://www.rfc-editor.org/info/rfc6454>.

[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>.

[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.

[W3C_webauthn_3]
"Web Authentication: An API for accessing Public Key
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4 changes: 2 additions & 2 deletions docs/specs/internet-drafts.html
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</li>

<li>
<a href="draft-ietf-kitten-scram-2fa-02.txt">draft-ietf-kitten-scram-2fa-02</a>: Extensions to Salted Challenge Response (SCRAM) for 2 factor authentication
<a href="draft-ietf-kitten-scram-2fa-03.txt">draft-ietf-kitten-scram-2fa-03</a>: Extensions to Salted Challenge Response (SCRAM) for 2 factor authentication
<br>
Expiration Date: July 17, 2023
Expiration Date: February 25, 2024
<br><br>
</li>

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