Subject: Clarification required in RFC 2831 - DIGEST-MD5

From: Jonathan Bruce <[email-masked]>
Date: Wed, 20 Dec 2000 16:19:48 +0000

As part of the LDAPbis process there are a number of issues specifically related to RFC
2831 - 'Using Digest Authentication as a SASL Mechanism' that need to be clarified. Kurt
Zeilenga  has asked that I share my concerns with this interest list.

RFC 2831 specifies confidentiality protection (see section 2.4) whereby client-server
communications can be encrypted according to a format laid out in the RFC. The difficulty
arises when either DES or Triple DES ciphers are used for confidentiality protection.

However, RFC 2831 does not specify which DES mode (CBC, ECB, PCBC, CFB, OFB etc. ..),
should be used if DES is the negotiated cipher. This gap in the RFC allows for possible
interoperability issues allowing different vendors to potentiality opt for incompatible
DES modes. 

Possible solutions include ...

1. Add an extra directive in the SASL exchange to allow the SASL client and server to
negotiate a DES mode.

2. RFC 2831 is updated to specify exactly what DES mode should be used in the exchange,
therefore removing any potential DES mode mismatches between the client and server.

-Jonathan Bruce

Java Software JNDI
Sun Microsystems Inc.

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From: "Kurt D. Zeilenga" <[email-masked]>
Date: Wed, 20 Dec 2000 11:10:31 -0800

>interoperability issues allowing different vendors to potentiality opt for incompatible

At the top of page 5 of RFC 2831, the TS says:
      des  
         the Data Encryption Standard (DES) cipher [FIPS] in cipher
         block chaining (CBC) mode with a 56 bit key.
      
      3des
         the "triple DES" cipher in CBC mode with EDE with the same key
         for each E stage (aka "two keys mode") for a total key length  
         of 112 bits.

This seems to indicate that CBC mode is to be used.  Is this
not specific enough?

Are there other areas you believe need clarification?

>Possible solutions include ...

Approach 2, clarifying the specification such that interpretations
differences are narrowed to one, should be favored approach.