Re: Security Area Response to Hash Function "Breaks"

[Magnus Nyström <magnus@xxxxxxxxxxxxxxx>]

Please see below.

In light of recent cryptanalytic results on hash functions, each IETF 
working group is asked to provide an analysis of its use of hash 
functions.

SACRED rely on DIGEST-MD5, but IMO SACRED does not become vulnerable to 
attacks due to recent results on MD5. The reasons are that in Digest-MD5, 
hashes are either done on nonces provided both by the client and the 
server or on the username and password selected by the client. Hence an 
attacker cannot perform a collision attack - in the former because the 
nonces are not known in advance and in the latter case since it would be 
equivalent to finding the password, at which point he could impersonate 
the user anyway.

Comments, anyone?

-- Magnus

On Thu, 24 Nov 2005, Russ Housley wrote:

> Below is a summary of the discussion that occurred at the SAAG session during 
> IETF 64. When MD5 or SHA-1 is used to support digital signatures or used by 
> itself, recent cryptographic research findings indicate the need for a 
> transition.  Therefore, I encourage all IETF WGs to follow the lead of the 
> Security Area in transition away from MD5 and SHA-1 toward SHA-256.
>
> TCP-MD5 is one example where a transition is needed.  In this case, a 
> transition to HMAC-SHA-1 or HMAC-SHA-256 seems like a reasonable move.
>
> Russ Housley
> Security Area Director
>
> = = = = = = = = = =
>
> During IETF 64, the Security Area Advisors Group (SAAG) session was dedicated 
> to the discussion of hash function "breaks" and the appropriate IETF response 
> to this situation.
>
> Eric Rescorla from gave a presentation on deploying a new hash function.  The 
> presentation is based on a paper that Eric co-authored with Steve Bellovin. 
> All of the IETF security protocols that were analyzed required work in order 
> to support transition to new hash functions.  The paper is available at 
> http://www.cs.columbia.edu/~smb/papers/new-hash.pdf
>
> Russ Housley gave a presentation on the Security Area response to these hash 
> function "breaks."  We should "walk, not run."  This is not a problem yet, 
> but as the attacks are improved it will become a problem.  Russ shared his 
> conclusions from the NIST Hash Workshop held on October 31st and November 
> 1st.
>  * SHA-1 should be reach its "end of life" digital
>    signatures by 2010;
>  * The IETF cannot expect any new standard hash functions
>    before 2010;
>  * The security ADs have decided that we need to transition
>    to SHA-256 now; and
>  * There will probably be another transition once a new hash
>    function is available.
>
> The IETF needs to become good at transitions as we have at least two.  Within 
> the Security Area, protocols with active WGs will be analyzed within those 
> WGs; others will be handled in SAAG.  The following directive to WG Chairs in 
> the Security Area was given:
>  * Perform Bellovin-Rescorla analysis on every protocol in
>    the WG by IETF 65; and
>  * Start standards work on transition to SHA-256, but plan
>    for future transitions.
>
> In some cases it may be appropriate to transition away from hash functions, 
> perhaps to a message authentication code.