Subject: [apps-discuss] Security hash algorithms and MTIs

From: Dave Cridland <[email-masked]>
Date: Tue, 17 Aug 2010 23:54:14 +0100

Over in the XSF, there's some talk (mostly, I admit, by me) about  
unifying the MTI recommendations we make concerning hash algorithms  
into a single specification.

I've similarly muttered in various places about unifying MTI  
recommendations for SASL, too, and I note that something similar  
applies to TLS cipher suites.

Currently, each application protocol defines an MTI authentication  
mechanism, which is mandated (by IAB fiat, I presume) to have certain  
characteristics. Similarly, application protocol designers are  
expected to know what a sensible range of TLS cipher suites to  
mandate is, this week.

Even HTTP-based protocols need to go through the entire song and  
dance, too, rather than delegating to HTTP.

Inevitably, we're a bit out of date on these things, being in, to  
paraphrase, the nose-bleed section. On the other hand, we tend to  
have definite ideas about what's most likely to be realistically  
deployable.

Sadly, though, these things change - with the result that the  
protocols specify our best compromises, frozen at a point in time.  
Worse, different protocols mandate different combinations, making  
multiprotocol clients (such as email clients) more complicated than  
it needs to be.

So, is there any interest in putting together a specification (or  
more likely set of them) which provides MTI recommendations for  
specific use-cases, such that a protocol spec can say "MUST implement  
TLS ciphers from BCP XYZ §4.2, MUST implement SASL mechanisms as  
described in §3.2", and "The hash used for this calculation is the  
current recommended signature hash from BCP XYZ"?

Dave.
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