From: futplex@pseudonym.com (Futplex)
Date: Fri, 26 Jan 1996 18:52:50 +0800
To: cypherpunks@toad.com (Cypherpunks Mailing List)
Subject: Quick MACs (Re: Why is blowfish so slow? Other fast algorithms?)
In-Reply-To: <199601260940.BAA26380@ix7.ix.netcom.com>
Message-ID: <199601261012.FAA14755@thor.cs.umass.edu>
MIME-Version: 1.0
Content-Type: text/plain


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Bill Stewart writes:
> Are there any simple but crypto-strong hash functions?
[...]
> I was thinking about using RC4 in some feedback mode as a MAC,
> but it sounds like that's not secure enough?  Is there anything
> else that's short?  MD5 requires too much code.

Phil Rogaway gave a great talk at RSADSC about keyed hashing MACs. In all he
described 12 different MACs (some of them variations on a theme), and gave
some efficiency/security tradeoff numbers relative to the security of the
underlying hash function. 

Apparently he had a paper in Crypto `95 about
bucket hashing, which is generally fast and simple and apparently pretty
secure. The idea is to place each word of the message into a unique fixed-size
subset of a large set of buckets, XOR each bucket internally, then concatenate
the results. I haven't yet read the paper (though I expect to do so soon), so
I don't know all the details. I think the notion is that you can plug in any 
pseudo-random function to select the buckets, and get provably good security 
if you know your function is suitably pseudo-random.

Check:

http://wwwcsif.cs.ucdavis.edu/~rogaway/talks/list.html

which has a link to his slides from last week, and

http://wwwcsif.cs.ucdavis.edu/~rogaway/papers/list.html

which has links to a heap of papers, including the full version of the
Crypto `95 bucket hashing one.

Futplex <futplex@pseudonym.com>
"a heap of PS papers that I _can_ print out without destroying whole forests"

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