[47954] in Cypherpunks
Re: Why is blowfish so slow? Other fast algorithms?
daemon@ATHENA.MIT.EDU (Perry E. Metzger)
Thu Jan 25 01:46:58 1996
To: "James A. Donald" <jamesd@echeque.com>
Cc: daw@beijing.cs.berkeley.edu (David A Wagner), cypherpunks@toad.com
In-Reply-To: Your message of "Wed, 24 Jan 1996 22:26:12 PST."
<199601250629.WAA16623@mailx.best.com>
Reply-To: perry@piermont.com
Date: Thu, 25 Jan 1996 01:38:06 -0500
From: "Perry E. Metzger" <perry@piermont.com>
"James A. Donald" writes:
> At 07:32 PM 1/23/96 -0500, David A Wagner wrote:
>
> >If you want authentication, you must use a crypto-strength MAC.
> >Encryption (be it RC4, DES, etc.) is not enough.
>
> Not so: If the message is encrypted and checksummed with a simple
> not non cryptographic checksum, this gives you everything a MAC
> gives you, plus the message is secret.
Not so. There are unfortunate tricks that can be played here because
some encryptions preserve properties of the underlying text (like
parity) and some checksums can be manipulated because of the same.
I've asked the crypto types for information on simplified faster MACs
for use in authentication protocols for IPSEC and I have yet to get a
straight answer, so for the moment I'm erring on the side of caution, too.
Perry
