From: ljo@ausys.se (Johansson Lars)
Date: Wed, 13 Dec 1995 01:26:07 +0800
To: cypherpunks@toad.com
Subject: Blinding against Kocher's timing attacks
Message-ID: <95Dec12.160243gmt+0100.53783@void.ausys.se>
MIME-Version: 1.0
Content-Type: text/plain




Ron Rivest wrote (at sci.crypt):
>The simplest way to defeat Kocher's timing attack is to ensure that the
>cryptographic computations take an amount of time that does not depend on 
the
>data being operated on.  For example, for RSA it suffices to ensure that
>a modular multiplication always takes the same amount of time, independent 
of
>the operands.
>
>A second way to defeat Kocher's attack is to use blinding: you "blind" the
>data beforehand, perform the cryptographic computation, and then unblind
>afterwards.  For RSA, this is quite simple to do.  (The blinding and
>unblinding operations still need to take a fixed amount of time.) This 
doesn't
>give a fixed overall computation time, but the computation time is then a
>random variable that is independent of the operands.

Does anyone know whether David Chaum's patent on
blind digital signatures extends to this application?

Kind regards,
/Lars Johansson

ljo@ausys.se
http://www.ausys.se/defaulte.htm