Re: Correction: Re: Serious crypto problem fixed by envelope HMAC method insteadof currently used prefix

[Steve Friedl <steve () unixwiz net>]

On Mon, Nov 20, 2006 at 01:45:45PM -0500, Omirjan Batyrbaev wrote:
> This would have been a problem if the HMAC was just SHA-1(...) or MD5 (...)
> or similar type of prefix HMAC. However, the HMAC used in TLS is more
> involved construct (see RFC 2104) and the attack is not applicable.

It is indeed more complicated than that, and though one could certainly
look at a boring RFC, it would sure be easier to look at a colorful
technical illustration that shows how HMAC works.

        An Illustrated Guide to IPSec
        http://www.unixwiz.net/techtips/iguide-ipsec.html#hmac

Steve :-)

--- 
Stephen J Friedl | Security Consultant |  UNIX Wizard  |   +1 714 544-6561
www.unixwiz.net  | Tustin, Calif. USA  | Microsoft MVP | steve () unixwiz net