I have unsubscribed from this mailing list. Please remove my name from your personal address lists. Thanks. ahg3 ---------- From: Patrick Horgan[SMTP:patrick@Verity.COM] Sent: Tuesday, October 24, 1995 1:08 PM To: fc Cc: cypherpunks Subject: MD5 concerns, was Re: Netscape Logic Bomb detailed by IETF
channel. I think that Netscape uses an MD5 checksum which the members of this list seem to place unlimited trust in (incorrectly in my view,
This is the second time you've implied that an MD5 checksum might not be as secure as we think. Could you share your thinking on this? I had believed from reading the algorithm that it's not possible to predict how a change in the input will affect the checksum. Given a modified version of netscape for example, how would you change some non-critical portion of the code to get the same checksum that the original should have. I suppose that give n bits of non-critical space in the code, (non-critical meaning that changing them will have no effect on the execution of the code, and assuming that you don't want to change the length of the code), that you could try all possible combinations of those bits, or 2^n trials and see if you get the correct MD5 checksum. If you do, then on average you'd actually only have to try 2^(n-1) trials. What if you don't? What would you do then? MD5 produces a 128 bit output, and it would seem likely that this would be hard. As far as I know there are no known attacks for any MDx algorithms in spite of Ron's worries about MD4. It's a subject of on-going research though, and it is only "conjectured that it is computationally infeasible to produce two messages having the same message digest, or to produce any messages having a given prespecified target message digest." (RFC 1321) So, if you have newer information, or pointers to any papers, (other than the ben Boer and Bosselaers papers), could you let me know? Thanks, Patrick _______________________________________________________________________ / These opinions are mine, and not Verity's (except by coincidence;). \ | (\ | | Patrick J. Horgan Verity Inc. \\ Have | | patrick@verity.com 1550 Plymouth Street \\ _ Sword | | Phone : (415)960-7600 Mountain View \\/ Will | | FAX : (415)960-7750 California 94303 _/\\ Travel | \___________________________________________________________\)__________ /