On Wed, 9 May 2007 15:35:44 -0400
Thor Lancelot Simon <[EMAIL PROTECTED]> wrote:

> On Wed, May 09, 2007 at 01:13:36AM -0500, Travis H. wrote:
> > On Fri, Apr 27, 2007 at 05:13:44PM -0400, Leichter, Jerry wrote:
> > > Frankly, for SSH this isn't a very plausible attack, since it's
> > > not clear how you could force chosen plaintext into an SSH
> > > session between messages.  A later paper suggested that SSL is
> > > more vulnerable: A browser plugin can insert data into an SSL
> > > protected session, so might be able to cause information to leak.
> > 
> > Hmm, what about IPSec?  Aren't most of the cipher suites used there
> > CBC mode?
> 
> ESP does not chain blocks across packets.  One could produce an ESP
> implementation that did so, but there is really no good reason for
> that, and as has been widely discussed, an implementation SHOULD use
> a PRNG to generate the IV for each packet.

Mostly right.  RFC 2405 stated:

   Implementation note:

      Common practice is to use random data for the first IV and the
      last 8 octets of encrypted data from an encryption process as the
      IV for the next encryption process; this logically extends the CBC
      across the packets.

not as a requirement but as a hint.  On the other hand, RFC 3602 says

   The IV MUST be chosen at random, and MUST be
   unpredictable.




                --Steve Bellovin, http://www.cs.columbia.edu/~smb

---------------------------------------------------------------------
The Cryptography Mailing List
Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]

Reply via email to