On Fri, Apr 11, 2008 at 04:30:47PM +0200, COMINT wrote: > Quick system scenario: > > You have packet [A]. > > It gets encrypted using an AES algo in a particular mode and we are > left with [zA]. > > More data [B] is added to that encrypted packet. > > Now I have [zA]+[B] in one packet and I re-encrypt it with the same > algo/key/mode. > > Have I just compromised the security somehow? I wasn't aware of > anything but something about this double encryption made something > ring in my mind so I wanted to double check...
This would certainly cause problems in if "particular mode" == OFB or counter, since (if you also reuse the IVs), you could have E(zA) == A. If you use a different (independent, unrelated) key/IV, then the existence of a weakness in this scheme would seem to provide evidence of an attack on AES, regardless of mode choice. -Jack --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]