4 ms·
CBC is a way ("the" way, really) to take something like AES that works in 128-bit blocks and apply it across an arbitrarily long stream of data. Is CTR mode co
by tsuraan 16y ago
CBC is a way ("the" way, really) to take something like AES that works in 128-bit blocks and apply it across an arbitrarily long stream of data.
Is CTR mode considered insecure, or is it just not appropriate here?
- tptacek 16y agoCTR doesn't have this problem, but it has a very similar one, and the consequence of making that mistake is (unlike with CBC) completely horrible.
- tsuraan 16y agoWhat is the analogous mistake you'd make in CTR? The problem here was setting the IV to the last block of the previous stream, right? Would the analog to CTR be continuing to count in the same sequence? Also, I know this isn't the best forum for crypto discussion, but what is (especially for people who are almost totally ignorant but want to learn, like myself)?
- tptacek 16y agoThe underlying ("moral", to coin a term) flaw isn't "using the last cipherblock of the last message as the IV for the next message; it's using predictable (or, worse, repeated) IVs. An attacker who can get a target to repeat a CTR nonce can often coerce that target to repeat an entire keystream, which is devastating.
- yuhong 16y agoYep, can be made with any stream cipher.
- tedunangst 16y agoA good forum for discussion, or reading along, used to be sci.crypt with the spam filter turned up to 11+, but I haven't checked it out recently. Or http://marc.info/?l=cryptography&r=1&b=201010&w=2 http://marc.info/?l=cryptography&r=1&b=201010&w=...