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seen Dec 28 '12 at 20:28

Dec
28
comment Can a nested block cipher avoid the meet in the middle attack by using a secret initialization vector for the inner encryption?
Thank you for very informative answer. I found the abstract of Biham link.springer.com/chapter/10.1007%2FBFb0000441. It's not yet obvious to me that it is always safer to stick with the standard modes. It might depend on the kinds of attack that are possible. In some applications chosen cipher attack is not possible. So is it possible that in those cases double DES with "inner chaining" could be stronger than TDEA with 2 keys which has its own theoretical weaknesses (seems accepted that it is not equivalent to 112 bit key)? I'm also wondering about double encryption in CTR mode..
Dec
27
comment Can a nested block cipher avoid the meet in the middle attack by using a secret initialization vector for the inner encryption?
After further thought inspired by @Thomas, the IV can be "public" in the sense of not being encrypted under the first encryption, but encrypted only with key2 during the second encryption. This second encryption would mean that the pt (in the sense of the actual input to the block cipher) for encryption 1 was unknown to the attacker and the brute force attack on encryption 1 would have to encrypt under every possible key1 using a candidate IV decrypted using every possible key2.That seems to defeat the attack.