6

The number of rounds does not directly influence security; it depends at least as much on the complexity of those rounds. That said, it is possible to use the percentage of rounds for which there are attacks as an indication on how much crypt-analysis has advanced (disregarding those attacks that are worse than brute force, of course). One tricky thing with ...


6

This is a slight variation of the autokey cipher, which was invented by Vigenere, and can be seen as another variant of the Vigenere cipher. The major differences are: It used a different alphabet, the keysize is fixed, and you reuse the ciphertext instead of the key or plaintext. Therefore, even without looking at the the details, it is fairly obvious that ...


3

In most cases, you should probably use AES, especially if there is hardware support. In some cases, it might make sense to use one of the others. For example, the simplicity of Threefish would make sense for an embedded controller using a micro lacking hardware support for AES. Its lack of S-Boxes reduces the amount of ROM needed. If you don't need the ...


2

Is the following build stronger than 2DES or 3DES with 2 different keys (or even normal DES)? $DES(DES(x,k),\overline{k})$ It is only slightly stronger than DES; it is considerably easier to attack than 2DES or 3DES. The most practical attack against DES is brute force; simply try the various possible keys until you stumble on the correct one. With a ...


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