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That statement is ambiguous, so I'll list a couple of limitation of block ciphers and cryptography in general: A raw blockcipher by itself only permutes a fixed size block (128 bits for AES). You need to add a mode of operation (together with IVs and possibly padding) to make it flexible enough for practical use. There are many modes to choose from, ...


2

The way i see it, given no context, is that indeed a block cipher is deterministic, i.e. the same message will always be mapped to the same ciphertext. Therefore block ciphers itself are semantically insecure, as ciphertext indistinguishability isn't met. You might want to check http://en.wikipedia.org/wiki/Ciphertext_indistinguishability for further ...


1

Will this method deliver true non-malleability? No. If we set the ciphertext to the value $(B, B)$, then the decrypted plaintext will have the second block as $B$ (assuming that the PCBC mode uses an implicit plaintext/ciphertext IV of 0; if it's two known constants, it's easy to adjust for that). Even if we ignore this, it also fails to make sure ...


1

Anubis (128-bit block) and Khazad (64-bit block) work by using involutional components in sequence. The complete ciphers are not fully involutional, as the key schedules and round constants prevent that from occurring. Decryption requires a different key schedule, but all other operations remain the same. They are SP-network ciphers, which are generally not ...


1

There's a lot of ways to attack this. The first thing to notice is that if you know the value of plaintext at index $i$, you can then deduce the value of all the plaintext bytes at index $i+8k$; for all integers $i$ (!). That's because the relation between plaintext and ciphertext bytes is $P_{i} = C_{i} \oplus P_{i-8}$; if you know $P_{i-8}$ (and, of ...



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