# Tag Info

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An alternative solution using one encryption, one cryptographic hash and one (possibly fast) non-cryptographic pseudorandom number generator operation per block. Encryption: Take the last plaintext block, and use its value (or some part of it), to seed a (possibly non-cryptographic) random number generator (note it could be XORed with the key for added ...

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Let $H(m)$ be any strong hash function. Since you want to use encryption only, we'll specify that $H(m)$ = $E_{key}(m)$ where $E$ is a 128-bit block cipher. We're trying to create an encryption mode that will cause any change to the ciphertext to propagate over all blocks of the plaintext. Strategy is to do two passes over the message, first forwards, ...

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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 ...

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FFX is not malleable. It's a strong tweakable pseudo-random permutation, where the "strong" here indicates that both encryption and decryption look like random permutations from the attacker's perspective. In particular, there's no relationship between the plaintexts of closely related ciphertexts (aside from the trivial observation that different ...

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