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2

I would like to understand the algebra behind GCM's security. Well, you wrote out the mechanics of how the authentication piece of GCM works; however to understand why those mechanics work, it'd be helpful to approach it in a different way. GCM uses arithmetic in $GF(2^{128})$; this is a field; the important point is that, in a field, any nonzero polynomial ...


5

Typically when there's a variant of an ARX algorithm that goes from 32-bit words to 64-bit words, we do increase the rounds. As DannyNu mentioned, BLAKE2 is a variant of ChaCha, and while BLAKE2s (the 32-bit version) uses 10 rounds, while BLAKE2b (the 64-bit version) uses 12 rounds. One round of BLAKE2 is equivalent to two rounds of ChaCha, so we'd likely ...


0

Since most of the other answers are from before SHA-3 was standardized, I'll add another update: Keccak was chosen for SHA-3. The standard doesn't define any extendable output features for SHA-3 itself, I think because they wanted it to be a drop-in replacement for SHA-2. But it does define two closely related functions, SHAKE128 and SHAKE256, which support ...


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