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Comment by newpavlov | Hacker News Reader

>Keccak for all of symmetric crypto: it is suited both for encryption, hashing, duplex transcripts for ZK protocols etc.

Unfortunately, Keccak and sponge constructions in general are inherently sequential. Even with hardware acceleration it heavily restricts possible performance. For example, AES-CBC encryption is 4-8 times slower than AES-CTR on high-end CPUs with AES-NI available. VAES makes the difference even bigger. Algorithms like AES-GCM, ChaCha20, and BLAKE3 are designed specifically to allow parallelization.

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How much does the lack of parallelization matter in practice though? Sure, AES-CTR can be parallelized, but the authentication function you're probably pairing it with likely can't. And in a lot of cases I'm aware of where encryption parallelism is important for performance (e.g. line-rate VPN encryption), you can achieve parallelism for the operation as a whole without achieving stream based parallelism. In the VPN example, even if you can't encrypt all the blocks in a single packet in parallel, you can probably achieve just as much parallelism speedup by encrypting multiple packets in parallel.

> Unfortunately, Keccak and sponge constructions in general are inherently sequential.

Couldn't you simply using BLAKE3 instead? To my knowledge BLAKE3 exactly was designed to solve this "parallelism problem" by combining the "cryptographic ideas" of BLAKE2 with the binary tree structure of Bao (the latter was designed to make the hash construction easy to parallelize).

Fwiw I don't think there's anything inherently sequential about the Keccak permutation itself. KangarooTwelve is a fully parallelizable hash built on Keccak. (Though they did use the sponge construction on the XOF side, so that part is serial.)

I meant the absorb and squeeze part. The permutation itself (or more specifically its round) could be efficiently implemented in hardware, but you can't mask latency by parallel application of the permutation. Yes, KangarooTwelve is an improvement in this regard, but the grandparent was talking specifically about Keccak/SHA-3.

Sorry for lack of clarity, but i was saying “Keccak” and not “sha3” for that specific reason: it’s a permutation building block suitable for a whole range of constructions - cshake, kangaroo etc. sha3 specifically is an overkill and unnecessary imho.

CShake128 is much better replacement for hmac and sha512 in (zk)proofs, while Kangaroo for things like FDE and massive volumes of data.

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