Comment by kpdemetriou
2 years ago
Re: BLAKE2, I'm not sure it's fair to say that BLAKE2 is more widely used overall. But I do agree BLAKE2 is a bit of an outlier in terms of adoption. I think part of the reason is that SHA2 remains the go-to option, else I'd expect the ecosystem to consolidate around SHA3.
Re: Serpent, there are many things to unpack here but, in summary, you don't know a priori how large of a security margin you need (given the primary function of a cipher, you want to pick the conservative option), efficiency concerns become much less relevant with hardware-accelerated implementations and years of Moore's law performance uplifts, low-power devices can take advantage of much lighter algorithms than Rijndael OR Serpent, ease of implementation does not equal ease of correct/secure implementation vis-a-vis side channel attacks, and certainly if Serpent was chosen you wouldn't see Rijndael talked about much.
Blake2 also uses a very SHA2-like construction (a HAIFA construction, which is based on Merkle-Damgard). I believe this was the main reason SHA3 was chosen to be something completely different (a sponge construction). If SHA2 was found to be insecure, Blake2 would be at more risk of also being broken than Keccak.
Speculatively, if SHA2 is broken without breaking Merkle-Damgard hashes in general, Blake2/3 could well become SHA4.
> I'm not sure it's fair to say that BLAKE2 is more widely used overall
Ah, maybe my experience is biased then. I keep coming across BLAKE2 implementations, but rarely hear so much as people considering to use SHA-3 somewhere. If anyone has actual numbers on this, that would be interesting.
It would be good if SHA-3 is being used because then chip makers have a reason to bake it into their hardware, which is exactly where the biggest gain over SHA-2 is expected. If that happens, and all else being equal (no cracks appear in Keccak), I'd be surprised if BLAKE2 remains as popular!
> you don't know a priori how large of a security margin you need
True, so this can be argued to be an educated guess at first. But then confidence increases over time. It seems to be expected that, more than 20 years later, people aren't considering Serpent anymore. Is it because it wasn't chosen as AES? Certainly partially, but BLAKE2 (I'll admit it does seem like an outlier) likely will still be talked about in the future so standardization is not the only factor.
I didn't see actual benchmarks, but Serpent sounds at least three times slower than Rijndael for, by now, no tangible benefit. What would be interesting is if there were AES competitors that are also fully unbroken and are more efficient than Rijndael, or easier to implement, etc.
> I didn't see actual benchmarks, but Serpent sounds at least three times slower than Rijndael
You can read the original report on the candidates: https://nvlpubs.nist.gov/nistpubs/jres/106/3/j63nec.pdf
To save you some time, one software evaluation is on page 531. Serpent performs worse in software than Rijndael (AES) just about everywhere (note they use categories rather than precise metrics, but you can dig into that if you want). By contrast, one hardware evaluation is on page 539. Serpent has the highest throughput for the lowest "area" i.e. required. These results repeat on p541.
So it depends on whether you are comparing a software or hardware implementation.
I wish chip makers would bake the elliptic curve used in Bitcoin and Ethereum (secp256k) as well, instead of the entire industry coalescing around secp256r, which many suspect was somehow weaker (since its parameters are some weird large number X instead of a hard-to-game number like 15, leading some to believe that the first X-1 candidates were tried and X was found to be weaker).
The real reason I would have liked that to be the case is so that one could use WebAuthn and Subtle Web Crypto to sign things and have the blockchain natively verify the signature.
As it is, I am hoping that EVM will roll out a precompiled signature verifier for secp256r, which is on the roadmap — they say!
There are a few different on-chain implementations of secp256r1 signature verification for use with passkeys, my favorite of which is demoed at https://p256.alembic.tech
Work is also being done on SNARK-based cross-curve signature verification
But I fully agree, especially with the growing popularity of account abstraction, the EVM desperately needs a secp256r1 precompile!
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