On Thu, Dec 22, 2016 at 8:28 AM, Jason A. Donenfeld <Jason@xxxxxxxxx> wrote: > Hi all, > > I don't know what your design requirements are for this. It looks like > you're generating some kind of crypto digest of a program, and you > need to avoid collisions. If you'd like to go with a PRF (keyed hash > function) that uses some kernel secret key, then I'd strongly suggest > using Keyed-Blake2. Alternatively, if you need for userspace to be > able to calculate the same hash, and don't want to use some kernel > secret, then I'd still suggest using Blake2, which will be fast and > secure. > > If you can wait until January, I'll work on a commit adding the > primitive to the tree. I've already written it and I just need to get > things cleaned up. > >> Blake2 is both less stable (didn't they slightly change it recently?) > > No, Blake2 is very stable. It's also extremely secure and has been > extensively studied. Not to mention it's faster than SHA2. And if you > want to use it as a PRF, it's obvious better suited and faster to use > Blake2's keyed PRF mode than HMAC-SHA2. > > If you don't care about performance, and you don't want to use a PRF, > then just use SHA2-256. If you're particularly concerned about certain > types of attacks, you could go with SHA2-512 truncated to 256 bytes, > but somehow I doubt you need this. I don't think this cares about performance. (Well, it cares about performance, but the verifier will likely dominiate the cost by such a large margin that the hash algo doesn't matter.) And staying FIPS-compliant-ish is worth a little bit, so I'd advocate for something in the SHA2 family. > If userspace hasn't landed, can we get away with changing this code > after 4.10? Or should we just fix it before 4.10? Or should we revert > it before 4.10? Development-policy-things like this I have zero clue > about, so I heed to your guidance. I think it should be fixed or reverted before 4.10. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
