Use one blake2 implementation

[nazar-pc]

I noticed that Substrate uses both blake2 and blake2-rfc crates directly.

If there a specific reason for doing so or can we unify usage to one of them (presumably blake2 as it seems to be more common in general and is shared by indirect dependencies like snow) instead and remove extra dependency?

NOTE: blake2-rfc is also used in parity-db, so to remove it from dependency tree updating parity-db will be necessary as well.

UPD: blake2 doesn't support keyed hashing, so maybe blake2-rfc is the better option for now 🤷‍♂️

[davxy]

• Looks like blake2 supports keyed hashing as well
  https://docs.rs/blake2/0.10.4/blake2/struct.Blake2sMac.html
  https://docs.rs/blake2/0.10.4/blake2/struct.Blake2bMac.html
• Where is the blake2 MAC (aka keyed) used in Substrate?

[nazar-pc]

Hm, I was referring to RustCrypto/hashes#360

I'm not sure it is used in Substrate (honestly didn't check), but if one is superior in terms of feature set and comparable in performance, there is a higher chance of pulling the other dependency indirectly anyway. Still beneficial to have one dependency in Substrate, but both will be compiled in the end.

[davxy]

I've made a small recognition and looks like (as I was expecting) the keyed hash is not used within the Substrate repo:

substrate/primitives/core/src/crypto.rs

Line 135 in 23bb5a6

let hash_result = blake2_rfc::blake2b::blake2b(JUNCTION_ID_LEN, &[], data);

^ This is a blake2-256

substrate/primitives/core/src/crypto.rs

Lines 369 to 374 in 23bb5a6

	fn ss58hash(data: &[u8]) -> blake2_rfc::blake2b::Blake2bResult {
	let mut context = blake2_rfc::blake2b::Blake2b::new(64);
	context.update(PREFIX);
	context.update(data);
	context.finalize()
	}

^ This is a blake2-512

---

Parity-db is using the keyed version in one place:

https://github.com/paritytech/parity-db/blob/ab6e6bfd76e1646aa9ee54bc950c6e8b0abfbdbb/src/column.rs#L140

But I think that the interface of blake2 crate allows to get the same result... I will do a couple of experiments.