Secp256k1 with Non-Deterministic Signatures

Question

I am using an HSM which signs bytes using the secp256k1 curve. For a given set of input bytes, I blake2b hash them and sign them.

My understanding is that most cryptocurrencies use deterministic signatures (RFC 6979) in order to prevent transaction malleability. The particular HSM I am using does not generate deterministic signatures and instead chooses a random k which results varying r and s values.

Is there any way to get this set up to generate a valid signature for Tezos? Specifically: - Does Tezos require deterministic signatures? - If yes, is it possible to generate a deterministic signature from a non-deterministicly chosen r, s, the input bytes, and the public key?

Edit:

I've been able to determine that Tezos will accept a non-deterministic signature.

However, sometimes I receive an r or an s value that is 33 bytes long. Is there a way to normalize these values to 32 bytes? It appears that Tezos will only accept two 32 byte values.

Answer 1

It shouldn't make a difference how you pick k, deterministically or not. It's random and is supposed to be kept secret by the signer, so there's no way to tell what k was used by just looking at the signature.

Tezos expects exactly 64 bytes for a secp256k1 signature https://gitlab.com/tezos/tezos/-/blob/master/src/lib_crypto/base58.ml

Per this question you might need to normalize (r, s) to lower s form (r, -s mod n) is also a valid signature and Tezos only accepts one. Invalid Signature for Tezos transaction

You are getting 32 bytes and 33 bytes value because of the weird DER encoding. Here's a description that will let you get the actual value for r and s.

https://superuser.com/questions/1023167/can-i-extract-r-and-s-from-an-ecdsa-signature-in-bit-form-and-vica-versa

https://bitcoin.stackexchange.com/questions/12554/why-the-signature-is-always-65-13232-bytes-long