Deterministic signing

[celil-kj]

Does signing a messge using secp256k1_ecdsa_sign in this library require a random number generator? Are there any plans to implement RFC 6979 which describes a scheme that would make the signing process completeley determinisitc? That would make the library useful for signing messages on embedded systems where there isn't sufficient entropy such as the recently released trezor.

[sipa]

You pass the signing secret nonce in as a parameter. You can either generate it randomly (which requires a good RNG), or you can use RFC 6979 yourself to come up with it. The current API is just too low-level to say it implements or doesn't implement it - it depends on how you use it.

I do plan on implementing a slightly higher level API, where you pass in function pointers for generating randomness, and hashing. In that setting, we could have natively implemented RFC 6979.

[sipa]

This is probably a part of #4.