http://i2p-projekt.i2p/spec/proposals/151-ecdsa-blinding
Use SHA-256 as follows: H(p, d) := SHA-256(p || d) HKDF(salt, ikm, info, n) A cryptographic key derivation function which takes some input key material ikm (which
should have good entropy but is not required to be a uniformly random string), a salt
of length 32 bytes, and a context-specific 'info' value, and produces an output
of n bytes suitable for use as key material.