Implements the protocol from the paper SyRA: Sybil-Resilient Anonymous Signatures with Applications to Decentralized Identity
This will be used to generate pseudonym for low-entropy user attributes. The issuer will create "signature" for a unique user attribute and user uses this "signature" to create the pseudonym.
Also implements the threshold issuance of SyRA signatures
A more efficient protocol generating pseudonym and corresponding proof of knowledge is implemented in the module pseudonym_alt