from Crypto.PublicKey import RSA

from Crypto.Hash import SHA256

from random import SystemRandom

# Signing authority (SA) key

priv = RSA.generate(3072)

pub = priv.publickey()

## Protocol: Blind signature ##

# must be guaranteed to be chosen uniformly at random

r = SystemRandom().randrange(pub.n >> 10, pub.n)

msg = 'OStoLFQC'# large message (larger than the modulus)

msg = str.encode(msg)

# hash message so that messages of arbitrary length can be signed

hash = SHA256.new()

hash.update(msg)

msgDigest = hash.digest()

# user computes

msg_blinded = pub.blind(msgDigest, r)

# SA computes

msg_blinded_signature = priv.sign(msg_blinded, 0)

# user computes

msg_signature = pub.unblind(msg_blinded_signature[0], r)

print('----msg_signature---------')

print(msg_signature)

# Someone verifies

hash = SHA256.new()

hash.update(msg)

msgDigest = hash.digest()

print('------msgDigest---------')

print(msgDigest)

print("Message is authentic: " + str(pub.verify(msgDigest, (msg_signature,))))