def sign(self, hash, random_k):
"""Return a signature for the provided hash, using the provided
random nonce. It is absolutely vital that random_k be an unpredictable
number in the range [1, self.public_key.point.order()-1]. If
an attacker can guess random_k, he can compute our private key from a
single signature. Also, if an attacker knows a few high-order
bits (or a few low-order bits) of random_k, he can compute our private
key from many signatures. The generation of nonces with adequate
cryptographic strength is very difficult and far beyond the scope
of this comment.
May raise RuntimeError, in which case retrying with a new
random value k is in order.
"""
G = self.public_key.generator
n = G.order()
k = random_k % n
p1 = k * G
r = p1.x()
if r == 0:
raise RuntimeError("amazingly unlucky random number r")
s = ( numbertheory.inverse_mod(k, n) * \
( hash + ( self.secret_multiplier * r ) % n ) ) % n
if s == 0:
raise RuntimeError("amazingly unlucky random number s")
return Signature(r, s)
def verifies(self, hash, signature):
"""Verify that signature is a valid signature of hash.
Return True if the signature is valid.
"""
# From X9.62 J.3.1.
G = self.generator
n = G.order()
r = signature.r
s = signature.s
if r < 1 or r > n - 1:
return False
if s < 1 or s > n - 1:
return False
c = numbertheory.inverse_mod(s, n)
u1 = ( hash * c ) % n
u2 = ( r * c ) % n
xy = u1 * G + u2 * self.point
v = xy.x() % n
return v == r
