def _DLEQ_derive_challenge(x, y, a1, a2):
""" Compute (common) challenge e = H(x_1, y_1, a_11, a_21, ..., x_n, y_n, a_1n, a_2n).
Compared to the SCRAPE paper the order of the arguments is changed for a consise implementation.
"""
n = len(x)
hasher = hashlib.sha512()
for i in range(n):
hasher.update(bytes(x[i]))
hasher.update(bytes(y[i]))
hasher.update(bytes(a1[i]))
hasher.update(bytes(a2[i]))
return Scalar.reduce(hasher.digest())
def deterministic_random_scalar(purpose: Optional[str] = None, counter: Optional[int] = None):
purpose = "__scalar__ || " + (purpose or "")
return Scalar.reduce(deterministic_random_bytes(64, purpose, counter))