Reticulum/RNS/Cryptography/HKDF.py

35 lines
883 B
Python

import hashlib
from math import ceil
from RNS.Cryptography import HMAC
def hkdf(length=None, derive_from=None, salt=None, context=None):
hash_len = 32
def hmac_sha256(key, data):
return HMAC.new(key, data).digest()
if length == None or length < 1:
raise ValueError("Invalid output key length")
if derive_from == "None" or derive_from == "":
raise ValueError("Cannot derive key from empty input material")
if salt == None or len(salt) == 0:
salt = bytes([0] * hash_len)
if salt == None:
salt = b""
if context == None:
context = b""
pseudorandom_key = hmac_sha256(salt, derive_from)
block = b""
derived = b""
for i in range(ceil(length / hash_len)):
block = hmac_sha256(pseudorandom_key, block + context + bytes([i + 1]))
derived += block
return derived[:length]