pbkdf2_hmac_sha256.py

import hashlib
import binascii


def hmac_sha256_digest(key, msg):
    pad_key = key + b'\x00' * (64 - (len(key) % 64))
    ik = bytes([0x36 ^ b for b in pad_key])
    ok = bytes([0x5c ^ b for b in pad_key])
    return hashlib.sha256(ok + hashlib.sha256(ik+msg).digest()).digest()


def pbkdf2_hmac_sha256(password_bytes, salt, iterations):
    # hashlib.pbkdf2_hmac('sha256', password_bytes, salt, iterations)
    _u1 = hmac_sha256_digest(password_bytes, salt+b'\x00\x00\x00\x01')

    _ui = int.from_bytes(_u1, 'big')

    for _ in range(iterations - 1):
        _u1 = hmac_sha256_digest(password_bytes, _u1)
        _ui ^= int.from_bytes(_u1, 'big')

    return _ui.to_bytes(32, 'big')


password = b'secret'
salt = b'salt'
n = 1000

assert hashlib.pbkdf2_hmac('sha256', password, salt, n) == pbkdf2_hmac_sha256(password, salt, n)