credstash.py 文件源码

def _open_aes_ctr(key, nonce, ciphertext, expected_hmac, digest_method):
    data_key, hmac_key = _halve_key(key)
    hmac = _get_hmac(hmac_key, ciphertext, digest_method)
    # Check the HMAC before we decrypt to verify ciphertext integrity
    if hmac != expected_hmac:
        raise IntegrityError("Computed HMAC on %s does not match stored HMAC")

    decryptor = Cipher(
        algorithms.AES(data_key),
        modes.CTR(nonce),
        backend=default_backend()
    ).decryptor()
    return decryptor.update(ciphertext) + decryptor.finalize()