Function _compute_digest_fallback

Lib/hmac.py:269–283

(key, msg, digest)

def _compute_digest_fallback(key, msg, digest):
    digest_cons = _get_digest_constructor(digest)
    if _is_shake_constructor(digest_cons):
        raise ValueError(f"unsupported hash algorithm {digest}")
    inner = digest_cons()
    outer = digest_cons()
    blocksize = getattr(inner, 'block_size', 64)
    if len(key) > blocksize:
        key = digest_cons(key).digest()
    key = key.ljust(blocksize, b'\0')
    inner.update(key.translate(trans_36))
    outer.update(key.translate(trans_5C))
    inner.update(msg)
    outer.update(inner.digest())
    return outer.digest()