Function _decode_signed_value_v2

tornado/web.py:3757–3794

(
    secret: _CookieSecretTypes,
    name: str,
    value: bytes,
    max_age_days: float,
    clock: Callable[[], float],
)

def _decode_signed_value_v2(
    secret: _CookieSecretTypes,
    name: str,
    value: bytes,
    max_age_days: float,
    clock: Callable[[], float],
) -> Optional[bytes]:
    try:
        (
            key_version,
            timestamp_bytes,
            name_field,
            value_field,
            passed_sig,
        ) = _decode_fields_v2(value)
    except ValueError:
        return None
    signed_string = value[: -len(passed_sig)]

    if isinstance(secret, dict):
        try:
            secret = secret[key_version]
        except KeyError:
            return None

    expected_sig = _create_signature_v2(secret, signed_string)
    if not hmac.compare_digest(passed_sig, expected_sig):
        return None
    if name_field != utf8(name):
        return None
    timestamp = int(timestamp_bytes)
    if timestamp < clock() - max_age_days * 86400:
        # The signature has expired.
        return None
    try:
        return base64.b64decode(value_field)
    except Exception:
        return None


def get_signature_key_version(value: Union[str, bytes]) -> Optional[int]: