def crypto_sign_open(signed, pk):
    """
    Verifies the signature of the signed message ``signed`` using the public
    key ``pk`` and returns the unsigned message.

    :param signed: bytes
    :param pk: bytes
    :rtype: bytes
    """
    message = ffi.new("unsigned char[]", len(signed))
    message_len = ffi.new("unsigned long long *")

    if lib.crypto_sign_open(
            message, message_len, signed, len(signed), pk) != 0:
        raise exc.BadSignatureError("Signature was forged or corrupt")

    return ffi.buffer(message, message_len[0])[:]
Verifies the signature of the signed message ``signed`` using the public
    key ``pk`` and returns the unsigned message.

    :param signed: bytes
    :param pk: bytes
    :rtype: bytes