def crypto_sign(msg, sk):
    """Return signature+message given message and secret key.
    The signature is the first SIGNATUREBYTES bytes of the return value.
    A copy of msg is in the remainder."""
    if len(sk) != SECRETKEYBYTES:
        raise ValueError("Bad signing key length %d" % len(sk))
    vkbytes = sk[PUBLICKEYBYTES:]
    skbytes = sk[:PUBLICKEYBYTES]
    sig = djbec.signature(msg, skbytes, vkbytes)
    return sig + msg