void silc_hmac_make(SilcHmac hmac, unsigned char *data,
                        SilcUInt32 data_len, unsigned char *return_hash,
                        SilcUInt32 *return_len);

    Computes a MAC from a data buffer indicated by the `data' of the
    length of `data_len'.  The returned MAC is copied into the
    `return_hash' pointer which must be at least the size of the
    value silc_hmac_len returns.  The returned length is still
    returned to `return_len'.