void silc_hmac_final(SilcHmac hmac, unsigned char *return_hash,
                         SilcUInt32 *return_len);

    This function is used to produce the final MAC from the data
    that has been added to the HMAC context by calling the
    silc_hmac_update function.  The MAC is copied in to the
    `return_hash' pointer which must be at least the size that
    the silc_hmac_len returns.  The length of the MAC is still
    returned into `return_len'.