static inline
    unsigned char *silc_buffer_put_tail(SilcBuffer sb,
                                          const unsigned char *data,
                                          SilcUInt32 len);

    Puts data at the tail of the buffer. Returns pointer to the copied
    data area.  Returns NULL on error.

    ---------------------------------
    | head  | data           | tail |
    ---------------------------------
                             ^
                               Puts data to the tail section.

    silc_buffer_put_tail(sb, data, data_len);