3.4.3. COMPRESSED MODE
There are three kinds of information to be sent: regular
data,
sent in a byte string; compressed data, consisting of
replications or filler; and control information, sent in
a
two-byte escape sequence. If n>0 bytes (up to 127) of
regular
data are sent, these n bytes are preceded by a byte with
the
left-most bit set to 0 and the right-most 7 bits
containing the
number n.
If you think run-length-encoding compression is security, you're
even less
clued than I thought.