encrypted telnet

[William Stephen Kish <wk0x@ANDREW.CMU.EDU>]

Hello,

I've created this simple little program that allows for encrypted
telnet sessions (between unix hosts) without any modification to the
system telnetd or telnet programs.

The system consists of a pair of programs: 1 running on the target
machine (Host B) and 1 running on the machine being telneted from
(Host A).  (These daemons require no special permissions -- they run
as normal user processes. Also, both daemons are really the same
program; each is started with a different switch to let it know which
hat to wear...)

Instead of telneting directly to Host B, the user telnets to a special
port on his own machine ("telnet HostA 10000").  This connects him to
the encryption daemon.  Upon makeing this connection, this Host A
encryption deamon opens a TCP connection to the peer encryption daemon
on Host B. This Host B deamon then opens a connection to port 23 (the
normal telnet port) on it's own machine. Thus, all data from the user
is passed to the encryption daemon on its local machine where it is
encrypted and sent over the net to the peer daemon on the target
machine. There the data is decrypted before being passed to the local
telnetd process.  Data flowing in the reverse direction undergoes a
similar process. All of this is transparent to the user and telnet
processes.

What I need now is a strong stream cypher to drop into these daemons.
Can anyone supply references to apropriate algorithms or code?  A good
cypher should be resistant to known plaintext attacks, since telnet
sessions start out with lots of known plaintext (telnet options, login
banner, motd, user id, etc...).

If there is interest, I'll look into releasing this when it's complete.

Thanks,
Bill Kish
kish+@cmu.edu