Re: Encrypted TCP Tunneler

[Tatu Ylonen <ylo@cs.hut.fi>]

> However, I probably won't give up ETT yet, because there are some design 
> differences that would make ETT more useful in certain circumstances.  
> SSH seems to be design mainly as a secure telnet program, with TCP port 
> redirection added on, which suggests (although I'm not sure) that you 
> need to have an user account on the SSH server to connect to it.  It also 
> does not seem to do any filtering of TCP redirection requests.  Chaining 
> would not work well with SSH because of its packet overhead.

You are quite right here; some kind of account is needed on the
forwarder machine.  (It can, though, be an account without password
and a login shell that just sleeps.)  But anyway, TCP port forwarding
is not its main function.  (I don't think the packetizing is such a
major overhead though - it currently transfers around 400kbytes/sec
over ethernet encrypted with RC4 between P90 machines.)

> authentication schemes.  What are the relative advantages of your protocol
> over a more straight-forward DH + signature of exchange values?  DH would
> provide forward secrecy directly without the need to change the server key
> every hour. 

The reasons for this key exchange are mostly historical.  If I was
starting the implementation now, I would use DH + signatures.  The
performance difference is not very big, but DH + signature would be simpler.

    Tatu