nanog mailing list archives

Re: telnet vs ssh on Core equipment , looking for reasons why ?


From: <alex () yuriev com>
Date: Tue, 31 Jul 2001 11:14:30 -0400 (EDT)


Pardon for blowing your bubble but sniffing ssh keyexchange does not do you
any good. The symmetric key is exchanged via a channel aready secured. The
keys that is used to secure the channel used to exchange the symmetric key
are exchanged via DH-based protocol. If you want to spend your time
factoring primes for next 500 years to extract the key, you are more than
welcome to try. It is crypto-101.

If you can arp spoof as indicated in the message you are replying to, you
can perform a MTM attack which SSH offers only minimal security against
(in the form of stored host keys that users often choose to ignore or not
verify the fingerprint). Look to SRP for a MTM-less password
authentication solution.

Monkey in the Middle attack on SSH is very difficult to perform. I'm cc'ing
Matt Bishop (bishop () cs ucdavis edu) who together with yours truly wrote a
paper on this in 1997. 

Cheers,
ALex


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