Subject: Re: ssh - are you nuts?!?
To: Simon J. Gerraty <>
From: Greg Hudson <ghudson@MIT.EDU>
List: tech-security
Date: 12/18/2000 03:10:20
> Authentication is pointless without a means of ensuring the
> integrity of the channel and encryption gives you that as a side
> effect.

For the record, this is a very dangerous assumption.  With some
encryption mechanisms--particularly ciphers which XOR the plain text
with a cryptographic pseudo-random byte stream--you can easily alter
the stream without the receiver noticing.  (For instance, if I know
you're sending "ok" and I want to change it to "no", all I have to do
is XOR in "\1\4".)

However, SSL provides integrity protection as well as encryption, so
in this instance your argument is unaffected by your conclusion.  (As
I understand it, SSH1 provides somewhat weak integrity protection, but
it's still prohibitively difficult to alter the stream in practice.)