patch adding none cipher/mac for ssh v2

[Michael A Stevens]

On Sat, 13 Nov 2004, Ed Avis wrote:

> Douglas E. Engert wrote:
>
>> So why do you need ssh without encryption? Won't telnet or rsh do
>> just as well?
>
> This is just a personal preference but I'd rather not use telnet or
> rsh for anything.  They are crusty.  Much better to use ssh all the
> time - only one daemon to run instead of two, only one command to run.
> Anything that helps get rid of telnet and rsh is a good thing!
>
> Those are my subjective feelings. A more rational explanation is to
> say that the ssh and sshd code is of good quality and well audited for
> security holes.  You can't be so confident about rshd or telnetd.  If
> you want a remote connection without encryption, ssh is certainly a
> more secure way to do the job than any of the old stuff.
>
> Users who ask for ssh with 'none' encryption are paying the openssh
> developers a compliment by showing that ssh is worth using for its
> code quality and ease-of-use alone, even without the added security of
> strong encryption.

I think the idea here is that it should be reasonably hard for people to 
shoot themselves in the foot by turning off encryption. If you put none 
into the supported ciphers list, then you risk it getting picked if no 
other ciphers match. A dual stage setup where a user needs to enable 
sending none, and then prompts them if that is the only one available 
would be the most appropriate. The problem with is that none almost 
defeats the purpose of ssh and it should be really hard to do this by 
accident.

If you absolutely must use none and want authentication security, then 
re-kex'ing with a changed cipher list would let you switch to none after 
authenticating. Alternatively you could use RSA keys and not use passwords 
at all. If you leave the MAC algorithm in place you should be protected 
against injection attacks, but all your session info will be in the clear, 
so if you login via password to another system, your password will be 
going in the clear over the local line.


Mike