Subject: Re: des-cbc cipher

From: Darren Moffat <[email-masked]>
Date: Wed, 28 Nov 2001 17:08:54 -0800 (PST)

>At 17:50 28/11/01, Bill Sommerfeld wrote:
>>On this issue, it looks like we have consensus that:
>>
>>  - there should be no mention of a des-cbc algorithm in the spec.
>>
>>  - implementations should treat algorithms they don't know about the
>>same as they treat algorithms they've been told not to use.
>
>Pardon ?
>
>I haven't seen this thread in some while.  I really disagree with the
>first conclusion.  DES-CBC is widely deployed with SSHv2 right now,
>so it ought to be mentioned.  That way a new implementer has a good 

Only the SSHv2 client and server software from SSH Inc supports DES-CBC
all other support the mandatory 3DES-CBC algorithm.  3DES != DES.

>chance of interoperating with the installed base.  Paranoid folks should 
>kindly note well that I'm not saying ANYTHING about what should be the 
>recommended or default algorithm used with SSHv2.

Since any compliant implementation MUST have 3DES-CBC they will always
interoperate providing the admin doesn't turn off 3DES.

I agree with the original statment there should be no mention of des-cbc
in the spec and implementions that don't support will correctly ignore it
if they are correctly implementing the spec.

--
Darren J Moffat

---

From: RJ Atkinson <[email-masked]>
Date: Wed, 28 Nov 2001 20:44:33 -0500

At 20:08 28/11/01, Darren Moffat wrote:
>Only the SSHv2 client and server software from SSH Inc supports 
>DES-CBC all other support the mandatory 3DES-CBC algorithm.  

Not relevant to my point in any event.  And I think that's wrong
anyway, since I know of at least one other that supports DES-CBC.

>interoperate providing the admin doesn't turn off 3DES.

Nope.  Interoperability here means able to talk DES-CBC when desired
to with another implementation that supports DES-CBC.

Note that it buys absolutely zero benefit to the user to leave DES-CBC
undocumented.  It won't make folks use 3DES, for example.  It just means
that the poor sod trying to implement a fully interoperable SSHv2 
client/server will have to try to reverse engineer the details unique
to DES-CBC.  If folks are having religion about DES-CBC, put the few
relevant details in an Appendix, mark it as purely informational or
even not recommended, but don't omit documentation that's already known
to the community...

Oh, and yes, I have commit access to an SSHv2 implementation, 
so please count these as implementer comments.

Ran
[email-masked]