Re: libssh-0.4.1 breaks application

[Aris Adamantiadis <aris@xxxxxxxxxxxx>]

Eugene,

Now I get what you mean. Indeed, it seems we have a problem, by memory
the server uses the same function than the client for the selection of
the best matching algorithm, which obviously can't be right.

I'll correct this. We have bug-material for the next release ...

Aris


Eugene Starozhilov a écrit :
> Hi Aris,
> 
> When I wrote "Now client and server choose different
> encryption algorithms during key negotiation" I meant that
> server chose aes256-ctr and client chose aes128-cbc so
> client and server just can't communicate.
> 
> According to RFC 4253:
> 
> A name-list of acceptable symmetric encryption algorithms (also
>          known as ciphers) in order of preference.  The chosen
>          encryption algorithm to each direction MUST be the first
>          algorithm on the client's name-list that is also on the
>          server's name-list.  If there is no such algorithm, both sides
>          MUST disconnect.
> 
> 
> It seems that server side (libssh-0.4.1) doesn't follow RFC 4253 in
> choosing encryption algorithm.
> 
> Regards,
> Eugene
> 
> 
> 
> --- On *Tue, 3/2/10, Aris Adamantiadis /<aris@xxxxxxxxxxxx>/* wrote:
> 
> 
>     From: Aris Adamantiadis <aris@xxxxxxxxxxxx>
>     Subject: Re: libssh-0.4.1 breaks application
>     To: libssh@xxxxxxxxxx
>     Date: Tuesday, March 2, 2010, 3:20 AM
> 
>     Hi Eugene,
> 
>     This is due to two fixes issued in 0.4.1:
>     -introduction of aes128-ctr, aes192-ctr and aes256-ctr
>     -Change in client key selector which gives the client priority on the
>     algorithms to choose.
> 
>     I'd say it's a feature and not a bug. aes256-cbc is left for
>     compatibility but by default, aes256-ctr is choosen. The latter is more
>     secure and fix a cryptographic bug in the cbc version.
> 
>     Do these changes really impact the performances or usability of your
>     application ? In last resort, you can set the preferred keys using
>     ssh_set_options().
> 
>     Aris
> 
>     Eugene Starozhilov a écrit :
>     > Hi,
>     >
>     > I just moved my application which uses sever libssh API from
>     > libssh-0.4.0 to libssh-0.4.1. Now client and server choose different
>     > encryption algorithms during key negotiation. This problem can be
>     > reproduced using samplesshd as server and ssh as a client.
>     >
>     > CLIENT (ssh)
>     >
>     > debug2: mac_init: found hmac-sha1
>     >
>     > debug1: kex: server->client aes128-cbc hmac-sha1 none
>     >
>     > debug2: mac_init: found hmac-sha1
>     >
>     > debug1: kex: client->server aes128-cbc hmac-sha1 none
>     >
>     > SERVER (samplesshd)
>     >
>     > [3] Type 20
>     >
>     > [3] Set output algorithm aes256-ctr
>     >
>     > [3] Set input algorithm aes256-ctr
>     >
>     >
>     > Any suggestions how to fix the problem will be greatly appreciated.
>     > Thanks,
>     > Eugene
>     >
>     >
> 
> 
>