openssh unix dev - Apr 2013 - Auth_Banner question

Hi all,

I'm working with a pure PHP implementation of the SSH2 protocol. I've 
read the rfc and the thousands of lines in this project: 
http://phpseclib.sourceforge.net/

I'm simply trying to add a feature that will capture and display the 
USERAUTH_BANNER displayed by Open sshd prior to login.

When I connect to my opensshd server configured with the banner from 
openssh on any linux distro, I see the banner and all is well.
When I debug this PHP library, it never sees a binary packet of type 53- 
the Banner packet. I can connect, authenticate, etc, but a full
dump of the data shows no banner was sent by sshd. This makes me sad.

So, I'm wondering if there is some way to trigger sshd to send the 
banner. Can I request it explicitly with some message to sshd?
I know that according to the RFC it can be sent after authentication 
begins, but before it succeeds, but is there a specific sequence of events
in sshd where I can expect to see it?

Thanks so much!

-JP

On Fri, 19 Apr 2013, Jonathan Pauli wrote:
> I'm working with a pure PHP implementation of the SSH2 protocol.
I'm terrified.
> So, I'm wondering if there is some way to trigger sshd to send the
banner.
> Can I request it explicitly with some message to sshd?
sshd sends the banner for protocol 2 connections at before it responds to
the the first SSH_MSG_USERAUTH_REQUEST packet. I.e

Client: SSH_MSG_USERAUTH_REQUEST
Server: SSH_MSG_USERAUTH_BANNER
Server: SSH2_MSG_USERAUTH_SUCCESS, SSH2_MSG_USERAUTH_FAILURE
        (or a userauth method-specific reply)

Have a look at auth2.c:input_userauth_request() to see how it works.

There isn't anything else you can do to trigger it than attempting
authentication.

-d