Why does SSH prompt for 2 passwords?

[Olivier Dony]

On Fri, Apr 18, 2003 at 03:02:23PM +0200, Willie Viljoen wrote:
> On Friday 18 April 2003 0:48, someone, possibly Joe Lewis, typed:
> 
> > Password:
> > Response:
> > joe at 192.168.1.1's password:
> 
> The first prompt is PAM challenge response authentication. This uses the PAM 
> system instead of a just a flat read of /etc/master.passwd to authenticate, 
> and is also more secure than standard plaintext authentication.
> 
> Unless your sshd is misconfigured, your configuration files and binaries are 
> out of sync (this happend when a system is upgraded without doing 
> mergemaster), this should not be happening, and you should be able to log 
> in at the first prompt. It might also be that the ssh client you are using 
> does not handle challenge response authentication properly.

Indeed and one thing you should check is whether you are not using SSH v1 by
mistake. This might happen if you are using it with arg -1 e.g :

  $ ssh -1 somehost.domain.tld
  Password:
  Response: 
  $ ssh -2 somehost.domain.tld
  Password:
  
or if your ssh client is setup to try SSH v1 first, eg if using FreeBSD's 
one as it seem, that would be :

  Protocol 1,2

in the relevant part of your /etc/ssh/ssh_config, see ssh_config(5) for more
details.

> If you are happy with standard plaintext configuration, you may edit 
> /etc/ssh/sshd_config and change the setting to this:
> 
> # Change to no to disable PAM authentication
> ChallengeResponseAuthentication no

This will do if you control the ssh server you are connecting to, but that
will only be a workaround and you probably want to fix the client problem,
as the same could happen on other hosts.

> I'd recommend you rather get PAM fixed though, or use public key 
> authentication instead, that's much more secure than any form of password 
> authentication.

I'd second on using public key authentication, as this will make remote 
logins even faster, and more secure, provided that your private key is 
properly secured. The ssh(1) man page explains it somewhat in the SSH protocol
version 2 section.

Hope this helps.

Olivier