[Twisted-Python] (conch) credentials.signature always None?

[Paul Swartz]

On Wed, Jan 19, 2011 at 6:55 PM, Saúl Ibarra Corretgé <saghul at gmail.com> wrote:
> Hi all,
>
> I'm experiencing something weird while writing a simple SSH server,
> and I wonder if anyone did run into this before:
>
> On every snippet I see around regarding public key authentication, the
> signature is checked as follows:
>
> #        if not credentials.signature:
> #            return failure.Failure(ValidPublicKey())
> #        try:
> #            public_key = keys.Key.fromString(data=credentials.blob)
> #        except (keys.BadKeyError, keys.EncryptedKeyError):
> #            return failure.Failure(ConchError("Public key error"))

If it's not continuing, that's a problem with the other side.  What
happens with the SSH protocol is:

C: sends a message asking 'if this public key okay?' without sending
any signed data
S: says either "no it's not valid for this account" or "yes it is
valid, please prove you have the private key"
C: if yes, sign some data and send the signature; otherwise try a
different key or different authentication mechanism

The 'if not credentials.signature: return
failure.Failure(ValidPublicKey())' code is how the server tells the
client it's a valid key, but needs to prove it also has the public
key.

-p
-- 
Paul Swartz
paulswartz at gmail dot com
http://paulswartz.net/
AIM: z3penguin