Re: OFF-TOPIC: SSH authn over TLS?

[Alberto Garcia <agarciaillera@xxxxxxxxx>]

Hi,
Can you share that code to take a look at it?

Thanks

On Tue, Jun 30, 2020 at 11:28 AM Felipe Gasper <felipe@xxxxxxxxxxxxxxxx>
wrote:

> Hi Aris,
>
> I got a proof-of-concept up of a workflow that uses libssh to do key
> exchange and then public key authn on preexisting sockets, then drops the
> SSH session entirely, leaving the preexisting sockets up. That may be what
> we end up doing.
>
> It would be much simpler just to do:
>
> - Server sends a secret.
> - Client signs the secret, sends the signature and key.
> - Server verifies the signature on the key, and the key’s authz on the
> account.
>
> … which would seem to thwart replay attacks, but I’m not sure what else
> we’d be missing, and we’d be “on the hook” for maintaining basically our
> own custom “pseudo-SSH”, which doesn’t sound very appetizing.
>
> TLS client certs would involve setting up a CA or using a commercial one,
> both of which sound like workflow problems.
>
> Anyhow, thank you for your response!
>
> -FG
>
>
> > On Jun 30, 2020, at 2:04 PM, Aris Adamantiadis <aris@xxxxxxxxxx> wrote:
> >
> > Hi Felipe,
> >
> > In SSH, all authentication schemes are signature-based. Specifically
> user authentication is based on signing the master hash that's derived from
> key exchange (i.e. everything that was shared by peers + shared secret).
> SSH ensures that the authentication is safe because it's impossible for
> either party to replay or precompute that hash. I don't think TLS would let
> you extract or derive secrets based on the session's secret. You could
> craft an authentication protocol inspired by SSH on top of TLS but you'd
> have to ensure that the challenges are immune to replay, but in that case
> it wouldn't be simple anymore.
> >
> > TLS has built-in support for client certificates. It's not very
> straightforward but it might be the way to go if you insist on having
> public key authentication.
> >
> > Regards,
> >
> > Aris
> >
> > Le 30/06/20 à 01:50, Felipe Gasper a écrit :
> >> Hello,
> >>
> >>      I want to rig up a simple authentication based on SSH keys but
> over a preexisting TLS connection.
> >>
> >>      Since TLS already handles the encryption, would the authentication
> be as simple as verifying a decode of a string that the public key encodes?
> >>
> >>      Is there any prior art for this?
> >>
> >>      (I realize this isn’t really on-topic for this list, but I’m not
> sure where else to ask … ?)
> >>
> >>      Thank you!
> >>
> >> -Felipe Gasper
> >> Ontario, Canada
> >
>
>
>

-- 
Alberto García Illera

GPG Public Key <https://goo.gl/yshdwh>