[tor-dev] Re: Using hidden service key with TLS client authentication

[Jeremy Rand via tor-dev <tor-dev@xxxxxxxxxxxxxxxxxxxx>]

techmetx11 via tor-dev:
> Hi tor-dev mailing list,
>
> Is there a way to capsulate a Tor hidden service Ed25519 private key 
> inside a TLS EE certificate and use it in TLS?
>
> I wanted to use this specifically for XMPP's server-to-server TLS 
> connections, which uses mTLS to prove if the client connecting is who 
> they say they are. Currently with XMPP Tor server-to-server connections, 
> we have to use dialback (telling the server to connect back to the 
> client to authenticate its identity, https://xmpp.org/extensions/ 
> xep-0220.html) to prove it, which is a legacy and insecure form of 
> server-to-server authentication
>
> If this is possible, then it would get rid of a reason to keep dialback 
> around and less roundtrip for the server authentication.
>
> Kind regards,
>
> techmetx11

Hi!

Possible via PKCS#11 (basically the same logic as for TLS server certs), 
though I haven't written the TLS CCA code paths for that yet. However, 
probably not desirable in the way that you want. In some setups (e.g. 
Whonix), the application and the Tor daemon are in different trust 
domains. If you *replace* the onion dialback authentication with TLS 
CCA, then anyone who compromises the application can bypass the 
authentication. Of course, with your current scheme, anyone who 
compromises the Tor daemon can bypass the authentication. The most 
secure scheme is probably to do both TLS *and* onion auth, in both 
directions; that way an attacker would have to compromise both the 
application and the Tor daemon in order to bypass auth.

Cheers,
--
-Jeremy Rand
Lead Application Engineer at Namecoin
Mobile email: jeremyrandmobile@xxxxxxxxxx
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