Subject: Re: [TLS] Design Alternatives for Kerberos + DH

From: Rick van Rein <[email-masked]>
Date: Mon, 19 Oct 2015 10:36:27 +0200

Hello Benjamin,

> No, mutual authentication requires the client to receive a message from
> the server.

Yes, I know -- the server needs to handle the session key or the subkey
to prove posession of its KDC-stored service key.  By using it, the client
can be convinced or server identity.

> This could be implicit

I think it automatically is with TLS, since the Finished messages won't
succeed until both parties have derived the same master secret, which
if it involves the session key or subkey proves the server's identity in an
implicit manner.

I do believe a long-enough Finished message is required though.  For
the TLS_ECDHE_KRB_ CipherSuites I've proposed a verify_data_lenth
to match the required certainty from the message; if we mix Kerberos
client "certificates" info other CipherSuites like TLS_ECDHE_RSA_ then
a client SHOULD negotiate a high-enough value and the server MUST
support that.  It requires TLS 1.2 to do these things.

-Rick