Re: [TLS] TLSrenego - possibilities, suggestion for SSLv3

[Martin Rex <[e-mail]>]

Nasko Oskov wrote:
> 
> Martin Rex wrote:
> >
> > I have never used schannel myself (and haven't found programming
> > examples yet).

Nasko helpfully pointed me to Sample Code in the Microsoft PlatformSDK
(there is a WebServer and WebClient in Samples\Security\SSPI\SSL)


There is a difference between IETF GSS-API an Microsoft SSPI here.
In GSS-API, it is not possible to restart negotiation on an established
security context (handle).

As Nasko explained to me, it is possible to restart a handshake on
an existing security context handle in Microsoft SSPI (schannel SSP).
So the transfer of state from the current TLS session to the newly
renegotiated one does not require code changes above SSPI.


> 
> >
> > Nico also mentioned, that with SSPI, the renegotiation context
> > uses a different/seperate context handle that the original context.
> 
> That is not entirely true.
> 
> It is the return codes from the different APIs that tell you whether
> you should go back go negotiation or not. The application itself should
> never look at the actual packets and make decisions on their own.
>
> The way it works is that message protection/unprotection returns
> a special error code instructing the application to start handshaking
> again, using the same context.
>
> If a client wants to renegotiate, they just call the proper API with
> the current context, which emits renegotiation and handshaking begins.

Thanks for that clarification, Nasko.

I'm sorry.  I got somewhat confused by Nicos comments on SSPI.


-Martin