[openssl-dev] tls_session_secret_cb method return value

[Ian McFadries (imcfadri)]

Hi Emelia,

Thanks for your response.  Your pointer to the discussion in March has answered my question.  Now that I am aware of the intended use of the return values from the secret callback, I am all set.  I have changed our code to return the appropriate values in the callback.  My only suggestion is that you may consider adding comments to the tls_session_secret_cb definition and/or declaration to document the use of the callback return value.

Thanks,
Ian

From: openssl-dev [mailto:openssl-dev-bounces at openssl.org] On Behalf Of Emilia Käsper
Sent: Tuesday, August 11, 2015 6:13 AM
To: OpenSSL development
Subject: Re: [openssl-dev] tls_session_secret_cb method return value

Hi Ian,

Thanks for the report!

Your colleague John Foley suggested to treat this error as unrecoverable:  https://mta.openssl.org/pipermail/openssl-dev/2015-March/001030.html

The error is set while processing the ServerHello, at which point the PAC has already been sent to the server in the ticket in the ClientHello, and it's the server's call whether it'll be resuming. So either
(a) we make the assumption that the server would agree that the PAC has expired and not attempt a resumption - and we make the resumption attempt an internal error; or
(b) the client-side check for expiration would have to be moved to an earlier place in the handshake.

I am afraid that you know better than me what the intended behaviour is. How about you describe the complete correct flow and propose a patch?

Cheers,
Emilia

On Mon, Aug 10, 2015 at 5:34 PM, Ian McFadries (imcfadri) <imcfadri at cisco.com<mailto:imcfadri at cisco.com>> wrote:

I am trying to determine if the tls_session_secret_cb return value is used to indicate an unrecoverable error has been encountered
(i.e. bad pointer for data needed to calculate secret) or if it is intended to be an indicator that the session secret is deemed
invalid (EAP-FAST PAC expired resulting in new session therefore determine that secret should not be calculated).

The code I am working on is using the tls_session_secret_cb return value as the latter specified above, and that resulted in our
implementation of EAP-FAST to break when a PAC expires after we picked up release 1.0.1l of OpenSSL.  A change was made in s3_clnt.c
ssl3_get_server_hello method at line 889.  Previously, if tls_session_secret_cb returned 0 no action was taken, but the change
resulted in SSLErr if tls_session_secret_cb returned 0.

I believe that we should treat the tls_session_secret_cb return value to indicate an unrecoverable error only.  Then in the scenario
where the PAC expires, although we would not calculate the secret, it will work fine since the secret will be calculated later in
OpenSSL when servicing the client key exchange.

_______________________________________________
openssl-dev mailing list
To unsubscribe: https://mta.openssl.org/mailman/listinfo/openssl-dev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mta.openssl.org/pipermail/openssl-dev/attachments/20150812/821f13e9/attachment-0001.html>