[openssl-dev] Pausing TLS negotiation after client hello

[Susan Hinrichs]

Hello All,

I work with Apache Traffic Server.  Many of our users use the SNI 
callback to select the certificate that the proxy will present to the 
client.  This selection can take some time.  Rather than blocking the 
callback thread, we would like to pause the negotiation from the SNI 
callback.  After the certificate has been selected, SSL_accept can be 
called again to continue the processing.

Looking at documentation and code, I did not see a way to do this, so I 
created a small patch on 1.0.1f.  I'll say a few words about the patch 
below.

But first, is there another way to achieve this in the existing 1.0.x 
API or the proposed 1.1 API?

If not, is there broader interest in such an addition?  The users within 
the Apache Traffic Server community would like to be able to use an 
un-patched openssl library.

My patch is at 
https://issues.apache.org/jira/secure/attachment/12662757/openssl-sni.patch

It adds SSL_TLSEXT_ERR_READ_AGAIN as another return value option for the 
SNI callback.  On this return value, openssl stops the negotiation and 
marks the message to be reused.  It does not signal an error to the 
client.  The next time SSL_accept is called, the client hello message is 
processed again, and if the SNI callback returns the SSL_TLSEXT_ERR_OK, 
the negotiation will continue.

Thanks for your attention,
Susan Hinrichs