The Design and Implementation of Protocol-Based Hidden Key Recovery

Authors: E. Goh, D. Boneh, P. Golle and B. Pinkas

We show how to add key recovery to existing security protocols such as SSL/TLS and SSH without changing the protocol. Our key recovery designs possess the following novel features: (1) The Key recovery channels are "unfilterable" --- the key recovery channels cannot be removed without also breaking correct operation of the protocol. (2) Protocol implementations containing our key recovery designs can inter-operate with standard (uncompromised) protocol implementations --- the network traffic produced is indistinguishable from that produced by legitimate protocol implementations. (3) Keys are recovered in real time, hence most or all application data is recovered. (4) The key recovery channels exploit protocol features, rather than covert channels in encryption or signature algorithms.

Using these designs, we present practical key recovery attacks on the SSL/TLS and SSH2 protocols. We implemented the attack on SSL/TLS using the OpenSSL library, a web browser, and a network sniffer. These tools allow us to eavesdrop on SSL/TLS connections from the browser to any server.