Brussels / 31 January & 1 February 2015


Thou shalt not leak your keys

Practical key privilege separation using Caml Crush

The Heartbleed vulnerability made one thing very clear, current TLS stacks lack an efficient way to isolate the cryptographic material from the application layer. Hence, this vulnerability required the massive renewal of private keys and certificates. This sure was a costly and painful process for IT departments. The most efficient approach consists of using Hardware Security Modules or smartcards to store the cryptographic material. Keys remain confidential while being usable through an API to perform cryptographic operations. PKCS#11 is a standardized security API that is widely adopted by device vendors. However, deployment of such hardware can be costly and inconvenient in many scenarios. We propose using Caml Crush, a PKCS#11 filtering proxy, in combination with software PKCS#11 tokens. This architecture leverages process isolation between the TLS stack and the cryptographic material. This low-cost alternative is immediately applicable to PKCS#11 compliant software. We demonstrate that this architecture has a low performance overhead by benchmarking the impact on web hosting scenarios.


Thomas Calderon