The Signal Protocol is a set of cryptographic specifications that provides end-to-end encryption for private communications exchanged daily by billions of people around the world. After its publication in 2013, the Signal Protocol was adopted not only by Signal but well beyond. Technical information on the Signal Protocol can be found in the specifications section of our docs site.
Today we are happy to announce the first step in advancing quantum resistance for the Signal Protocol: an upgrade to the X3DH specification which we are calling PQXDH. With this upgrade, we are adding a layer of protection against the threat of a quantum computer being built in the future that is powerful enough to break current encryption standards.
This post is written to introduce this work to non-experts, and will review what quantum computing is and the challenges it presents for current cryptographic algorithms, before providing a high level overview of how we are adapting our specifications to answer these challenges. If you would like to skip this summary and explore our PQXDH specification in depth, you can read our technical whitepaper here.