Signal: Quantum Resistance and the Signal Protocol

summerheat · Sep 20, 2023

https://signal.org/blog/pqxdh/

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.

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Our new protocol is already supported in the latest versions of Signal’s client applications and is in use for chats initiated after both sides of the chat are using the latest Signal software. In the coming months (after sufficient time has passed for everyone using Signal to update), we will disable X3DH for new chats and require PQXDH for all new chats. In parallel, we will roll out software updates to upgrade existing chats to this new protocol.

Future Work
PQXDH protects messages exchanged on Signal against the threat of a future quantum computer. We will need to make further upgrades to address the threat of an attacker with a contemporaneous quantum computer. Further research in the area of post-quantum cryptography will be needed to fill in the remaining gaps. We recommend reading the security considerations section of our PQXDH whitepaper for more information on the areas of open research.
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Signal: Quantum Resistance and the Signal Protocol

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Signal: Quantum Resistance and the Signal Protocol

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