The iMessage PQ3 protocol is an end-to-end encrypted messaging protocol designed for exchanging data in long-lived sessions between two devices. It aims to provide classical and post-quantum confidentiality for forward secrecy and post-compromise secrecy, as well as classical authentication. Its initial authenticated key exchange is constructed from digital signatures plus elliptic curve Diffie–Hellman and post-quantum key exchanges; to derive per-message keys on an ongoing basis, it employs an adaptation of the Signal double ratchet that includes a post-quantum key encapsulation mechanism. This paper presents the cryptographic details of the PQ3 protocol and gives a reductionist security analysis by adapting the multi-stage key exchange security analysis of Signal by Cohn-Gordon et al. (J. Cryptology, 2020). The analysis shows that PQ3 provides confidentiality with forward secrecy and post-compromise security against both classical and quantum adversaries, in both the initial key exchange as well as the continuous rekeying phase of the protocol.

Recently I came across a puzzling fact: the International Criminal Court hashes electronic evidence with MD5, even though MD5 is badly broken. So, why are lawyers using broken, outdated technology? The answer involves the common law system, cultural isolation, and a single man named Don L. Lewis.

Sometimes, making particular security design decisions can have unexpected consequences. For security-critical software, such as password managers, this can easily lead to catastrophic failure: In this blog post, we show how Bitwarden’s Windows Hello implementation allowed us to remotely steal all credentials from the vault without knowing the password or requiring biometric authentication. When we discovered this during a penetration test it was so unexpected for us that we agreed with our client to publish a blog post about it and tell the story.