AlphaProof Code is an AI-assisted framework for formally verifying complex software: it uses mathematical proofs to establish that code satisfies specified security properties. Google DeepMind researchers applied it to the implementation of Signal’s cryptographic protocol, which protects conversations in Signal and Google Messages. Unlike verification that checks only a protocol’s design, this effort traced properties through compiled code to the software running on devices, addressing vulnerabilities that can arise when implementation diverges from design. Researchers and AI models first translated security goals into Lean specifications, which human experts reviewed. AI agents then generated more than six million lines of proof code, while Lean independently checked each proof.
The team says the work is the first formal verification of a widely deployed cryptographic protocol’s implementation, and the first use of AI to verify such a protocol at this depth. The process took four weeks, compared with the years such work could historically require; agents also directed human reviewers to roughly one percent of the codebase for closer inspection. As a test, researchers inserted two previously fixed bugs into an isolated Signal codebase, and the system proved that each buggy version was insecure. The verified properties include protecting messages before and after a device is temporarily compromised. The researchers are releasing verification artifacts and argue that the approach could extend rigorous assurance to other critical software, including medical devices and power-grid systems, while requiring further research to scale.
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