Google Expands Gemini 4 Carbon Access After AI Agents Verify Signal Code
Summary
Google says AI agents generated Lean proofs verifying security guarantees in its build of libsignal's compiled code. The results exclude Signal's own applications and some side channels; Google is releasing the specifications and proofs.
Key points
- Google expanded Gemini 4 Carbon access to paying developers and businesses through its API and business offering, and to Google AI Ultra subscribers.
- Google says agents running on Carbon and Claude Opus 5.5 generated about 6.5 million lines of Lean proofs for libsignal, with Lean rejecting invalid proofs.
- The proved guarantees include forward secrecy, post-compromise security and authentication, and apply to Google's build of the code's compiled machine code.
- The results do not cover Signal's own applications, and parts of the analysis excluded side channels.
- Researchers reinserted two previously patched libsignal bugs and proved that builds containing them failed the security guarantees.
- Google says its Cloud Vulnerability Research team used Carbon to confirm that two bugs in an open-source project were exploitable and help maintainers classify one as critical and patch it.
Article Details
- Event Type
- Google expanded access to Gemini 4 Carbon and reported AI-assisted formal verification of the libsignal implementation.
- Impact
- Google says Carbon for cyber helped Wiz find zero-days at two unnamed SaaS providers and helped Google’s Cloud Vulnerability Research team confirm two bugs in an open-source project were exploitable. Google DeepMind’s work used Carbon-based agents to generate roughly 6.5 million Lean proofs for Google’s build of libsignal, covering guarantees including forward secrecy, post-compromise security, and authentication. The results do not cover Signal’s own applications, and side channels were excluded from parts of the analysis.
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AlphaProof CodeSeparately, Google DeepMind introduced AlphaProof Code, which pairs human experts with AI agents to formally verify software, mathematically demonstrating that it meets defined requirements.Carbon for cyberThey still need Fairwind membership for Carbon for cyber, which Google says tops key benchmarks for discovering, exploiting and fixing vulnerabilities.Claude Opus 5.5Humans worked with agents running on Carbon and Claude Opus 5.5 to write the specifications defining what had to be proven.Gemini 4 CarbonGoogle on Tuesday expanded access to Gemini 4 Carbon and said agents built on the model helped formally verify core security guarantees in the code behind the Signal protocol.libsignalThe team applied it to libsignal, the Signal protocol’s reference implementation.