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From Specs to Apps: Verifying and Monitoring Models of Signal and WhatsApp

Researchers use the SpecMon runtime monitor to verify WhatsApp Web and Signal Desktop against formal Signal protocol models, finding undocumented libsignal fork differences.

The paper applies SpecMon, a runtime monitoring tool, to check whether executions of WhatsApp Web and Signal Desktop conform to formal models of the Signal protocol. The authors instrument both applications and build Tamarin-compatible multiset-rewrite models, including the first model of WhatsApp Web's implementation and the most detailed model to date of Signal's original protocol. They verify authentication and secrecy properties for core Signal protocol components, show monitoring detects deliberately injected faults with low overhead, and identify previously undocumented behavioral differences between the original libsignal library and WhatsApp's fork.

arXiv cs.CR · 5d agoResearch

Signal's new security feature checks if your encrypted chats were tampered with

Signal adds automatic key verification, a key-transparency system audited by Cloudflare and Trail of Bits that detects key-directory tampering in E2EE chats.

Signal launched automatic key verification, a key-transparency system that confirms a phone number or username remains bound to a consistent encryption key across Signal's key directory. Cloudflare and Trail of Bits independently audit the system, with cryptographic protection preventing auditors from seeing users' identifiers in plaintext. The feature mitigates key substitution by a compromised directory or privileged insider, though it currently requires the contact's phone number and users can fall back to manual Safety Number verification.

Help Net Security · Aug 12, 2026Tools