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Meta has enhanced the security and transparency of its end-to-end encrypted backup system for WhatsApp and Messenger. The improvements focus on refining the distribution and verification of encryption keys, and allow for independent audits of certain infrastructure components. The updates are based on Meta's Hardware Security Module (HSM)-based Backup Key Vault architecture, which securely stores recovery secrets in tamper-resistant hardware, ensuring that neither Meta nor cloud service providers can access users' message archives. For encrypted backups, users' devices generate a 256-bit encryption key locally, which encrypts all backup data before uploading it to cloud storage. The key remains on the device in an encrypted format, with the user's password not visible to Meta or third parties. An encrypted version of the backup key is stored in the HSM-based vault using the OPAQUE password-authenticated key exchange protocol, enhancing recovery security without revealing the password. The recent updates include an over-the-air (OTA) fleet key distribution mechanism, which avoids hardcoding trusted infrastructure keys into Messenger applications. Clients receive a “validation bundle” containing the HSM fleet's public keys during runtime, with signatures verified against Cloudflare’s Key Transparency system. The vault operates across at least seven data centers using majority-consensus replication to ensure availability and integrity. Meta plans to publish cryptographic proof of each new HSM fleet deployment, allowing advanced users and researchers to verify these deployments through the open-source “mbt” (Meta Binary Transparency) CLI tool, which conducts multiple checks to confirm that fleet keys are untampered.