How Meta Is Strengthening End-to-End Encrypted Backups

Extending the Reach of Encrypted Backup Infrastructure

Meta's HSM-based Backup Key Vault underpins end-to-end encrypted backups for WhatsApp and Messenger. The system lets users protect their stored message history with a recovery code that lives in tamper-resistant hardware security modules (HSMs). Neither Meta, cloud storage providers, nor any third party can access that recovery code. The vault runs as a geographically distributed fleet across multiple datacenters, using majority-consensus replication for resilience.

The company recently introduced passkey-based encryption for backups. Now, two infrastructure changes aim to strengthen the password-based path: over-the-air key distribution for Messenger fleets, and a commitment to publishing deployment evidence.

Distributing Fleet Keys Without App Updates

Clients verify the authenticity of an HSM fleet by validating its public keys before establishing a session. In WhatsApp, those keys are hardcoded into the application. Messenger needs a different approach, since new HSM fleets must be deployed without forcing an app update. To support that, Meta built a mechanism that delivers fleet public keys over the air as part of the HSM response.

Fleet keys arrive in a validation bundle signed by Cloudflare and counter-signed by Meta. This provides independent cryptographic proof of authenticity. Cloudflare also keeps an audit log of every validation bundle it signs. The complete validation protocol is documented in the whitepaper, "Security of End-To-End Encrypted Backups."

Publishing Evidence of Secure Fleet Deployments

Transparency around HSM fleet deployment matters because it demonstrates that the system behaves as designed and that Meta cannot read users' encrypted backups. Meta will now publish evidence of the secure deployment for each new HSM fleet. New fleet deployments are rare—typically spaced years apart—but when they happen, the published evidence lets any user independently verify the deployment was done securely by following the steps in the Audit section of the whitepaper.

For the full technical details of the HSM-based Backup Key Vault, the whitepaper "Security of End-To-End Encrypted Backups" provides the complete specification.