Meta open sources NTS implementation and launches authenticated time service

Meta has released its NTS (RFC 8915) implementation, including the protocol, server, and client, via its Time library on GitHub. The company has also launched a public time service at nts.meta.com to provide verifiable time, addressing security vulnerabilities inherent in unauthenticated NTP. The implementation uses a stateless cookie mechanism to ensure scalability without requiring per-client state replication.

Technical details of Meta's NTS deployment

• Two-phase process: Uses TLS 1.3 over TCP/4460 for Key Establishment (NTS-KE) and standard NTPv4 over UDP/123 for authenticated time exchange.
• Stateless design: Servers do not store per-client state; instead, they use cookies containing session keys sealed with AES-SIV, derived from a shared master secret and the current day.
• AEAD support: Negotiates algorithms including AES-SIV-CMAC-256 (mandatory per RFC 8915), AES-SIV-CMAC-512, and AES-128-GCM-SIV.
• Security improvements: Protects against forged packets and replay attacks by using unique identifiers and encrypted cookies within the response authenticator.

Why it matters

By providing a verifiable time source, Meta aims to secure critical security decisions like TLS certificate validation and token expiry, which rely on accurate local clocks.