nonPFS

NonPFS, short for non-forward secrecy, refers to cryptographic configurations or cipher suites in protocols such as TLS that do not provide forward secrecy. In practice, this means the session keys securing a connection can be derived from long-term keys rather than from ephemeral, per-session keys. As a result, if the server’s private key is compromised, past communications protected by nonPFS can potentially be decrypted.

Concretely, nonPFS occurs when a handshake uses static key exchange, such as RSA key exchange, instead of ephemeral Diffie–Hellman or elliptic-curve Diffie–Hellman (DHE or ECDHE). With static key exchange, the server’s private key is involved in deriving the session key, creating a direct linkage between long-term credentials and all past sessions. In contrast, forward secrecy ensures that session keys are generated anew for each connection, so a server key compromise does not reveal previously captured traffic.

NonPFS is commonly associated with older TLS configurations and cipher suites, for example TLS_RSA_WITH_AES_128_GCM_SHA256 or similar RSA-based handshakes. Modern standards increasingly favor forward secrecy, and TLS 1.3 requires ephemeral key exchange, effectively eliminating nonPFS in practice for newer connections.

Mitigation and best practices include disabling non-PFS ciphers, enabling PFS-capable suites (such as ECDHE_RSA, ECDHE_ECDSA, or DHE_RSA), and preferring TLS 1.2 with strong ephemeral ciphers or TLS 1.3. Regular security audits of cipher suites and configuration help reduce exposure to nonPFS and improve long-term data confidentiality.