AES-256
A symmetric encryption cipher with a 256-bit key, standard in OpenVPN and IKEv2 configurations.
Glossary
Perfect forward secrecy
What is Perfect forward secrecy?
Perfect forward secrecy is deriving each session key from an ephemeral key exchange and then destroying it, so a future compromise of the long-term key cannot decrypt past recorded traffic. It defends against the realistic attack: record encrypted traffic now, obtain the key later. Without it, one key compromise retroactively exposes everything captured.
Why it matters
It defends against the realistic attack: record encrypted traffic now, obtain the key later. Without it, one key compromise retroactively exposes everything captured.
What most explanations leave out
A fresh key per connection is not enough on its own: old RSA key-transport TLS generated one every time and had no forward secrecy at all, because the long-term private key could recover it. What provides the property is ephemeral Diffie-Hellman, where both sides discard their private halves. It is standard in modern configurations rather than a differentiator — WireGuard and correctly configured OpenVPN both have it. Its absence would be a serious finding; its presence is not a selling point.
Related terms
VPN protocol
The set of rules governing how the tunnel is established and how data is encrypted inside it.
Questions
- What is Perfect forward secrecy?
- Deriving each session key from an ephemeral key exchange and then destroying it, so a future compromise of the long-term key cannot decrypt past recorded traffic.
- Why does Perfect forward secrecy matter when choosing a VPN?
- It defends against the realistic attack: record encrypted traffic now, obtain the key later. Without it, one key compromise retroactively exposes everything captured.
- What do most explanations of Perfect forward secrecy leave out?
- A fresh key per connection is not enough on its own: old RSA key-transport TLS generated one every time and had no forward secrecy at all, because the long-term private key could recover it. What provides the property is ephemeral Diffie-Hellman, where both sides discard their private halves. It is standard in modern configurations rather than a differentiator — WireGuard and correctly configured OpenVPN both have it. Its absence would be a serious finding; its presence is not a selling point.
Terms are defined here because they appear in our scoring rubric or in provider reviews, not to fill a glossary.