What Is Forward Secrecy in VPNs? Why Is It Important?

3 min

Forward secrecy is a feature in cryptography that is rarely discussed by VPN providers and users. Since it’s influenced by the VPN protocol being used by a VPN client and a user doesn’t have control over it, it’s often not brought up for discussion. Not to mention it can get slightly technical as you try to understand the concept.

Nonetheless, we think it’s important for TuxlerVPN users to know VPN concepts that indirectly help them keep their identity, data, and devices safe and protected.

Here’s a quick rundown of forwarding secrecy and its importance in VPNs.

What is Perfect Forward Secrecy (PFS)?

Perfect forward secrecy, or forward secrecy for short, is a data security feature that protects web traffic from intrusion and surveillance. PFS ensures that even if an attacker manages to hack into an exchange between two sides (say, you and a website), they won’t be able to gain access to past data that was exchanged. Each session is protected by a unique session key.

To understand forward secrecy better, let’s take a look at symmetric encryption. In it, the data being sent is first encrypted using a public key. This protects it from interception during transit. At the receiving end, the receiver uses its private key to access the data. Every session that follows this initial handshake is further protected by session keys generated by both sides. 

However, this is problematic. An attacker can gain access to the data by hacking into the network and stealing the private key or more. That way they can gain access to all past data that was exchanged as well as set up a system to survey future exchanges. This can put your identity, data, and devices at serious risk. Perfect forward secrecy exists as a way to thwart such attempts.

It is critical to note that PFS doesn’t secure future data if an attacker manages to get both private and public keys of an exchange.

How Does Perfect Forward Secrecy Work?

Unlike general session keys used for data exchange, in perfect forward secrecy, each session is protected by an additional key. This is carried out using the Diffie-Hellman key exchange. In short, the DH key exchange depends on a shared secret as well as an individual secret. The exchange happens when both secrets are mixed, leaving any attacker with very little information.

The biggest advantage of having PFS is that it protects past communication. As every session is encrypted using unique keys, an attacker (even if they manage to hack into the exchange) can only gain access to the data shared in the current session. If they want to access past exchanges, they have to redo the brute force calculation that helped them gain access the first time.

This is where forward secrecy gets its name as the exchange moves forward without compromising the past sessions.

Perfect Forward Secrecy in VPNs

In virtual private networks, forward secrecy is a part of encryption. When you switch on a VPN on any device, all your web traffic (before it leaves your device) is encrypted as governed by the selected VPN protocol. If this protocol employs PFS as part of the key exchange – along with the encryption – your traffic data is protected by unique session keys. 

As of October 2022, PFS is an integral part of OpenVPN, WireGuard, and IPSec VPN protocols. That gives us one more reason to stress why you should stick to OpenVPN or WireGuard for maximum security online.

Generation of session keys takes time, which adds to the higher latency that VPNs are so infamous for. However, the trade-off between speed and security is worthwhile in this context.

The takeaway from this explainer is that you should always choose OpenVPN or a similarly safe protocol in your VPN. Anything less is not worth the risk.

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