Perfect Forward Secrecy: The Pillar of Internet Security

Find out what perfect forward secrecy is, how it can help you stay safe online, and why it is regarded as the foundation of internet security.

Bojan Jovanovic Image

October 17,2022

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Chances are you’ve heard of the term “internet security” before but may not be sure what it entails exactly. In short, internet security refers to measures taken to protect electronic information from being accessed by unauthorized individuals.

An essential component of internet security is perfect forward secrecy. This article will help you learn what perfect forward secrecy is and how it works.

What Is Perfect Forward Secrecy? 

Perfect forward secrecy is an encryption system that frequently changes the keys used for encryption and decryption. This system ensures that even if one of the most recent keys is compromised, the attack will not be able to spread further, and only a small amount of data will be exposed. 

Contrast this to systems that use a single key for all communication: If that key falls into the wrong hands, the fallout can be disastrous.

With the PFS technology, even cyberattacks such as a man-in-the-middle, a situation where a bad actor infiltrates and possibly changes communication between two parties, are not able to decrypt sessions even after they manage to steal passwords or compromise long-term keys. 

How Does Perfect Forward Secrecy Work?

PFS works by creating a unique key for each communication session, such as a page refresh or a single phone call. These keys are generated by a mathematical algorithm and are only shared between communication parties. 

As mentioned before, even if one key is compromised, the cybercriminals can only access that particular session and not any other communications that may have taken place. This process is known as a key agreement

Key agreement is a protocol for generating cryptographic keys that allow two parties to agree on a secret key without sharing it over an insecure channel. This is important because it means that even if an attacker intercepts communication between the two parties, they will not be able to determine the key and decrypt the message. 

Web servers typically use an encryption key to secure a particular communication session. When a client communicates with the server, it creates a pre-primary secret, and the server’s special key is used to encrypt it. 

The conversation can only be decrypted using the original server key. The team supporting the server needs to keep an eye on all incoming and outgoing messages so it can identify and solve any potential problems.

Perfect forward secrecy is what prevents a malicious actor from using a vulnerability to spy on a conversation undetected.

Perfect Forward Secrecy Protocols 

IPsec (RFC 2412), SSH, and Off-the-Record-Messaging, an instant messaging cryptography protocol, are among the protocol implementations providing perfect forward secrecy, at least optionally.

Perfect forward secrecy is supported by the ephemeral Diffie-Hellman key exchange in Transport Layer Security version 1.3, while OpenSSL utilizes an elliptic curve Diffie-Hellman key exchange.

The Signal Protocol employs the Double Ratchet Algorithm to provide forward secrecy. However, complete forward secrecy is not supported by WPA.

The Case of Heartbleed Bug - Why Perfect Forward Secrecy Is Important 

The Heartbleed bug is one of the best examples of why we need encryption for every online transaction. This bug was discovered in 2012 and disclosed in 2014, when a patch was developed to fix the vulnerability. 

The bug took advantage of a vulnerability in servers that run on OpenSSL instead of directly exploiting sessions. The bad actor managed to steal 64 KB of private memory and run the cyber attack repeatedly, downloading email addresses, cookies, and passwords. 

The problem here was that the single key from a compromised server did not use perfect forward secrecy, which led to an enormous problem for the entire business. Although damage would have been caused even if perfect forward secrecy had been used, the impact would have been much less severe.

Perfect Forward Secrecy Utilization 

As perfect forward secrecy works on sites that support TLS or SSL, its implementation is relatively simple. Both of these cryptographic protocols support secure connections and do not require a key exchange or encryption cipher. 

If you’re getting perfect forward secrecy, both your machine and the server need to agree on a type of encryption. To use the perfect forward secrecy, setting your servers to make the proper cipher suits available is necessary. At the moment, available key exchanges are

The key exchanges are used only once and are deleted after the transaction is complete. The idea is to discourage hackers from obtaining these session keys, as they won’t be of much value to them. 

Perfect Forward Secrecy Benefits 

The main reason you should use perfect forward secrecy is that the protection you’ll get from this type of technology will prevent the hacker from further exploiting your system even when they get a chance to infiltrate it. Perfect forward secrecy will create a unique session key for each transaction, and the hacker’s access to your system will be limited to only that exchange. 

Moreover, enabling this security measure will make it less likely for threat actors to launch an attack against you. Simply put, even when attackers access the private key, they need to put in a lot of effort just to get a small amount of data. Although this isn’t guaranteed protection against a potential attack, it makes you less of an attractive target. 

Perfect Forward Secrecy Drawbacks 

While this technology has much to offer, it is certainly not perfect. For instance, all businesses that want to use perfect forward secrecy must know that their server will need greater processing power as transactions require the generation of unique encryption keys. 

Additionally, if you’re using older operating systems or servers, you won’t be able to implement perfect forward secrecy. It is supported by all browsers and operating systems from Windows XP and later, but if you’re using something older, bear in mind that you will have to make some changes.

Apart from the fact that the attackers cannot see your internal communication, your network team will also be unable to decrypt the traffic. This is another downside, which can be challenging when you need to troubleshoot an issue that demands more time and effort. In the long run, this can affect your business as slowdowns can lead to drops in customer satisfaction.

Backward Secrecy vs. Perfect Forward Secrecy

While perfect forward secrecy guards you against potential incoming attacks and different types of malware, preventing attackers from even managing to launch a threat, backward secrecy’s job is to “heal” sessions and data that were affected in the past. In simple terms, backward secrecy mitigates the damage, while forward secrecy is a preventative tool.

The Bottom Line

With PFS, security is made easier. It is a vital part of keeping your information safe online. By ensuring that each session has its own unique key, PFS makes it much more difficult for hackers to obtain sensitive information. 

You can do several things to ensure your data is protected by PFS, such as using a VPN service or encryption software. Taking these measures can help ensure that your data remains safe and secure.

Why is perfect forward secrecy important?

This technology helps you protect session keys even when the server’s private keys may be at risk. It helps protect past sessions from threats that compromise your passwords or keys. A unique key is created for every session, and even if the key is affected, data not exchanged in that session will not be.


How do you decrypt perfect forward secrecy?

To decrypt PFS sessions, you’ll need to route traffic through TLS devices. Another option is installing an agent on the server. 


Why should I use perfect forward secrecy?

If you are using an SSL or TLS connection, perfect forward secrecy will ensure the session keys are safe even when the private key is hacked. This means that bad actors will not be able to read all your past communications even if they do manage to access a single session.


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