Ciphers, Algorithms and Negotiating Security Settings

Here’s what you need to know about the algorithms behind SSL/TLS encryption.

If you study SSL and encryption long enough, eventually you’re going to come across the word “cipher.” Aside from just generally being a cool word, ciphers are a very important part of encryption.

So, what are encryption ciphers?

Ciphers are algorithms, more specifically they’re a set of steps for both performing encryption as well as the corresponding decryption. Nowadays ciphers are dependent upon the advanced processing capabilities of computers. That hasn’t always been the case though. One of the first, well-known historical ciphers belonged to Caesar – emperor of Rome and purveyor of fancy appetizer salads – who used it to communicate with his generals during military operations.

Over the years, ciphers have become more complex, but the logic behind them has stayed the same. Whether it was Caesar crossing the Rubicon, the infamous Enigma cipher of World War II or some of the algorithms of today—the idea has always been to encode or encipher a message in such a way that only the intended party can read it.

Two Kinds of Ciphers

For all intents and purposes, when we discuss ciphers as they relate specifically to SSL encryption, there are two kinds of algorithms: symmetric and asymmetric. This really comes down to the kind of encryption you’re going to be performing, again, symmetric or asymmetric.

Symmetric encryption involves two keys that are the same, or as the name quite cleverly implies, symmetric. Both keys can perform both functions: encryption and decryption. You see this during an encrypted web connection between a browser and a server. After the SSL certificate has been authenticated and the SSL handshake is complete, the browser and server exchange symmetric “session keys” that allow them to communicate securely for the duration of the visit. While these session keys are in play, they are making use of a symmetric cipher.

Conversely, with…

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