The Cheltenham Listening Stones are a set of nine sculptures located next to the GCHQ headquarters in Cheltenham, UK. Two of the stones bear an encrypted inscription.

The Navajo code was one of the most successful encryption methods in World War 2. Here are four facts about it you might not have known before.

The pigpen cipher (also known as Freemason’s cipher) is the most popular secret writing alphabet in history. It has been used to encrypt gravestone inscriptions, treasure maps, certificates, testaments, mug inscriptions, beer labels and more. Today, I’m going to introduce ten especially interesting uses.

Little was known about the ciphers of the Unabomber, a highly intelligent serial killer, until the FBI published a detailed description last year. Here’s a summary.

Today I’m going to introduce two encrypted postcards I have recently found on a postcard blog. They are completely different from each other, but both still wait to be solved.