I had a course called Security and Forensic Computing with Professor Bill Buchanan of Napier University. One of the first topics was the use of different cipher methods.
The most basic cipher is the Caesar cipher – which is said to have been used by Julius Caesar to encrypt his private correspondence. The idea is that each letter is moved a certain number of positions down the alphabet. A bit more sophisticated is the scrambled alphabet – which scrambles the mapping of the charters, making it much harder to decode.
It is however possible to decode a scrambled alphabet code by the likelihood of a certain letter being used in a word. For example the letter e will be the most used letter in the English language, after that the letter t is the most used. Also certain words will appear more often than others, which will give away some of the code. I had an assignment in class, to try to crack some code in this way. I thought this would be a great project to dust off my limited PHP skills.
The result can be seen at: https://ifconfig.dk/scrambledalphabet.php. Further reading on the subject can be done here.