## How does ROT13 work?

Applying ROT13 we replace each letter in a message by its partner 13 characters further along the alphabet. Thus, we replace a with n, b with o, c with p, and so on. Here’s the full mapping:

ROT13 is a special case of Caesar cipher using the basic Latin alphabet (a-z) and a shift of 13 letters. As the alphabet consists of 26 letters ($2\cdot 13$) we can undo the operation (decode) by applying the same algorithm. This makes ROT13 is its own inverse.

## Where is ROT13 being used today?

Today, ROT13 is often found on social media platforms as a means of hiding spoilers and problem solutions from the casual glance. It has been described as the “Usenet equivalent of printing an answer to a quiz upside down” as it provides virtually no cryptographic security.