a simple kind of encryption for words is rot13. in rot13, letters of the alphabet are changed with each other using a simple pattern. for example, "a" changes to "n", "b" changes to "o", "c" changes to "p", and so on. each letter is "rotated" by 13 spaces. using the rot13 cipher, the words "simple english wikipedia" becomes "fvzcyr ratyvfu jvxvcrqvn". the rot13 cipher is very easy to decrypt. because there are 26 letters in the english alphabet, if a letter is rotated two times by 13 letters each time, the original letter will be obtained. so applying the rot13 cipher a second time brings back the original text. when he communicated with his army, julius caesar sometimes used what is known as caesar cipher today. this cipher works by shifting the position of letters: each letter is rotated by 3 positions.