This little GTK application enables encrypting text with the Caesar method (shifting a→b, b→ c, ..., z→ a) as well as decrypting text encrypted with Caesar without knowledge of the number of shifts. This is done by comparing the frequency of letters with the common English letter frequencies and searching for the smallest mean square error in the difference of frequencies.
Clone the repository and open it with GNOME Builder. Then, run or install. The button "encrypt" shifts the text in the field by one, "decrypt" tries to reverse the effects. Make sure the text is long enough for the statistical methods to be successful.