Cryptography with Python - ROT13 Algorithm


Till now, you have learnt about reverse cipher and Caesar cipher algorithms. Now, let us discuss the ROT13 algorithm and its implementation.

Explanation of ROT13 Algorithm

ROT13 cipher refers to the abbreviated form Rotate by 13 places. It is a special case of Caesar Cipher in which shift is always 13. Every letter is shifted by 13 places to encrypt or decrypt the message.


The following diagram explains the ROT13 algorithm process pictorially −

ROT13 Algorithm Process

Program Code

The program implementation of ROT13 algorithm is as follows −

from string import maketrans

rot13trans = maketrans('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz', 

# Function to translate plain text
def rot13(text):
   return text.translate(rot13trans)
def main():
   txt = "ROT13 Algorithm"
   print rot13(txt)
if __name__ == "__main__":

You can see the ROT13 output as shown in the following image −



The ROT13 algorithm uses 13 shifts. Therefore, it is very easy to shift the characters in the reverse manner to decrypt the cipher text.

Analysis of ROT13 Algorithm

ROT13 cipher algorithm is considered as special case of Caesar Cipher. It is not a very secure algorithm and can be broken easily with frequency analysis or by just trying possible 25 keys whereas ROT13 can be broken by shifting 13 places. Therefore, it does not include any practical use.