Cryptography with Python – Caesar Cipher
In the last chapter, we have dealt with reverse cipher. This chapter talks about Caesar cipher in detail.
Algorithm of Caesar Cipher
The algorithm of Caesar cipher holds the following features −
Caesar Cipher Technique is the simple and easy method of encryption technique.
It is simple type of substitution cipher.
Each letter of plain text is replaced by a letter with some fixed number of positions down with alphabet.
The following diagram depicts the working of Caesar cipher algorithm implementation −
The program implementation of Caesar cipher algorithm is as follows −
def encrypt(text,s): result = "" # transverse the plain text for i in range(len(text)): char = text[i] # Encrypt uppercase characters in plain text if (char.isupper()): result += chr((ord(char) + s-65) % 26 + 65) # Encrypt lowercase characters in plain text else: result += chr((ord(char) + s - 97) % 26 + 97) return result #check the above function text = "CEASER CIPHER DEMO" s = 4 print "Plain Text : " + text print "Shift pattern : " + str(s) print "Cipher: " + encrypt(text,s)
You can see the Caesar cipher, that is the output as shown in the following image −
The plain text character is traversed one at a time.
For each character in the given plain text, transform the given character as per the rule depending on the procedure of encryption and decryption of text.
After the steps is followed, a new string is generated which is referred as cipher text.
Hacking of Caesar Cipher Algorithm
The cipher text can be hacked with various possibilities. One of such possibility is Brute Force Technique, which involves trying every possible decryption key. This technique does not demand much effort and is relatively simple for a hacker.
The program implementation for hacking Caesar cipher algorithm is as follows −
message = 'GIEWIVrGMTLIVrHIQS' #encrypted message LETTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' for key in range(len(LETTERS)): translated = '' for symbol in message: if symbol in LETTERS: num = LETTERS.find(symbol) num = num - key if num < 0: num = num + len(LETTERS) translated = translated + LETTERS[num] else: translated = translated + symbol print('Hacking key #%s: %s' % (key, translated))
Consider the cipher text encrypted in the previous example. Then, the output with possible hacking methods with the key and using brute force attack technique is as follows −