Jithu Sunny: Python script to decipher Caesar ciphers

Caesar cipher is a simple, widely used encryption technique. It is a kind of substitution cipher in which each letter in the plain-message is replaced by a letter some fixed number positions down the alphabet.

Read more - http://en.wikipedia.org/wiki/Caesar_cipher

Example

	Ciphertext: wkh txlfn eurzq ira mxpsv ryhu wkh odcb grj
	Plaintext: the quick brown fox jumps over the lazy dog

view raw example hosted with ❤ by GitHub

Today, I prepared a simple python program to do this for solving a puzzle from Kryptos - an online treasure hunt conducted as a part of MEC EXCEL 2011.

Then I added some more features to it like handling both uppercase and lowercase & ignoring symbols. Here's it.

	#!/usr/bin/python

	#Date: Sept 19, 2011
	#Filename: caesar.py
	#Code for deciphering Caesar-Cipher

	#Author: Jithu Sunny
	#Blog: http://jithusunnyk.blogspot.com/
	#Email: jithusunnyk@gmail.com

	def shift(str, n):
	'''Forms the new string by shifting all characters in str by n places'''
	new = ''
	for c in str:
	if c.isalpha():
	num = ord(c) + n
	if c.islower():
	if num < 123:
	new += chr(num)
	else:
	new += chr(num - 26)
	elif c.isupper():
	if num < 91:
	new += chr(num)
	else:
	new += chr(num - 26)
	else:
	new += c
	return new

	def combi(str):
	'''Prints all 25 possible plain-messages'''
	for i in range(1, 26):
	print shift(str, i)

	str = raw_input('Enter the cipher: ')
	combi(str)

view raw caesar.py hosted with ❤ by GitHub

Sample Output

	jisuka@HCL:~/git/Python/Caesar$ python caesar.py
	Enter the cipher: "Jan hxd fjclqrwp luxbnuh?"
	"Kbo iye gkdmrsxq mvycovi?"
	"Lcp jzf hlenstyr nwzdpwj?"
	"Mdq kag imfotuzs oxaeqxk?"
	"Ner lbh jngpuvat pybfryl?"
	"Ofs mci kohqvwbu qzcgszm?"
	"Pgt ndj lpirwxcv radhtan?"
	"Qhu oek mqjsxydw sbeiubo?"
	"Riv pfl nrktyzex tcfjvcp?"
	"Sjw qgm osluzafy udgkwdq?"
	"Tkx rhn ptmvabgz vehlxer?"
	"Uly sio qunwbcha wfimyfs?"
	"Vmz tjp rvoxcdib xgjnzgt?"
	"Wna ukq swpydejc yhkoahu?"
	"Xob vlr txqzefkd zilpbiv?"
	"Ypc wms uyrafgle ajmqcjw?"
	"Zqd xnt vzsbghmf bknrdkx?"
	"Are you watching closely?"
	"Bsf zpv xbudijoh dmptfmz?"
	"Ctg aqw ycvejkpi enqugna?"
	"Duh brx zdwfklqj forvhob?"
	"Evi csy aexglmrk gpswipc?"
	"Fwj dtz bfyhmnsl hqtxjqd?"
	"Gxk eua cgzinotm iruykre?"
	"Hyl fvb dhajopun jsvzlsf?"
	"Izm gwc eibkpqvo ktwamtg?"