During a recent CTF I needed to decrypt a page encrypted with a Caesar Cipher. I didn’t know the what the ROT was and I was struggling to find an easy yet useful one around so I wrote this one.
Feel free to borrow it, steal it, claim it as your own or do whatever with it.
norsec0de
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#!/usr/bin/python################################ ## Very Simple Caesar Cipher ## by norsec0de ## ## caesar.py ## ################################import sys
# Encrypt Plain Textdef caesar(plainText, key=0):
cipherText = ""
for c in plainText:
if c.isalpha():
if c.isupper():
caps = True
else:
caps = False
alphabet = ord(c.lower()) + key
if alphabet > ord('z'):
alphabet -= 26
letter = chr(alphabet)
if caps is True:
letter = letter.upper()
cipherText += letter
else:
cipherText += c
return cipherText
# Brute force all 26 possibilities.def guess_caesar(plainText):
print 'Showing all combinations for text ' + plainText
key = 1
for c in range(0,26):
cipherText = caesar(plainText, key)
print 'Key ' + str(key) + ' => ' + cipherText
key += 1
# Main Program# Usageif len(sys.argv) == 1:
print '\nCaesar Cypher Tool'
print '\n Usage: ' + sys.argv[0] + ' (options) <text> <rot key>'
print '\t encrypt => \"Text to encrypt\" <key>'
print '\t decrypt => -d \"Text to decrypt\" <key>'
print '\t decrypt file => -f <filename> <key>'
print '\t brute force => -b \"Cyphertext\" \n'
# Brute forceelif sys.argv[1] == '-b':
plainText = sys.argv[2]
cipherText = guess_caesar(plainText)
print cipherText
# Decode a stringelif sys.argv[1] == '-d':
plainText = sys.argv[2]
key = int(sys.argv[3])
cipherText = caesar(plainText, key)
print cipherText
# Decode a Fileelif sys.argv[1] == '-f':
infile = sys.argv[2]
key = int(sys.argv[3])
with open(infile, "r") as f:
while True:
line = f.readline()
if not line:
break
print caesar(line, key)
# Encode a Stringelse:
plainText = str(sys.argv[1])
key = int(sys.argv[2])
cipherText = caesar(plainText, key)
print '\nEncrypting \"' + plainText + '\" with ROT' + str(key) + " => " + c
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