105 lines
4.5 KiB
Python
105 lines
4.5 KiB
Python
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#!/usr/bin/python
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##########################
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# cribdrag - An interactive crib dragging tool
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# Daniel Crowley
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# Copyright (C) 2013 Trustwave Holdings, Inc.
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# This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
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# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.
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##########################
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import sys
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import re
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import argparse
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def sxor(ctext,crib):
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# convert strings to a list of character pair tuples
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# go through each tuple, converting them to ASCII code (ord)
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# perform exclusive or on the ASCII code
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# then convert the result back to ASCII (chr)
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# merge the resulting array of characters as a string
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results = []
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single_result = ''
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crib_len = len(crib)
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positions = len(ctext)-crib_len+1
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for index in xrange(positions):
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single_result = ''
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for a,b in zip(ctext[index:index+crib_len],crib):
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single_result += chr(ord(a) ^ ord(b))
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results.append(single_result)
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return results
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def print_linewrapped(text):
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line_width = 40
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text_len = len(text)
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for chunk in xrange(0,text_len,line_width):
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if chunk > text_len-line_width:
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print str(chunk) + chr(9) + text[chunk:]
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else:
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print str(chunk) + chr(9) + text[chunk:chunk+line_width]
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parser = argparse.ArgumentParser(description='cribdrag, the interactive crib dragging script, allows you to interactively decrypt ciphertext using a cryptanalytic technique known as "crib dragging". This technique involves applying a known or guessed part of the plaintext (a "crib") to every possible position of the ciphertext. By analyzing the result of each operation and the likelihood of the result being a successful decryption based on the expected format and language of the plaintext one can recover the plaintext by making educated guesses and adaptive application of the crib dragging technique.')
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parser.add_argument('ciphertext', help='Ciphertext, encoded in an ASCII hex format (ie. ABC would be 414243)')
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parser.add_argument('-c', '--charset', help='A regex-style character set to be used to identify best candidates for successful decryption (ex: for alphanumeric characters and spaces, use "a-zA-Z0-9 ")', default='a-zA-Z0-9.,?! :;\'"')
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args = parser.parse_args()
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ctext = args.ciphertext.decode('hex')
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ctext_len = len(ctext)
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display_ctext = "_" * ctext_len
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display_key = "_" * ctext_len
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charset = '^['+args.charset+']+$'
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response = ''
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while response != 'end':
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print "Your message is currently:"
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print_linewrapped(display_ctext)
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print "Your key is currently:"
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print_linewrapped(display_key)
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crib = raw_input("Please enter your crib: ")
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crib_len = len(crib)
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results = sxor(ctext, crib)
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results_len = len(results)
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#Generate results
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for result_index in xrange(results_len):
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if (re.search(charset,results[result_index])):
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print '*** ' + str(result_index) + ': "' + results[result_index] + '"'
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else:
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print str(result_index) + ': "' + results[result_index] + '"'
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response = raw_input("Enter the correct position, 'none' for no match, or 'end' to quit: ")
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#Replace part of the message or key
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try:
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response = int(response)
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if (response < results_len):
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message_or_key = ''
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while (message_or_key != 'message' and message_or_key != 'key'):
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message_or_key = raw_input("Is this crib part of the message or key? Please enter 'message' or 'key': ")
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if(message_or_key == 'message'):
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display_ctext = display_ctext[:response] + crib + display_ctext[response+crib_len:]
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display_key = display_key[:response] + results[response] + display_key[response+crib_len:]
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elif(message_or_key == 'key'):
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display_key = display_key[:response] + crib + display_key[response+crib_len:]
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display_ctext = display_ctext[:response] + results[response] + display_ctext[response+crib_len:]
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else:
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print 'Invalid response. Try again.'
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except ValueError:
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if (response == 'end'):
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print "Your message is: " + display_ctext
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print "Your key is: " + display_key
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elif (response == 'none'):
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print "No changes made."
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else:
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print "Invalid entry."
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