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#!/usr/bin/python
# Copyright (c) 2015 Camil Staps <info@camilstaps.nl>
import sys, getopt, binascii
from Crypto.Cipher import DES
def main(argv):
key = ''
plaintext = ''
ciphertext = ''
# Parse arguments. Use -h for help.
try:
opts, args = getopt.getopt(argv, "hk:p:c:", ["key=","plaintext=","ciphertext="])
except getopt.GetoptError:
usage()
sys.exit(2)
for opt, arg in opts:
if opt == '-h':
usage()
sys.exit()
elif opt in ("-k", "--key"):
key = binascii.a2b_hex(arg)
elif opt in ("-p", "--plaintext"):
plaintext = binascii.a2b_hex(arg)
elif opt in ("-c", "--ciphertext"):
ciphertext = binascii.a2b_hex(arg)
if key == '' or plaintext == '' and ciphertext == '':
usage()
sys.exit(2)
# PyCrypto does the hard work
cipher = DES.new(key, DES.MODE_ECB)
encryption = ''
decryption = ''
if plaintext != '':
encryption = cipher.encrypt(plaintext)
if ciphertext != '':
decryption = cipher.decrypt(ciphertext)
# When plaintext and ciphertext are provided, output if DES[k](p) = c. Otherwise, output the encryption / decryption.
if encryption != '' and decryption != '':
print encryption == ciphertext
elif encryption != '':
print binascii.b2a_hex(encryption)
elif decryption != '':
print binascii.b2a_hex(decryption)
def usage():
print 'Usage: des-demo.py -k <key> [-p <plaintext>] [-c <ciphertext>]'
print ' key : an 8-byte value entered as hexadecimal numbers'
print ' plaintext : an 8-byte value entered as hexadecimal numbers'
print ' ciphertext : an 8-byte value entered as hexadecimal numbers'
print 'At least one of plaintext and ciphertext should be provided. When both are provided, we check if DES[k](p) = c.'
if __name__ == "__main__":
main(sys.argv[1:])
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