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1 files changed, 62 insertions, 0 deletions

diff --git a/Assignment3/des-demo.py b/Assignment3/des-demo.py
new file mode 100755
index 0000000..0a4954f
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+++ b/Assignment3/des-demo.py
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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:])