├── README.md
└── rc4.py


/README.md:
--------------------------------------------------------------------------------
 1 |     Copyright (C) 2012 Bo Zhu http://about.bozhu.me
 2 |     
 3 |     Permission is hereby granted, free of charge, to any person obtaining a
 4 |     copy of this software and associated documentation files (the "Software"),
 5 |     to deal in the Software without restriction, including without limitation
 6 |     the rights to use, copy, modify, merge, publish, distribute, sublicense,
 7 |     and/or sell copies of the Software, and to permit persons to whom the
 8 |     Software is furnished to do so, subject to the following conditions:
 9 | 
10 |     The above copyright notice and this permission notice shall be included in
11 |     all copies or substantial portions of the Software.
12 | 
13 |     THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
14 |     IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
15 |     FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
16 |     THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
17 |     LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
18 |     FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
19 |     DEALINGS IN THE SOFTWARE.
20 | 


--------------------------------------------------------------------------------
/rc4.py:
--------------------------------------------------------------------------------
 1 | #!/usr/bin/env python
 2 | 
 3 | """
 4 |     Copyright (C) 2012 Bo Zhu http://about.bozhu.me
 5 | 
 6 |     Permission is hereby granted, free of charge, to any person obtaining a
 7 |     copy of this software and associated documentation files (the "Software"),
 8 |     to deal in the Software without restriction, including without limitation
 9 |     the rights to use, copy, modify, merge, publish, distribute, sublicense,
10 |     and/or sell copies of the Software, and to permit persons to whom the
11 |     Software is furnished to do so, subject to the following conditions:
12 | 
13 |     The above copyright notice and this permission notice shall be included in
14 |     all copies or substantial portions of the Software.
15 | 
16 |     THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 |     IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 |     FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
19 |     THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20 |     LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
21 |     FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
22 |     DEALINGS IN THE SOFTWARE.
23 | """
24 | 
25 | 
26 | def KSA(key):
27 |     keylength = len(key)
28 | 
29 |     S = range(256)
30 | 
31 |     j = 0
32 |     for i in range(256):
33 |         j = (j + S[i] + key[i % keylength]) % 256
34 |         S[i], S[j] = S[j], S[i]  # swap
35 | 
36 |     return S
37 | 
38 | 
39 | def PRGA(S):
40 |     i = 0
41 |     j = 0
42 |     while True:
43 |         i = (i + 1) % 256
44 |         j = (j + S[i]) % 256
45 |         S[i], S[j] = S[j], S[i]  # swap
46 | 
47 |         K = S[(S[i] + S[j]) % 256]
48 |         yield K
49 | 
50 | 
51 | def RC4(key):
52 |     S = KSA(key)
53 |     return PRGA(S)
54 | 
55 | 
56 | if __name__ == '__main__':
57 |     # test vectors are from http://en.wikipedia.org/wiki/RC4
58 | 
59 |     # ciphertext should be BBF316E8D940AF0AD3
60 |     key = 'Key'
61 |     plaintext = 'Plaintext'
62 | 
63 |     # ciphertext should be 1021BF0420
64 |     #key = 'Wiki'
65 |     #plaintext = 'pedia'
66 | 
67 |     # ciphertext should be 45A01F645FC35B383552544B9BF5
68 |     #key = 'Secret'
69 |     #plaintext = 'Attack at dawn'
70 | 
71 |     def convert_key(s):
72 |         return [ord(c) for c in s]
73 |     key = convert_key(key)
74 | 
75 |     keystream = RC4(key)
76 | 
77 |     import sys
78 |     for c in plaintext:
79 |         sys.stdout.write("%02X" % (ord(c) ^ keystream.next()))
80 |     print
81 | 


--------------------------------------------------------------------------------