Python implementation of the RC4 algorithm detailed note

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1 # / usr / bin / python
 2 # coding = utf-8
 3 import sys, os, hashlib, time, base64
 4 def rc4 (string, op = ‘encode’, public_key = ‘ddd’, expirytime = 0):
 5 ckey_lenth = 4 #define the length of the IV
 6 public_key = public_key and public_key or ‘‘
 7 key = hashlib.md5 (public_key) .hexdigest () # md5 the password public_key and return a 32-byte key
 8 keya = hashlib.md5 (key [0:16]). Hexdigest () #Made the first 16 bytes of Key md5 and return 32 bytes of keya
 9 keyb = hashlib.md5 (key [16:32]). Hexdigest () #Made the last 16 bytes of the key to md5 and return a 32-byte keyb
10
11 #When encrypting, keyc takes the first 4 bytes of md5 of time.time (), which is used as the IV
12 #When decrypting, take the IV from the first 4 bytes of the ciphertext
13 keyc = ckey_lenth and (op == ‘decode’ and string [0: ckey_lenth] or hashlib.md5 (str (time.time ())). Hexdigest () [32-ckey_lenth: 32]) or ‘‘
14
15 #The real key cryptkey is a 64-byte string obtained by keya splicing keya and keyc's md5
16 cryptkey = keya + hashlib.md5 (keya + keyc) .hexdigest ()
17 key_lenth = len (cryptkey) # 64
18
19 #When encrypting, the plaintext to be encrypted is formed by concatenating the 10 bytes of 0 and the plaintext string to be encrypted with the first 16 bytes of the md5 value of keyb and the plaintext string.
20 #When decrypting, the ciphertext is the content of the first 4 bytes of the incoming string and decoded
21 string = op == ‘decode’ and base64.b64decode (string [4:]) or ‘0000000000’ + hashlib.md5 (string + keyb) .hexdigest () [0:16] + string
22 string_lenth = len (string)
twenty three         
24 result = ‘‘
25 box = list (range (256))
26 randkey = []
27
28 for i in xrange (255):
29 # Randomly fill the ascii code value of the characters in cryptokey, there will be 4 rounds of repetition, randkey [0] ~ randkey [63], randkey [64] ~ randkey [127], ...
30 randkey.append (ord (cryptkey [i% key_lenth]))
31
32 # Randomly shuffle the list of boxes
33 # cryptkey's real purpose is to generate pseudo-random boxes
34 for i in xrange (255):
35 j = 0
36 j = (j + box [i] + randkey [i])% 256
37 tmp = box [i]
38 box [i] = box [j]
39 box [j] = tmp
40
41 for i in xrange (string_lenth):
42 a = j = 0
43 a = (a + 1)% 256
44 j = (j + box [a])% 256
45 tmp = box [a]
46 box [a] = box [j]
47 box [j] = tmp
48 # The above was disrupted again
49
50 #True plaintext string XOR with random value in box to generate encrypted result
51 #No matter how random it is, because cryptkey and string_length are always the same, so the box will eventually be the same.
52 result + = chr (ord (string [i]) ^ (box [(box [a] + box [j])% 256]))
53 #When decrypting, the ciphertext is XORed with the box to return the plaintext
54
55 if op == ‘decode’:
56 #result [10:26] == hashlib.md5 (result [26:] + keyb) .hexdigest () [0:16], used to verify the integrity of the string
57 if (result [0:10] == '0000000000' or int (result [0:10])-int (time.time ())> 0) and result [10:26] == hashlib.md5 (result [26:] + keyb) .hexdigest () [0:16]:
58 return result [26:] #The first ten bytes are 0, the other 16 bytes are the first 16 bytes of md5 of the plaintext string and keyb, and the last is string
59 else:
60 return None
61 else:
62 #Encryption, return base64 encoding of IV + result
63 return keyc + base64.b64encode (result)
64
65 if __name__ == ‘__main__’:
66 #print rc4 (‘we’, 'encode ’,' 98765’)
67 print rc4 (‘fd09GMhYylNXC5t550VwC5oX9WS4zrB0bI9rs6kvTAMoiGI =‘, ’decode’, ’98765’) 

Python implementation of the RC4 algorithm detailed note