Python implementation method for RC4 file encryption

This article mainly introduces the python implementation method of RC4 file encryption. The example analyzes the principle of RC4 file encryption and Python implementation skills, for more information about how to implement RC4 file encryption in python, see the following example. Share it with you for your reference. The specific analysis is as follows:

Based on the RC4 stream encryption algorithm, the extended 16*16 S box and 32-byte key are used.
At present, it should be safer.

I just learned python and it's hard to call it.
In addition, it has been implemented in both VC and python. The two platforms can encrypt and decrypt each other, which is very rewarding.

The following is the implementation in python3.0 and needs to be slightly modified under 2.x.

# For python 3.0 # from Libo import struct, sys, OS, binascii "RC4 encryption algorithm 16x16 S box encryption unit: short" def RC4 (pkey, keylen, pin, dlen): N = 65536 S = list (range (N) j = 0 for I in range (N ): j = (j + S [I] + pkey [I % keylen]) % N temp = S [I] S [I] = S [j] S [j] = temp I = j = 0 pout = B ''for x in range (dlen): I = I + 1 j = (j + S [I]) % N temp = S [I] S [I] = S [j] S [j] = temp pout + = struct. pack ('H', pin [x] ^ S [(S [I] + S [j]) % N]) return (p Out) # bytes-> includef Coding (data): if (len (data) % 2): data + = B '\ 0' dlen = len (data) // 2 return (struct. unpack (str (dlen) + 'H', data) # short-> bytesdef unCoding (data): d = B ''for I in range (len (data )): d + = struct. pack ('H', data [I]) return (d) # generate a 32-byte key def CreatKey (Keyt): pl = len (Keyt) key = B ''r = 0 for I in range (32): k = (Keyt [r % pl] + I) % 256 Key + = struct. pack ('B', k) r + = 1 return Key # Update Key def UpdataKey (Keyt): Key = UnCoding (Keyt) # shift Key = Key left loop [1:] + struct. pack ('B', Key [0]) tem = 0 # sum for I in range (len (Key): tem + = Key [I]; keyo = B ''# Xor for I in range (len (Key): Keyo + = struct. pack ('B', (Key [I] ^ tem) % 256) tem + = Keyo [I]> 3 tem = tem % 256 return (Coding (Keyo )) if _ name _ = '_ main _': # obtain the input file if len (sys. argv) = 1: filename = input ('source File: ') else: filename = sys. argv [1] try: fin = open (filename, 'RB') before T: p Rint ('failed to open the file! ') Input () sys. exit () print (filename) # Open the output file if filename [-4:] = '. RC4 ': eID = 1 key = input ('input decryption key :'). encode () ofilename = filename [:-4] else: eID = 2 key = input ('input encryption key :'). encode () ofilename = filename + '. RC4 'key = Coding (CreatKey (key) key = UpdataKey (key) # process duplicate names while OS. path. exists (ofilename): ofilename = OS. path. dirname (ofilename) + '\ replica' + OS. path. basename (ofilename) fout = open (ofilename, 'WB') Print (ofilename) # decrypt if eID = 1: # read file length filelen = struct. unpack ('I', fin. read (4) [0] print ('flielen = ', filelen,' \ n ...... ') while 1: # Read Block size ps = fin. read (2) if not ps: # End of the file break packsize = struct. unpack ('H', ps) [0] # read data dd = fin. read (packsize) # decrypt dd = Coding (dd) x = RC4 (key, len (key), dd, len (dd) key = UpdataKey (key) # crc = struct. unpack ('I', fin. read (4) [0] if binascii. crc32 (x )! = Crc: print ('crc32 verification error! ', Crc, binascii. crc32 (x) input () sys. exit () fout. write (x) # fill the fout at the end of the cropping. truncate (filelen) # encrypted elif eID = 2: # get the file length fin. seek (0, 2) filelen = fin. tell () print ('flielen = ', filelen,' \ n ...... ') fin. seek (0, 0) fout. write (struct. pack ('I', filelen) while 1: # read data dd = fin. read (65534) if not dd: # End of the file break # end filling srl = len (dd) if srl % 2: srl + = 1; dd + = B '\ 0' # crc = struct. pack ('I', binascii. crc32 (dd) # encrypt data dd = Co Ding (dd) x = RC4 (key, len (key), dd, len (dd) key = UpdataKey (key) # write to the file fout. write (struct. pack ('H', srl) fout. write (x) fout. write (crc) fin. close () fout. close () print ('OK! ') Input ()

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