Python Implementation Method for RC4 file encryption

Python Implementation Method for RC4 file encryption

This article describes how to implement RC4 file encryption in python. 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.

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# For python 3.0. # From Li Bo Import struct, sys, OS, binascii """ RC4 Encryption Algorithm 16*16 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 (pout) # Bytes-> short Def Coding (data ): If (len (data) % 2 ): Data + = B '\ 0' Dlen = len (data) // 2 Return (struct. unpack (str (dlen) + 'h', data )) # Short-> bytes Def 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 a key Def UpdataKey (Keyt ): Key = unCoding (Keyt) # Shift left of Loop Key = Key [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 __': # Retrieving input files If len (sys. argv) = 1: Filename = input ('source file :') Else: Filename = sys. argv [1]   Try: Fin = open (filename, 'rb ') Except t: Print ('failed to open the file! ') Input () Sys. exit () Print (filename) # Open an 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) + '\ replicase' + OS. path. basename (ofilename) Fout = open (ofilename, 'wb ') Print (ofilename) # Decryption 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 File Break Packsize = struct. unpack ('h', ps) [0] # Read data Dd = fin. read (packsize) # Decryption Dd = Coding (dd) X = RC4 (key, len (key), dd, len (dd )) Key = UpdataKey (key) # Crc 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 position at the end of Cropping Fout. truncate (filelen) # Encryption Elif eID = 2: # Obtain 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 (1, 65534) If not dd: # End of File Break # End Filling Srl = len (dd) If srl % 2: Srl + = 1; Dd + = B '\ 0' # Crc Crc = struct. pack ('I', binascii. crc32 (dd )) # Encrypt data Dd = Coding (dd) X = RC4 (key, len (key), dd, len (dd )) Key = UpdataKey (key) # Writing files Fout. write (struct. pack ('h', srl )) Fout. write (x) Fout. write (crc) Fin. close () Fout. close () Print ('OK! ') Input ()

I hope this article will help you with Python programming.