2-4-3desforfile.py

from Crypto.Cipher import DES3
from Crypto.Hash import SHA256 as SHA
from os import path

KSIZE = 1024

class myDES():
	def __init__(self, keytext, ivtext):
		hash = SHA.new()
		hash.update(keytext.encode('utf-8'))
		key = hash.digest()	
		self.key = key[:24]
		
		hash.update(ivtext.encode('utf-8'))
		iv = hash.digest()
		self.iv = iv[:8]		
	
	def makeEncInfo(self, filename):
		fillersize = 0
		filesize = path.getsize(filename)			
		if filesize%8 != 0:
			fillersize = 8-filesize%8
			
		filler = '0'*fillersize
		header = '%d' %(fillersize)
		gap = 8-len(header)
		header += '#'*gap		
		
		return header, filler		

	def enc(self, filename):
		encfilename = filename + '.enc'
		header, filler = self.makeEncInfo(filename)		
		des3 = DES3.new(self.key, DES3.MODE_CBC, self.iv)
		
		h = open(filename, 'rb')
		hh = open(encfilename, 'wb+')		
		
		enc = header.encode('utf-8')				
		content = h.read(KSIZE)
		content = enc + content
		while content:			
			if len(content) < KSIZE:
				content += filler.encode('utf-8')			
		
			enc = des3.encrypt(content)			
			hh.write(enc)			
			content = h.read(KSIZE)
				
		h.close()
		hh.close()		
		
	def dec(self, encfilename):
		filename = encfilename + '.dec'
		des3 = DES3.new(self.key, DES3.MODE_CBC, self.iv)
				
		h = open(filename, 'wb+')
		hh = open(encfilename, 'rb')
		
		content = hh.read(8)
		dec = des3.decrypt(content)
		header = dec.decode()
		fillersize = int(header.split('#')[0])
		
		content = hh.read(KSIZE)		
		while content:
			dec = des3.decrypt(content)
			if len(dec) < KSIZE:
				if fillersize != 0:
					dec = dec[:-fillersize]
			
			h.write(dec)
			content = hh.read(KSIZE)	
				
		h.close()
		hh.close()	

def main():
	keytext = 'samsjang'
	ivtext = '1234'
	filename = 'plain.txt'	
	encfilename = filename + '.enc'
	
	myCipher = myDES(keytext, ivtext)
	myCipher.enc(filename)
	myCipher.dec(encfilename)	
	
if __name__ == '__main__':
	main()