PDFHider.py

#!/usr/bin/python
#
#written for Python 2.7
#
#Pedro Sicilia
#Nicholas Tateo
#CIS4362
#PDFHider: PDF angecryption CLI tool 
#
#Usage: ./PDFHide [hidden.pdf] [cover.pdf] [combined.pdf]
#	-Output file combined.pdf will contain encrypted data from hidden.pdf
#		but will display as cover.pdf, can be decrypted to show hidden.pdf
#
#Encrypt: ./PDFHide -e [combined.pdf]
#	-intakes user-specified file and encrypts to reveal the other pdf
#
#Decrypt: ./PDFHide -d [combined.pdf]
#	-intakes user-specified file and decrypts to reveal the other pdf
#

import sys
from Crypto.Cipher import AES

c0 =  "%PDF-obj\nstream\n"
chunk_end = "\nendstream\nendobj\n"
CHUNK_END_SIZE = len(chunk_end)
cphr = AES
pdfmagic = "%PDF-"
sym_key = "ABCDEFGHIJKLMNOP"
EOF = "%%EOF"
EOF_SIZE = len(EOF)

#takes argument vector as parameter
def checkArgs(v):
	if(len(v) == 4):
		return True
	elif(len(v) > 4):
		print "Error: excess arguments\n"
	elif(len(v) < 3):
		print "Error: missing arguments\n" 

	return False
	
#takes argument vector as parameter
def checkFlag(v):
	if(len(v) > 1 and v[1][0] != '-'):
		return False
	else:
		if(len(v) != 3):
			print "Error: number of arguments\n"
			return False
		else:
			if(v[1] == "-e"):
				enc(v[2])
			elif(v[1] == "-d"):
				dec(v[2])
			else:
				print "Error: unknown flag\n"
				return False
				
		return True

#encrypts result file
def enc(file):
	with open(file, "rb") as input:
		data = input.read()
		
	print "Encrypting file", file, "\nWriting output to encrypted.pdf\n"
	
	#retrieve and remove IV
	iv = data[(-cphr.block_size):]
	data = data[:(-cphr.block_size)]
	
	cbc_e = cphr.new(sym_key, cphr.MODE_CBC, iv)
	enc = cbc_e.encrypt(data)
	
	i = (enc.find(pdfmagic, cphr.block_size))
	
	#insert dummy chunk ending and IV
	enc = enc[:i] + chunk_end + enc[i:] + iv

	with open("encrypted.pdf", "w") as o:
		o.write(enc)

#decrypts result file
def dec(file):
	with open(file, "rb") as input:
		data = input.read()

	print "Decrypting file", file, "\nWriting output to decrypted.pdf\n"

	#remove dummy chunk ending
	i = (data.find(pdfmagic, cphr.block_size))
	dec = data[:(i - CHUNK_END_SIZE)] + data[i:]
	
	#retrieve and remove IV
	iv = dec[(-cphr.block_size):]
	dec = dec[:(-cphr.block_size)]

	cbc_d = cphr.new(sym_key, cphr.MODE_CBC, iv)	
	dec = cbc_d.decrypt(dec)
	
	dec += iv
	with open("decrypted.pdf", "w") as o:
		o.write(dec)

#pads data to a multiple of cipher block size
def pad(fdata):
	return fdata + ((cphr.block_size - len(fdata) % cphr.block_size) * chr(cphr.block_size - len(fdata) % cphr.block_size)).encode()

#----------Begin main script----------

if(checkFlag(sys.argv)):
	print "Successfully converted file!"
	
elif(checkArgs(sys.argv)):
	infile1, infile2, outfile = sys.argv[1:4]
	
	with open(infile1, "rb") as input:
		infile1 = pad(input.read())
		
	with open(infile2, "rb") as input:
		infile2 = pad(input.read())
	
	ptxt = infile1[:cphr.block_size]
	
	ecb = cphr.new(sym_key, cphr.MODE_ECB)
	c0 = ecb.decrypt(c0.encode())
	
	initV = ""

	for i in range(cphr.block_size):
		x = ord(c0[i]) ^ ord(ptxt[i])
		initV += chr(x)
	
	cbc_init = cphr.new(sym_key, cphr.MODE_CBC, initV)

	combo = cbc_init.encrypt(infile1)
		
	combo = combo + chunk_end + infile2 + initV
	
	with open(outfile, "w") as o:
		o.write(combo)
	
	print "\nSuccessfully wrote combined file", outfile

print("\nExiting...\n")

#-----------------End-----------------