Python Script to decode ACER update zips (With auto 16bit key detection)

decode_acer_zip.py

#!/usr/bin/python
#Acer update zip decoder
#Based on information in this post/thread:
#http://forum.xda-developers.com/showpost.php?p=14201285&postcount=161
#As well as "new key" information in
#http://forum.xda-developers.com/showpost.php?p=14505451&postcount=31

import sys
import os
import struct

ZIPHEADER = "PK"

def main():
    if(len(sys.argv) != 3):
        print("Usage:")
        print(sys.argv[0] + " <input encoded zip> <output decoded zip>")
        return

    infile=open(sys.argv[1],"rb")
    outfile=open(sys.argv[2],"wb")

    (key,) = struct.unpack("=H",infile.read(2))
    (seed,) = struct.unpack("=H",ZIPHEADER)
    key = key ^ seed

    print("key= " + hex(key))

    infile.seek(0)

    sys.stdout.write("\n\rReading: " + str(0) )
    buf=infile.read(512)
    pos=512
    while(buf != ""):
        droplast = len(buf) % 2
        if(droplast):
            buf=buf + " "
        block=""
        for x in xrange(0,len(buf),2) :
            (val,)=struct.unpack("=H",buf[x:x+2])
            block=block+struct.pack("=H",(key ^ val) & 0x0000FFFF)
        if(droplast):
            block=block[:-1]
        outfile.write(block)

        sys.stdout.write("\rReading: " + str(pos) )
        pos+=512
        buf=infile.read(512)
    infile.close()
    outfile.close()

    print("\nDone :)")

if(__name__=="__main__"):
    main()