VD625 Config Decrypt

import sys
from Crypto.Cipher import AES
import hashlib
import zlib
import binascii

def sercomm_hexdigest(s):
    # Replicates a really odd behaviour in the Sercomm libfwutil implementation of hex-digest to hex-string
    # Hexadecimal digits starting prefixed with a '0' have their leading zero removed and are followed by a trailing null byte.
    hex_s = ''
    for c in s:
        c_hex = c.encode('hex')
        if c_hex.startswith('0'):
            hex_s += c_hex[1:]
            hex_s += '\x00'
        else:
            hex_s += c_hex
    return hex_s
def keyPermutator(key):
    perm_tbl = '26aejsw37bfktx48chmuy59dipvz'
    key = bytearray(key)
    for i in xrange(len(key)):
        key[i] = perm_tbl[key[i] % len(perm_tbl)]
    return str(key)

def getKeyPair(a0="",a1="",a2="",kf=""):
    digest_1 = hashlib.new('md5')
    digest_1.update(a0)
    digest_1.update(a1)
    digest_2 = hashlib.new('md5')
    digest_2.update(a0)
    digest_2.update(a2)
    digest_3 = hashlib.new('md5')
    digest_3.update(a1)
    digest_3.update(a2)
    digest_fin = hashlib.new('md5')
    digest_fin.update(digest_1.digest())
    digest_fin.update(digest_2.digest())
    digest_fin.update(digest_3.digest())
    key = keyPermutator(sercomm_hexdigest(digest_fin.digest()))
    return dict(key=key, iv='\x00' * 32)
if __name__ == "__main__":
    binfile=''
    k=getKeyPair(a0='sErCoMm',a1='vD625',a2='AGCOMBO')
    print "KEY: %s" % (k['key'])
    #decrypt file
    with open(sys.argv[1]) as f:
        while True:
            c = f.read(2)
            if not c:
                break
            r=int(c,16)
            binfile+=chr(r)
    decrypted=open(sys.argv[1]+".decrypted","wb")
    aes = AES.new(key=k['key'], mode=AES.MODE_CBC, IV=k['iv'][16:])
    plaintext_body = aes.decrypt(binfile)
    print "HEADER: %s" % (binascii.hexlify(plaintext_body[:32]))
    decrypted.write(zlib.decompress(plaintext_body[32:]))
    decrypted.close()
    print "Output file: %s.decrypted" % (sys.argv[1])