read_qrcode.py

"""
This is the read_qrcode module for the vending machine. It uses a ZBar image 
processor to scan a video stream for a QR Code. it then decodes the image and 
processes the data embedded in it.
"""

from Crypto.Hash import MD5
from sys import argv
import base64
import cPickle as Pickle
import zbar
from motor_control import motor_switch

def read(challenge_code, motor_num):
    
    # create a Processor
    proc = zbar.Processor()
    
    # configure the Processor
    proc.parse_config('enable')
    
    # initialize the Processor
    device = '/dev/video0'
    if len(argv) > 1:
        device = argv[1]
    proc.init(device)
    
    # setup a callback
    def my_handler(proc, image, closure):
        # extract results
        for symbol in image:
            if not symbol.count:
                # do something useful with results
                process_code(symbol.data, challenge_code, motor_num)
    
    proc.set_data_handler(my_handler)
    
    # enable the preview window
    proc.visible = True
    
    # initiate scanning
    proc.active = True
    try:
        proc.process_one()
        #proc.user_wait()
    except zbar.WindowClosed:
        pass
     
     
def process_code(verify_code, challenge_code, motor):     
    
    #Load the keys from a file
    server_pub_key = Pickle.load(open("server_key.pub", 'r'))

    vending_priv_key = Pickle.load(open("vending_key.priv", 'r'))
    
    #Process, decode, decrypt and verify the data
    verify_code = verify_code.split('[]', 2)
    encoded_string = verify_code[0].split('**', 2)
    encoded_signature = verify_code[1].split('**', 2)

    encrypted_string = (base64.b64decode(encoded_string[0]), base64.b64decode(encoded_string[1]))
    signature = (long(base64.b64decode(encoded_signature[0])), long(base64.b64decode(encoded_signature[1])))
    
    decrypted_message = vending_priv_key.decrypt(encrypted_string)
    hash_code = MD5.new(decrypted_message[4:8]).digest()
    
    verify_test = server_pub_key.verify(hash_code, signature)

    if decrypted_message[4:8] != challenge_code:
        print 'Invalid QR-Code. Please try again.'
    
        if verify_test != True:
            print 'The source of this QR-code could not be verified. Please try again.'

    else:
        print "Thank you for your purchase. Enjoy your day :)"
        
        motor_switch(motor)