QR code abuse: when the code is decoded by a computer, we can pervert it by adding moar extra data in chroma...

README.rst

QR Code Abuse

QR code with additional data in grey level.

QR code with additional data in chroma plane.

The problem: you want to use a QR code to convey base information, but want to pass on additional, optional data, that can be reasonably well decoded when the QR code image is transported.

Proposed solutions: use more QR codes, overlaid with the base one. One method is to use chroma planes to transport more data: when decoding from YUV, the Y would not be altered, and the U resp. V planes would contain their own QR codes. Another method is to add layers of QR codes at discrete grey levels, in a way that the value of a pixel is unambiguously the sum of values from different layers.

qrcode-abuse.py

#!/usr/bin/env python
# -*- coding: utf-8 vi:noet
# What if we made crazy QR codes with extra data in chroma...

"""
To reduce flicker, the extra data can be gray-encoded
"""

import sys, struct, ctypes
import cv2
import numpy as np


def gray_enc(value):
	return (value^(value>>1))

def gray_dec(value, bits):
	out = 0
	for idx_bit in range(bits-1, -1, -1):
		out |= (((value >> idx_bit) & 1) ^ ((out >> (idx_bit+1)) & 1)) << idx_bit
	return out

def sbits(value, bits):
	return bin(value | (1<<bits))[3:]

bits = 8
for i in range(1<<bits):
	e = gray_enc(i)
	d = gray_dec(e, bits)
	assert d == i
	continue
	print("%s %s %s" % (
	 sbits(i, bits),
	 sbits(e, bits),
	 sbits(d, bits),
	))


def enc_flt(x):
	b = struct.pack("<f", float(x))
	i = struct.unpack("<I", b)[0]
	g = gray_enc(i)
	return struct.pack("<I", g)

class QREncoder(object):
	def __init__(self):
		self._lib = ctypes.CDLL("libqrencode.so")
		self._lib.QRcode_encodeData.argtypes = ctypes.c_int, ctypes.c_char_p, ctypes.c_int, ctypes.c_int
		class QRCode(ctypes.Structure):
			_fields_ = [
			 ("version", ctypes.c_int),
			 ("width", ctypes.c_int),
			 ("data", ctypes.POINTER(ctypes.c_uint8)),
			]
		self._lib.QRcode_encodeData.restype = ctypes.POINTER(QRCode)
	def encode(self, value):
		assert isinstance(value, bytes)
		version = 2
		level = 3
		qrcode = self._lib.QRcode_encodeData(len(value), value, version, level)
		res = qrcode.contents
		version = int(res.version)
		size = int(res.width)
		data = bytearray(size*size)
		for idx_data in range(size*size):
			data[idx_data] = (1 - (res.data[idx_data] & 1)) * 255
		data = bytes(data)
		self._lib.QRcode_free(qrcode)
		return version, size, data

def make_samesize(datas):
	# make the QR codes the same size (somehow)
	sizes = [None] * len(datas)
	payloads = [None] * len(datas)
	encoder = QREncoder()
	while sizes[0] is None or not reduce(lambda x, y: x and y, map(lambda x: x == sizes[0], sizes)):

		if sizes[0] is not None:
			for idx_data, data in enumerate(datas):
				if sizes[idx_data] < max(sizes):
					datas[idx_data] += b" "


		for idx_data, data in enumerate(datas):
			version, size, data = encoder.encode(data)
			payloads[idx_data] = data
			sizes[idx_data] = size

	return size, payloads

def example_encode_luma():

	datas = []
	datas.append("http://zougloub.eu")
	datas.append("hello world!")
	datas.append("hello again!")
	datas.append("hello ter!")

	size, payloads = make_samesize(datas)

	scale = 16
	img = np.zeros((size+2, size+2), dtype=np.uint8) + 255

	layer_weights = 32, 16, 8, 4, 2

	assert len(datas) <= len(layer_weights)

	img_upd = img[1:-1,1:-1]
	img_qr0 = np.fromstring(payloads[0], dtype=np.uint8).reshape((size, size))
	img_upd[:] = img_qr0

	for idx_data, data in enumerate(payloads[1:]):
		img_qr = np.int32(np.fromstring(data, dtype=np.uint8).reshape((size, size)))
		weight = layer_weights[idx_data]
		comp = img_qr0 != img_qr
		compimg = np.ones_like(img_upd)
		compimg[comp] = weight
		cv2.imwrite("comp-%d.png" % idx_data, compimg)
		img_upd[img_upd >= 128] -= compimg[img_upd >= 128]
		img_upd[img_upd <  128] += compimg[img_upd <  128]
		cv2.imwrite("upd-%d.png" % idx_data, img)

	img = cv2.resize(img, ((size+2)*scale, (size+2)*scale), interpolation=cv2.INTER_NEAREST)
	cv2.imwrite("qrcode-luma.png", img)


def example_encode_chroma():

	datas = []

	datas.append("http://zougloub.eu")

	# some structure...
	extradata = {"x": 1.33}
	# more data with some string encoding

	datas.append("f" + enc_flt(1.33))

	# more data as a string
	datas.append("hello world!")

	assert len(datas) == 3, "Unimplemented"

	size, payloads = make_samesize(datas)

	scale = 16
	img = np.zeros((size+2, size+2), dtype=np.uint8) + 255

	img_upd = img[1:-1,1:-1]
	img_qr0 = np.fromstring(payloads[0], dtype=np.uint8).reshape((size, size))
	img_upd[:] = img_qr0
	img = cv2.merge((img, img, img))

	img_yuv = cv2.cvtColor(img, cv2.COLOR_RGB2YUV)

	for idx_plane in range(1, 3):
		info = payloads[idx_plane]
		img_qr = np.fromstring(info, dtype=np.dtype('B')).reshape((size, size))
		img_upd = img_yuv[1:-1,1:-1,idx_plane]
		img_upd[img_qr0 != img_qr] -= 80

	img = cv2.cvtColor(img_yuv, cv2.COLOR_YUV2RGB)
	img = cv2.resize(img, ((size+2)*scale, (size+2)*scale), interpolation=cv2.INTER_NEAREST)
	cv2.imwrite("qrcode-chroma.png", img)

if __name__ == '__main__':
	example_encode_chroma()
	example_encode_luma()

qrcode-chroma.png

qrcode-luma.png