moth/packages/steg/100/encode

#! /usr/bin/python

## Fetch some public domain images, make a PNG of the key, and encode
## that in the Exif.Image.OriginalRawFileData tags of the images

import os
import glob
import random
import shutil
import md5
import sys
import zipfile

def system(cmd):
    ret = os.system(cmd)
    if ret:
        raise OSError('return value %d: %s' % (ret, cmd))

# Read in key image
key_png = sys.stdin.read()

# Duplicate two photos, give them a chance to bindiff
jpegs = sys.argv[1:]
random.shuffle(jpegs)
for fn in jpegs[:2]:
    root, ext = os.path.splitext(fn)
    jpegs.append(fn)
random.shuffle(jpegs)

bytes_per_photo = len(key_png) / len(jpegs)

zipf = zipfile.ZipFile(sys.stdout, 'w')
for i in range(len(jpegs)):
    fn = jpegs[i]

    cmd1 = 'set Exif.Canon.0x0019 %d' % i

    offset = i * bytes_per_photo
    if i == len(jpegs) - 1:
        bytes = key_png[offset:]
    else:
        bytes = key_png[offset:offset + bytes_per_photo]
    bytes_str = ' '.join(str(ord(c)) for c in bytes)
    cmd2 = 'set Exif.Canon.0x0018 "%s"' % bytes_str

    # Now apply our devious stuff
    system('exiv2 -M\'%s\' -M\'%s\' %s' % (cmd1, cmd2, fn))

    # Read it in
    contents = open(fn, 'rb').read()

    # Find the new file's md5 checksum
    checksum = md5.new(contents).hexdigest()

    # Make a new zip file entry
    zi = zipfile.ZipInfo(checksum + '.jpg')
    zi.compress_type = zipfile.ZIP_DEFLATED
    zi.external_attr = 0644 << 16L
    zipf.writestr(zi, contents)