F4.py
4.49 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
__author__ = 'chunk'
import time
import numpy as np
import numpy.random as rnd
from msteg import *
import mjsteg
import pyjpegobj
from common import *
class F4(StegBase):
""" This module has two methods: <i>embed_raw_data</i> to embed data
with the F3 algorithm and <i>extract_raw_data</i> to extract data
which was embedded previously. """
def __init__(self, key=sample_key):
"""
Constructor of the F3 class.
"""
StegBase.__init__(self, key)
def _get_cov_data(self, img_path):
"""
Returns DCT coefficients of the cover image.
"""
self.cov_jpeg = pyjpegobj.Jpeg(img_path, key=self.key)
cov_data = self.cov_jpeg.getsignal(channel='Y')
self.cov_data = np.array(cov_data, dtype=np.int16)
return self.cov_data
def embed_raw_data(self, src_cover, src_hidden, tgt_stego):
self.t0 = time.time()
try:
cov_data = self._get_cov_data(src_cover)
hid_data = self._get_hid_data(src_hidden)
# print hid_data.dtype,type(hid_data),hid_data.tolist()
cov_data, bits_cnt = self._raw_embed(cov_data, hid_data)
if bits_cnt != np.size(hid_data) * 8:
raise Exception("Expected embedded size is %db but actually %db." % (
np.size(hid_data) * 8, bits_cnt))
self.cov_jpeg.setsignal(cov_data, channel='Y')
self.cov_jpeg.Jwrite(tgt_stego)
# size_cov = os.path.getsize(tgt_stego)
size_cov = np.size(cov_data) / 8
size_embedded = np.size(hid_data)
self._display_stats("embedded", size_cov, size_embedded,
time.time() - self.t0)
except TypeError as e:
raise e
except Exception as expt:
print "Exception when embedding!"
raise
def extract_raw_data(self, src_steg, tgt_hidden):
self.t0 = time.time()
try:
steg_data = self._get_cov_data(src_steg)
# emb_size = os.path.getsize(src_steg)
emb_size = np.size(steg_data) / 8
# recovering file size
header_size = 4 * 8
size_data, bits_cnt = self._raw_extract(steg_data, header_size)
if bits_cnt < header_size:
raise Exception("Expected embedded size is %db but actually %db." % (
header_size, bits_cnt))
size_data = bits2bytes(size_data)
size_hd = 0
for i in xrange(4):
size_hd += size_data[i] * 256 ** i
raw_size = size_hd * 8
if raw_size > np.size(steg_data):
raise Exception("Supposed secret data too large for stego image.")
hid_data, bits_cnt = self._raw_extract(steg_data, raw_size)
if bits_cnt != raw_size:
raise Exception("Expected embedded size is %db but actually %db." % (
raw_size, bits_cnt))
hid_data = bits2bytes(hid_data)
# print hid_data.dtype,type(hid_data),hid_data.tolist()
hid_data[4:].tofile(tgt_hidden)
self._display_stats("extracted", emb_size,
np.size(hid_data),
time.time() - self.t0)
except Exception as expt:
print "Exception when extracting!"
raise
def _raw_embed(self, cov_data, hid_data):
"""
cov_data - 1-D numpy.int16 array (permunated)
hid_data - 1-D numpy.uint8 array
"""
hid_data = bytes2bits(hid_data)
i = 0
for x in np.nditer(cov_data, op_flags=['readwrite']):
if x == 0: continue
m = (hid_data[i] & 1)
if x > 0 and x & 1 != m:
x[...] -= 1
elif x < 0 and x & 1 == m:
x[...] += 1
if x == 0: continue
i += 1
if i == hid_data.size: break
return cov_data, i
def _raw_extract(self, steg_data, num_bits):
"""
Just a small helper function to extract hidden data.
steg_data - 1-D numpy.int16 array (permunated)
"""
hid_data = np.zeros(num_bits, np.uint8)
j = 0
for x in steg_data:
if x == 0: continue
if j >= num_bits: break
if x > 0:
hid_data[j] = x & 1
else:
hid_data[j] = (x & 1) ^ 1
j = j + 1
return hid_data, j
def __str__(self):
return "F4"