-
Notifications
You must be signed in to change notification settings - Fork 0
/
Stegosaurus.py
107 lines (91 loc) · 2.97 KB
/
Stegosaurus.py
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
from PIL import Image
import sys
def calculate_bits(P0, P1):
# After the embedding process, the receiver side will
# compute the difference of the ith block d′i=|P′i−P′i+1|
difference = int(abs(P0 - P1))
# The difference d′i is used to search for the number of
# concealed bitstreams in the ith block using the quantization range
# quantization range table
#if 0 <= difference <= 7:
# bits = 3 # R1: pow(2, 3) == 8
# lower = 0
#elif 8 <= difference <= 15:
#bits = 3 # R2: pow(2, 3) == 8
#lower = 8
#elif 16 <= difference <= 31:
#bits = 4 # R3: pow(2, 4) == 16
#lower = 16
#elif 32 <= difference <= 63:
#bits = 5 # R4: pow(2, 5) == 32
#lower = 32
#elif 64 <= difference <= 127:
#bits = 6 # R5: pow(2, 6) == 64
#lower = 64
# elif 128 <= difference <= 255:
# bits = 7 # R5: pow(2, 7) == 128
#lower = 128
if 0 <= difference <= 1:
bits = 1 # R1: pow(2, 1) == 2
lower = 0
elif 2 <= difference <= 3:
bits = 1 # R2: pow(2, 1) == 2
lower = 2
elif 4 <= difference <= 7:
bits = 2 # R2: pow(2, 2) == 4
lower = 4
elif 8 <= difference <= 11:
bits = 2 # R2: pow(2, 2) == 4
lower = 8
elif 12 <= difference <= 15:
bits = 2 # R2: pow(2, 2) == 4
lower = 12
elif 16 <= difference <= 23:
bits = 3 # R2: pow(2, 3) == 8
lower = 16
elif 24 <= difference <= 31:
bits = 3 # R2: pow(2, 3) == 8
lower = 24
elif 32 <= difference <= 47:
bits = 4 # R2: pow(2, 4) == 16
lower = 32
elif 48 <= difference <= 63:
bits = 4 # R2: pow(2, 4) == 16
lower = 48
elif 64 <= difference <= 95:
bits = 5 # R2: pow(2, 5) == 32
lower = 64
elif 96 <= difference <= 127:
bits = 5 # R2: pow(2, 5) == 32
lower = 96
elif 128 <= difference <= 191:
bits = 6 # R2: pow(2, 6) == 64
lower = 128
elif 192 <= difference <= 255:
bits = 6 # R2: pow(2, 6) == 64
lower = 192
# The secret bitstreams are obtained after converting the
# decimal value of (d′i−loweri) into binary form.
secret = difference - lower
secret_bitstream = bin(secret)[2:].zfill(bits)
assert (len(secret_bitstream) == bits)
return secret_bitstream
def split_every_n(line, n):
return [line[i:i+n] for i in range(0, len(line), n)]
def bin2ascii(inputs):
return ''.join(map(lambda x: chr(int(x, 2)),
split_every_n(inputs, 8)))
filename = 'flag.png'
im = Image.open(filename).convert('RGB')
pix = im.load()
width, height = im.size
msg = ''
for h in range(0, height):
for w in range(1, width, 2):
# zig zag by going reversed order every odd row
if (h % 2 == 1):
w = (-w) % width
r, g, b = pix[w, h]
pr, pg, pb = pix[w-1, h]
msg += calculate_bits(b, pb)
print(bin2ascii(msg))