StegEncoder/FileType.py at master · mihai-bontea/StegEncoder · GitHub

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
from math import ceil
from time import time
from typing import List
import numpy as np

SKIP_BYTES = True

class FileType:

    @staticmethod
    def encode_message_in_carrier_bytes_skip(
        carrier: bytes,
        secret_message: bytes,
        skip_over: int
    ) -> bytes:
        message_length = len(secret_message)
        new_secret_message_len_in_bytes = skip_over * (message_length * 8 - 1) + message_length * 8

        payload_bits = np.unpackbits(
            np.frombuffer(secret_message, dtype=np.uint8, count=message_length)
        )

        carrier_bits = np.unpackbits(
            np.frombuffer(carrier, dtype=np.uint8, count=new_secret_message_len_in_bytes).view(np.uint8)
        ).reshape(new_secret_message_len_in_bytes, 8)

        payload_index = 0
        for carrier_index in range(0, len(carrier_bits), (skip_over + 1)):
            carrier_bits[carrier_index][7] = payload_bits[payload_index]
            payload_index += 1

        return np.packbits(carrier_bits).tobytes() + carrier[new_secret_message_len_in_bytes:]

    @staticmethod
    def encode_message_in_carrier_list_skip(
        carrier: List[np.uint8],
        secret_message: bytes,
        bytes_available: int
    ) -> List[np.uint8]:
        """
        Returns the modified carrier bytes after the secret message has been encoded inside with
        the skip bytes feature enabled.
        """
        message_length = len(secret_message)
        skip = 0
        while skip * (message_length * 8 - 1) + len(secret_message) * 8 <= bytes_available:
            skip += 1

        new_secret_message_len_in_bytes = skip * (message_length * 8 - 1) + message_length * 8
        carrier_bytes = np.array(carrier[:new_secret_message_len_in_bytes], dtype=np.uint8).tobytes()
        modified = FileType.encode_message_in_carrier_bytes_skip(carrier_bytes, secret_message, skip)
        carrier[:new_secret_message_len_in_bytes] = np.frombuffer(modified, dtype=np.uint8).tolist()
        return carrier

    @staticmethod
    def encode_message_in_carrier_bytes(
        carrier: bytes,
        secret_message: bytes,
        nr_lsb_used: int
    ) -> bytes:
        message_length = len(secret_message)
        payload_bits = np.zeros(shape=(message_length, 8), dtype=np.uint8)
        payload_bits[:message_length, :] = np.unpackbits(
            np.frombuffer(secret_message, dtype=np.uint8, count=message_length)
        ).reshape(message_length, 8)

        bytes_modified = int(ceil(message_length * 8 / nr_lsb_used))
        payload_bits.resize(bytes_modified * nr_lsb_used)

        carrier_bits = np.unpackbits(
            np.frombuffer(carrier, dtype=np.uint8, count=bytes_modified).view(np.uint8)
        ).reshape(bytes_modified, 8)

        carrier_bits[:, 8 - nr_lsb_used : 8] = payload_bits.reshape(
            bytes_modified, nr_lsb_used
        )

        return np.packbits(carrier_bits).tobytes() + carrier[bytes_modified :]

    @staticmethod
    def encode_message_in_carrier_list(
        carrier: List[np.uint8],
        secret_message: bytes,
        nr_lsb_used: int
    ) -> List[np.uint8]:
        """
        Returns the modified carrier bytes after the secret message has been encoded inside.
        """
        rightmost_bit_index = int(ceil(len(secret_message) * 8 / nr_lsb_used))
        carrier_bytes = np.array(carrier[:rightmost_bit_index], dtype=np.uint8).tobytes()

        modified = FileType.encode_message_in_carrier_bytes(carrier_bytes, secret_message, nr_lsb_used)
        carrier[:rightmost_bit_index] = np.frombuffer(modified, dtype=np.uint8).tolist()
        return carrier

    @staticmethod
    def decode_message_from_carrier(
        carrier: List[np.uint8],
        message_len_in_bits: int,
        nr_lsb_used: int
    ) -> bytes:
        """
        Returns the bytes of te secret message stored inside the carrier bytes.
        """
        message_len_in_bytes = int(ceil(message_len_in_bits / nr_lsb_used))
        carrier_bytes = np.array(carrier[:message_len_in_bytes], dtype=np.uint8).tobytes()
        message_bits = np.unpackbits(
            np.frombuffer(carrier_bytes, dtype=np.uint8, count=message_len_in_bytes).view(np.uint8)
        ).reshape(message_len_in_bytes, 8)[:, 8 - nr_lsb_used : 8]
        return np.packbits(message_bits).tobytes()[: message_len_in_bits // 8]

    @staticmethod
    def decode_message_from_carrier_skip(
        carrier: List[np.uint8],
        message_len_in_bits: int,
        bytes_available: int
    ) -> bytes:
        """
        Returns the bytes of the secret message stored inside the carrier bytes with the skip bytes feature enabled.
        """
        skip = 0
        while skip * (message_len_in_bits - 1) + message_len_in_bits <= bytes_available:
            skip += 1

        new_secret_message_len = skip * (message_len_in_bits - 1) + message_len_in_bits
        carrier_bytes = np.array(carrier[:new_secret_message_len], dtype=np.uint8).tobytes()

        message_bits = np.unpackbits(
            np.frombuffer(FileType.skip_carrier_bytes(carrier_bytes, skip), dtype=np.uint8, count=message_len_in_bits).view(np.uint8)
        ).reshape(message_len_in_bits, 8)[:, 8 - 1 : 8]
        return np.packbits(message_bits).tobytes()[: message_len_in_bits // 8]

    @staticmethod
    def skip_carrier_bytes(
        carrier_bytes: bytes,
        skip_over: int
    ) -> bytes:
        """
        Returns the bytes of the carrier that actually contain bits from the secret message,
        jumping over 'skip_over' unmodified bytes.
        """
        temp = bytearray()
        for index in range(0, len(carrier_bytes), skip_over + 1):
            temp.append(carrier_bytes[index])
        return bytes(temp)