Implemented LFSR generator with tests and CLI integration

bin/stegano-lsb-set

@@ -115,6 +115,12 @@ if arguments.command != 'list-generators':
         exit(1)
 
     try:
+        if (arguments.generator_function[0] == "LFSR"):
+            # Compute the size of the image for use by the LFSR generator if needed
+            tmp = tools.open_image(arguments.input_image_file)
+            size = tmp.width * tmp.height
+            tmp.close()
+            arguments.generator_function.append(size)
         if (len(arguments.generator_function) > 1):
             generator = getattr(generators, arguments.generator_function[0])(
                 *[int(e) for e in arguments.generator_function[1:]])

stegano/lsbset/generators.py

@@ -173,3 +173,59 @@ def log_gen() -> Iterator[int]:
         adder = max(1, math.pow(10, int(math.log10(y))))
         yield int(y)
         y = y + int(adder)
+
+
+polys = {2: [2, 1],
+         3: [3, 1],
+         4: [4, 1],
+         5: [5, 2],
+         6: [6, 1],
+         7: [7, 1],
+         8: [8, 4, 3, 2],
+         9: [9, 4],
+         10: [10, 3],
+         11: [11, 2],
+         12: [12, 6, 4, 1],
+         13: [13, 4, 3, 1],
+         14: [14, 8, 6, 1],
+         15: [15, 1],
+         16: [16, 12, 3, 1],
+         17: [17, 3],
+         18: [18, 7],
+         19: [19, 5, 2, 1],
+         20: [20, 3],
+         21: [21, 2],
+         22: [22, 1],
+         23: [23, 5],
+         24: [24, 7, 2, 1],
+         25: [25, 3],
+         26: [26, 6, 2, 1],
+         27: [27, 5, 2, 1],
+         28: [28, 3],
+         29: [29, 2],
+         30: [30, 23, 2, 1],
+         31: [31, 3]}
+
+
+def LFSR(m: int) -> Iterator[int]:
+    """LFSR generator of the given size
+    https://en.wikipedia.org/wiki/Linear-feedback_shift_register
+    """
+    n: int = m.bit_length() - 1
+    # Set initial state to {1 0 0 ... 0}
+    state: List[bool] = [0] * n
+    state[0] = 1
+    feedback: bool = 0
+    poly: List[int] = polys[n]
+    while True:
+        # Compute the feedback bit
+        feedback = 0
+        for i in range(len(poly)):
+            feedback = feedback ^ state[poly[i] - 1]
+        # Roll the registers
+        state.pop()
+        # Add the feedback bit
+        state.insert(0, feedback)
+        # Convert the registers to an int
+        out = sum([e * (2**i) for i, e in enumerate(state)])
+        yield out

tests/expected-results/LFSR

@@ -0,0 +1,256 @@
+2
+5
+11
+22
+44
+88
+177
+99
+199
+143
+30
+61
+122
+244
+232
+208
+161
+67
+135
+15
+31
+63
+127
+255
+254
+252
+249
+242
+228
+200
+144
+33
+66
+133
+10
+20
+41
+83
+167
+79
+159
+62
+125
+250
+245
+234
+213
+170
+85
+171
+87
+174
+92
+184
+112
+224
+193
+131
+6
+12
+24
+49
+98
+197
+138
+21
+43
+86
+172
+89
+179
+102
+204
+153
+50
+101
+203
+151
+47
+95
+191
+126
+253
+251
+247
+239
+222
+188
+121
+243
+230
+205
+155
+55
+110
+221
+187
+119
+238
+220
+185
+114
+229
+202
+149
+42
+84
+169
+82
+165
+74
+148
+40
+81
+162
+68
+137
+18
+37
+75
+150
+45
+90
+180
+104
+209
+163
+70
+140
+25
+51
+103
+206
+156
+57
+115
+231
+207
+158
+60
+120
+241
+227
+198
+141
+27
+54
+108
+216
+176
+97
+194
+132
+8
+17
+34
+69
+139
+23
+46
+93
+186
+117
+235
+215
+175
+94
+189
+123
+246
+237
+219
+183
+111
+223
+190
+124
+248
+240
+225
+195
+134
+13
+26
+52
+105
+211
+166
+77
+154
+53
+107
+214
+173
+91
+182
+109
+218
+181
+106
+212
+168
+80
+160
+65
+130
+4
+9
+19
+39
+78
+157
+59
+118
+236
+217
+178
+100
+201
+146
+36
+73
+147
+38
+76
+152
+48
+96
+192
+129
+3
+7
+14
+29
+58
+116
+233
+210
+164
+72
+145
+35
+71
+142
+28
+56
+113
+226
+196
+136
+16
+32
+64
+128
+1
+2

tests/test_generators.py

@@ -128,6 +128,13 @@ class TestGenerators(unittest.TestCase):
             self.assertEqual(next(gen), int(f.readline()))
             self.assertEqual(next(gen), int(f.readline()))
 
+    def test_LFSR(self):
+        """ Test the LFSR generator
+        """
+        with open('./tests/expected-results/LFSR', 'r') as f:
+            self.assertEqual(tuple(itertools.islice(generators.LFSR(2**8), 256)),
+                             tuple(int(line) for line in f))
+
 
 if __name__ == '__main__':
     unittest.main()