52 lines
1.9 KiB
Python
52 lines
1.9 KiB
Python
from utils import CipherUtils
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CLEAR_LIST = [0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1]
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INIT_STATE = [0, 1, 1, 0]
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COEFFICIENTS = [1, 1, 1, 0]
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def create_shift_register(init_state: [int], coefficients: [int]) -> [int]:
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"""
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Creates and returns the maximum bit stream for the given input state via a linear shift register.
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Especially the coefficients are important as choosing the correct ones for any given shift register length
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will provide the maximum amount of bits before they repeat
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:param init_state: The initial bits in the shift register
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:param coefficients: The coefficients of every field in the shift register
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:return: The maximum length bit stream generated by the linear shift register
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"""
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return_list = []
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current_state = init_state.copy()
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if (size := len(init_state)) != len(coefficients):
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print('Length of lists does not match.')
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exit()
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for x in range(2 ** size):
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return_list.append(current_state[-1])
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new_state_value = 0
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for i in range(size):
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new_state_value = (new_state_value + current_state[i] * coefficients[i]) % 2
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current_state.insert(0, new_state_value)
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current_state.pop(-1)
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if current_state == init_state:
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# For ideal coefficients, the output is perfectly fine.
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# However, for unideal coefficients, it might appear that we reach a state after lets say 1 iteration.
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# We still need to output [size] amount of bits, hence the following line.
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if x != (2 ** size) - 2:
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return_list.extend(current_state[1:][::-1])
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break
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return return_list
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if __name__ == '__main__':
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key = create_shift_register(INIT_STATE, COEFFICIENTS)
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encrypted = CipherUtils.xor_two_lists(CLEAR_LIST, key)
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decrypted = CipherUtils.xor_two_lists(encrypted, key)
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print(CLEAR_LIST)
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print(encrypted)
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print(decrypted)
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