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103 lines
3.1 KiB
Python
103 lines
3.1 KiB
Python
"""https://en.wikipedia.org/wiki/Rail_fence_cipher"""
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def encrypt(input_string: str, key: int) -> str:
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"""
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Shuffles the character of a string by placing each of them
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in a grid (the height is dependent on the key) in a zigzag
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formation and reading it left to right.
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>>> encrypt("Hello World", 4)
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'HWe olordll'
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>>> encrypt("This is a message", 0)
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Traceback (most recent call last):
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...
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ValueError: Height of grid can't be 0 or negative
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>>> encrypt(b"This is a byte string", 5)
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Traceback (most recent call last):
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...
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TypeError: sequence item 0: expected str instance, int found
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"""
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temp_grid: list[list[str]] = [[] for _ in range(key)]
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lowest = key - 1
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if key <= 0:
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raise ValueError("Height of grid can't be 0 or negative")
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if key == 1 or len(input_string) <= key:
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return input_string
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for position, character in enumerate(input_string):
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num = position % (lowest * 2) # puts it in bounds
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num = min(num, lowest * 2 - num) # creates zigzag pattern
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temp_grid[num].append(character)
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grid = ["".join(row) for row in temp_grid]
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output_string = "".join(grid)
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return output_string
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def decrypt(input_string: str, key: int) -> str:
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"""
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Generates a template based on the key and fills it in with
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the characters of the input string and then reading it in
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a zigzag formation.
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>>> decrypt("HWe olordll", 4)
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'Hello World'
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>>> decrypt("This is a message", -10)
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Traceback (most recent call last):
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...
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ValueError: Height of grid can't be 0 or negative
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>>> decrypt("My key is very big", 100)
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'My key is very big'
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"""
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grid = []
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lowest = key - 1
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if key <= 0:
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raise ValueError("Height of grid can't be 0 or negative")
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if key == 1:
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return input_string
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temp_grid: list[list[str]] = [[] for _ in range(key)] # generates template
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for position in range(len(input_string)):
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num = position % (lowest * 2) # puts it in bounds
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num = min(num, lowest * 2 - num) # creates zigzag pattern
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temp_grid[num].append("*")
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counter = 0
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for row in temp_grid: # fills in the characters
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splice = input_string[counter : counter + len(row)]
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grid.append(list(splice))
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counter += len(row)
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output_string = "" # reads as zigzag
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for position in range(len(input_string)):
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num = position % (lowest * 2) # puts it in bounds
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num = min(num, lowest * 2 - num) # creates zigzag pattern
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output_string += grid[num][0]
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grid[num].pop(0)
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return output_string
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def bruteforce(input_string: str) -> dict[int, str]:
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"""Uses decrypt function by guessing every key
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>>> bruteforce("HWe olordll")[4]
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'Hello World'
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"""
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results = {}
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for key_guess in range(1, len(input_string)): # tries every key
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results[key_guess] = decrypt(input_string, key_guess)
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return results
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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