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105 lines
2.8 KiB
Python
105 lines
2.8 KiB
Python
import itertools
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import string
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def chunker(seq, size):
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it = iter(seq)
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while True:
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chunk = tuple(itertools.islice(it, size))
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if not chunk:
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return
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yield chunk
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def prepare_input(dirty):
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"""
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Prepare the plaintext by up-casing it
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and separating repeated letters with X's
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"""
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dirty = "".join([c.upper() for c in dirty if c in string.ascii_letters])
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clean = ""
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if len(dirty) < 2:
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return dirty
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for i in range(len(dirty) - 1):
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clean += dirty[i]
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if dirty[i] == dirty[i + 1]:
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clean += "X"
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clean += dirty[-1]
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if len(clean) & 1:
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clean += "X"
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return clean
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def generate_table(key):
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# I and J are used interchangeably to allow
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# us to use a 5x5 table (25 letters)
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alphabet = "ABCDEFGHIKLMNOPQRSTUVWXYZ"
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# we're using a list instead of a '2d' array because it makes the math
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# for setting up the table and doing the actual encoding/decoding simpler
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table = []
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# copy key chars into the table if they are in `alphabet` ignoring duplicates
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for char in key.upper():
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if char not in table and char in alphabet:
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table.append(char)
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# fill the rest of the table in with the remaining alphabet chars
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for char in alphabet:
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if char not in table:
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table.append(char)
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return table
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def encode(plaintext, key):
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table = generate_table(key)
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plaintext = prepare_input(plaintext)
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ciphertext = ""
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# https://en.wikipedia.org/wiki/Playfair_cipher#Description
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for char1, char2 in chunker(plaintext, 2):
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row1, col1 = divmod(table.index(char1), 5)
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row2, col2 = divmod(table.index(char2), 5)
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if row1 == row2:
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ciphertext += table[row1 * 5 + (col1 + 1) % 5]
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ciphertext += table[row2 * 5 + (col2 + 1) % 5]
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elif col1 == col2:
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ciphertext += table[((row1 + 1) % 5) * 5 + col1]
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ciphertext += table[((row2 + 1) % 5) * 5 + col2]
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else: # rectangle
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ciphertext += table[row1 * 5 + col2]
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ciphertext += table[row2 * 5 + col1]
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return ciphertext
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def decode(ciphertext, key):
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table = generate_table(key)
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plaintext = ""
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# https://en.wikipedia.org/wiki/Playfair_cipher#Description
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for char1, char2 in chunker(ciphertext, 2):
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row1, col1 = divmod(table.index(char1), 5)
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row2, col2 = divmod(table.index(char2), 5)
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if row1 == row2:
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plaintext += table[row1 * 5 + (col1 - 1) % 5]
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plaintext += table[row2 * 5 + (col2 - 1) % 5]
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elif col1 == col2:
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plaintext += table[((row1 - 1) % 5) * 5 + col1]
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plaintext += table[((row2 - 1) % 5) * 5 + col2]
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else: # rectangle
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plaintext += table[row1 * 5 + col2]
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plaintext += table[row2 * 5 + col1]
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return plaintext
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