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import itertools

import string

from typing import Generator, Iterable

def chunker(seq: Iterable[str], size: int) -> Generator[tuple[str, ...], None, None]:

it = iter(seq)

while True:

chunk = tuple(itertools.islice(it, size))

if not chunk:

return

yield chunk

def prepare_input(dirty: str) -> str:

"""

Prepare the plaintext by up-casing it

and separating repeated letters with X's

"""

dirty = "".join([c.upper() for c in dirty if c in string.ascii_letters])

clean = ""

if len(dirty) < 2:

return dirty

for i in range(len(dirty) - 1):

clean += dirty[i]

if dirty[i] == dirty[i + 1]:

clean += "X"

clean += dirty[-1]

if len(clean) & 1:

clean += "X"

return clean

def generate_table(key: str) -> list[str]:

# I and J are used interchangeably to allow

# us to use a 5x5 table (25 letters)

alphabet = "ABCDEFGHIKLMNOPQRSTUVWXYZ"

# we're using a list instead of a '2d' array because it makes the math

# for setting up the table and doing the actual encoding/decoding simpler

table = []

# copy key chars into the table if they are in `alphabet` ignoring duplicates

for char in key.upper():

if char not in table and char in alphabet:

table.append(char)

# fill the rest of the table in with the remaining alphabet chars

for char in alphabet:

if char not in table:

table.append(char)

return table

def encode(plaintext: str, key: str) -> str:

table = generate_table(key)

plaintext = prepare_input(plaintext)

ciphertext = ""

# https://en.wikipedia.org/wiki/Playfair_cipher#Description

for char1, char2 in chunker(plaintext, 2):

row1, col1 = divmod(table.index(char1), 5)

row2, col2 = divmod(table.index(char2), 5)

if row1 == row2:

ciphertext += table[row1 * 5 + (col1 + 1) % 5]

ciphertext += table[row2 * 5 + (col2 + 1) % 5]

elif col1 == col2:

ciphertext += table[((row1 + 1) % 5) * 5 + col1]

ciphertext += table[((row2 + 1) % 5) * 5 + col2]

else: # rectangle

ciphertext += table[row1 * 5 + col2]

ciphertext += table[row2 * 5 + col1]

return ciphertext

def decode(ciphertext: str, key: str) -> str:

table = generate_table(key)

plaintext = ""

# https://en.wikipedia.org/wiki/Playfair_cipher#Description

for char1, char2 in chunker(ciphertext, 2):

row1, col1 = divmod(table.index(char1), 5)

row2, col2 = divmod(table.index(char2), 5)

if row1 == row2:

plaintext += table[row1 * 5 + (col1 - 1) % 5]

plaintext += table[row2 * 5 + (col2 - 1) % 5]

elif col1 == col2:

plaintext += table[((row1 - 1) % 5) * 5 + col1]

plaintext += table[((row2 - 1) % 5) * 5 + col2]

else: # rectangle

plaintext += table[row1 * 5 + col2]

plaintext += table[row2 * 5 + col1]

return plaintext

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