Function decode

ciphers/playfair_cipher.py:121–150

Decode the input string using the provided key. >>> decode("BMZFAZRZDH", "HAZARD") 'FIREHAZARD' >>> decode("HNBWBPQT", "AUTOMOBILE") 'DRIVINGX' >>> decode("SLYSSAQS", "CASTLE") 'ATXTACKX'

(ciphertext: str, key: str)

def decode(ciphertext: str, key: str) -> str:
    """
    Decode the input string using the provided key.

    >>> decode("BMZFAZRZDH", "HAZARD")
    'FIREHAZARD'
    >>> decode("HNBWBPQT", "AUTOMOBILE")
    'DRIVINGX'
    >>> decode("SLYSSAQS", "CASTLE")
    'ATXTACKX'
    """

    table = generate_table(key)
    plaintext = ""

    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


if __name__ == "__main__":