置換加密演算法

加密

Common sense is not so common.

Cenoonommstmme oo snnio s s c

# !python3.3

def TranspositionCipher(key, message):
    """
    @param key: a positive number used for encryption
    @param message: the plain text needs encryption
    @return: the encrypted text
    """
    if key <= 0: # the algorithm can't work
        return message 
    else:
        return "".join([message[i::key] for i in range(key)])
 

解密

Cenoonommstmme oo snnio s s c

30/8 = 3.75

Common sense is not so common.

def DecryptTranspositionCipher(key, message):
    """
    @param key: a positive number used for encryption
    @param message:  the encrypted message
    @return: plaintext
    """
    import math
    numOfColumns = math.ceil(len(message) / key)
    numOfRows = key
    numOfShadeBoxes = (numOfColumns * numOfRows) - len(message)
    plaintext = [''] * numOfColumns
    
    col = 0
    row = 0
    for symbol in message:
        plaintext[col] += symbol
        col += 1

        if (col == numOfColumns) or (col == numOfColumns-1 and row>=numOfRows-numOfShadeBoxes):
            col = 0
            row += 1
    return ''.join(plaintext)