python实现经典密码学中列移位算法

Program: Columnar transposition (on alphabet string)

Reference：http://rumkin.com/tools/cipher/coltrans.php

A columnar transposition, also known as a row-column transpose, is a very simple cipher to perform by hand. First, you write your message in columns. Then, you just rearrange the columns. For example. I have the message, Which wristwatches are swiss wristwatches. You convert everything to upper case and write it without spaces. When you write it down, make sure to put it into columns and number them. Let’s use five columns.

	Unencoded	Rearranged
Column #:	4 2 5 3 1	1 2 3 4 5
	W H I C H	H H C W I
	W R I S T	T R S W I
	W A T C H	H A C W T
	E S A R E	E S R E A
	S W I S S	S W S S I
	W R I S T	T R S W I
	W A T C H	H A C W T
	E S	S E

Now, you just read the columns down in the order that you number them. Above, you will see the key is 4 2 5 3 1, which means you write down the last column first, then the second, then the fourth, the first, and finally the middle. When you are all done, you will get HTHESTHHRASWRASCSCRSSCWWWESWWEIITAIIT.

Your program does the following:

• Read an integer from the console, representing the column count. In the example above, the count is 5.
• Read the encryption key, i.e. the order of columns, separated by space. In the example above, the key is 4 2 5 3 1.
• Read the plaintext string in one line. In the example above, the plaintext is WHICHWRISTWATCHESARESWISSWRISTWATCHES.
• Perform the columnar transposition.
• Print the ciphertext string. In the example above, the ciphertext is HTHESTHHRASWRASCSCRSSCWWWESWWEIITAIIT.

Example Input & Output

Input:

代码语言：javascript复制

5
4 2 5 3 1
WHICHWRISTWATCHESARESWISSWRISTWATCHES

Output:

代码语言：javascript复制

HTHESTHHRASWRASCSCRSSCWWWESWWEIITAIIT

solution code

代码语言：javascript复制

import math

key = input('please enter the key：')


# 加密
def encryptMessage(msg):
    cipher = ""

    k_index = 0

    msg_len = float(len(msg))
    msg_lst = list(msg)
    key_lst = sorted(list(key))

    # 计算列数
    col = len(key)

    # 计算最大行
    row = int(math.ceil(msg_len / col))

    # 将空白处用'_'填充
    fill_null = int((row * col) - msg_len)
    msg_lst.extend('_' * fill_null)

    # 按行填充字符
    matrix = [msg_lst[i: i   col]
              for i in range(0, len(msg_lst), col)]

    # 重排顺序形成密文
    for _ in range(col):
        curr_idx = key.index(key_lst[k_index])
        cipher  = ''.join([row[curr_idx]
                           for row in matrix])
        k_index  = 1

    return cipher


# 解密过程
def decryptMessage(cipher):
    msg = ""

    k_index = 0

    msg_index = 0
    msg_len = float(len(cipher))
    msg_lst = list(cipher)

    # 计算列数
    col = len(key)

    # 求出最大行数
    row = int(math.ceil(msg_len / col))
    key_lst = sorted(list(key))

    # 创建新矩阵储存解密出的明文
    dec_cipher = []
    for _ in range(row):
        dec_cipher  = [[None] * col]

    # 按列重排矩阵
    for _ in range(col):
        curr_idx = key.index(key_lst[k_index])

        for j in range(row):
            dec_cipher[j][curr_idx] = msg_lst[msg_index]
            msg_index  = 1
        k_index  = 1

    # 转换为字符串输出
    try:
        msg = ''.join(sum(dec_cipher, []))
    except TypeError:
        raise TypeError("This program cannot",
                        "handle repeating words.")

    null_count = msg.count('_')

    if null_count > 0:
        return msg[: -null_count]

    return msg


msg = input('请输入加密的内容：')

cipher = encryptMessage(msg)
print("密文为: {}".
      format(cipher))

print("明文为: {}".
      format(decryptMessage(cipher)))

output

代码语言：javascript复制

please enter the key：42531
请输入加密的内容：WHICHWRISTWATCHESARESWISSWRISTWATCHES
密文为: HTHESTH_HRASWRASCSCRSSC_WWWESWWEIITAIIT_
明文为: WHICHWRISTWATCHESARESWISSWRISTWATCHES

进程已结束，退出代码为 0

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python实现经典密码学中列移位算法工程文件

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