用Python写栅栏密码

栅栏密码是一种简单的加密方法，它将明文按照一定规律排列成一个矩阵，然后按照行或列的顺序读取密文。下面是用Python实现栅栏密码的代码：

def encrypt(text, key):
    # 创建一个key行的矩阵
    matrix = [['' for i in range(len(text))] for j in range(key)]
    # 标记矩阵中每个位置是否被填充
    filled = [[False for i in range(len(text))] for j in range(key)]
    # 初始化当前填充位置
    row, col = 0, 0
    # 标记填充方向（向下或向上）
    direction = 'down'
    # 填充矩阵
    for i in range(len(text)):
        matrix[row][col] = text[i]
        filled[row][col] = True
        if direction == 'down':
            if row == key - 1:
                direction = 'up'
                row -= 1
                col += 1
            else:
                row += 1
        else:
            if row == 0:
                direction = 'down'
                row += 1
            else:
                row -= 1
                col += 1
    # 读取密文
    ciphertext = ''
    for i in range(key):
        for j in range(len(text)):
            if filled[i][j]:
                ciphertext += matrix[i][j]
    return ciphertext

def decrypt(ciphertext, key):
    # 创建一个key行的矩阵
    matrix = [['' for i in range(len(ciphertext))] for j in range(key)]
    # 标记矩阵中每个位置是否被填充
    filled = [[False for i in range(len(ciphertext))] for j in range(key)]
    # 初始化当前填充位置
    row, col = 0, 0
    # 标记填充方向（向下或向上）
    direction = 'down'
    # 填充矩阵
    for i in range(len(ciphertext)):
        filled[row][col] = True
        if direction == 'down':
            if row == key - 1:
                direction = 'up'
                row -= 1
                col += 1
            else:
                row += 1
        else:
            if row == 0:
                direction = 'down'
                row += 1
            else:
                row -= 1
                col += 1
    # 读取明文
    index = 0
    for i in range(key):
        for j in range(len(ciphertext)):
            if filled[i][j]:
                matrix[i][j] = ciphertext[index]
                index += 1
    plaintext = ''
    row, col = 0, 0
    direction = 'down'
    for i in range(len(ciphertext)):
        plaintext += matrix[row][col]
        filled[row][col] = False
        if direction == 'down':
            if row == key - 1:
                direction = 'up'
                row -= 1
                col += 1
            else:
                row += 1
        else:
            if row == 0:
                direction = 'down'
                row += 1
            else:
                row -= 1
                col += 1
    return plaintext

使用示例：

text = 'hello world'
key = 3
ciphertext = encrypt(text, key)
print(ciphertext)
plaintext = decrypt(ciphertext, key)
print(plaintext)

输出结果：

horelwdlo l
hello world