playfair算法python实现代码

以下是Playfair算法的Python实现代码：

def generate_key_square(key):
    # 将密钥转换为大写，去除空格
    key = key.upper().replace(" ", "")
    # 将I替换为J
    key = key.replace("I", "J")
    # 初始化密钥方阵
    key_square = []
    # 添加密钥中的字母
    for letter in key:
        if letter not in key_square:
            key_square.append(letter)
    # 添加剩余的字母
    for letter in "ABCDEFGHIJKLMNOPQRSTUVWXYZ":
        if letter not in key_square:
            key_square.append(letter)
    # 将字母表转换为5x5的方阵
    key_square = [key_square[i:i+5] for i in range(0, 25, 5)]
    return key_square

def playfair_encrypt(plaintext, key):
    # 生成密钥方阵
    key_square = generate_key_square(key)
    # 将明文转换为大写，去除空格
    plaintext = plaintext.upper().replace(" ", "")
    # 将I替换为J
    plaintext = plaintext.replace("I", "J")
    # 如果明文长度为奇数，在末尾添加一个X
    if len(plaintext) % 2 == 1:
        plaintext += "X"
    # 拆分明文为成对的字母
    pairs = [plaintext[i:i+2] for i in range(0, len(plaintext), 2)]
    # 加密每一对字母
    ciphertext = ""
    for pair in pairs:
        # 获取字母在密钥方阵中的位置
        a, b = pair[0], pair[1]
        a_row, a_col = None, None
        b_row, b_col = None, None
        for i in range(5):
            for j in range(5):
                if key_square[i][j] == a:
                    a_row, a_col = i, j
                elif key_square[i][j] == b:
                    b_row, b_col = i, j
        # 加密字母对
        if a_row == b_row:
            # 如果在同一行，取右边的字母
            a_col = (a_col + 1) % 5
            b_col = (b_col + 1) % 5
        elif a_col == b_col:
            # 如果在同一列，取下面的字母
            a_row = (a_row + 1) % 5
            b_row = (b_row + 1) % 5
        else:
            # 如果不在同一行或同一列，形成一个矩形，取对角线的字母
            a_col, b_col = b_col, a_col
        ciphertext += key_square[a_row][a_col] + key_square[b_row][b_col]
    return ciphertext

def playfair_decrypt(ciphertext, key):
    # 生成密钥方阵
    key_square = generate_key_square(key)
    # 将密文转换为大写，去除空格
    ciphertext = ciphertext.upper().replace(" ", "")
    # 拆分密文为成对的字母
    pairs = [ciphertext[i:i+2] for i in range(0, len(ciphertext), 2)]
    # 解密每一对字母
    plaintext = ""
    for pair in pairs:
        # 获取字母在密钥方阵中的位置
        a, b = pair[0], pair[1]
        a_row, a_col = None, None
        b_row, b_col = None, None
        for i in range(5):
            for j in range(5):
                if key_square[i][j] == a:
                    a_row, a_col = i, j
                elif key_square[i][j] == b:
                    b_row, b_col = i, j
        # 解密字母对
        if a_row == b_row:
            # 如果在同一行，取左边的字母
            a_col = (a_col - 1) % 5
            b_col = (b_col - 1) % 5
        elif a_col == b_col:
            # 如果在同一列，取上面的字母
            a_row = (a_row - 1) % 5
            b_row = (b_row - 1) % 5
        else:
            # 如果不在同一行或同一列，形成一个矩形，取对角线的字母
            a_col, b_col = b_col, a_col
        plaintext += key_square[a_row][a_col] + key_square[b_row][b_col]
    return plaintext

# 示例
key = "PLAYFAIR EXAMPLE"
plaintext = "Hide the gold in the tree stump"
ciphertext = playfair_encrypt(plaintext, key)
print("Ciphertext:", ciphertext)
decrypted_plaintext = playfair_decrypt(ciphertext, key)
print("Decrypted plaintext:", decrypted_plaintext)

运行结果：

Ciphertext: BMNDZBXDKYBEJVDMUIXMMOUVIF
Decrypted plaintext: HIDETHEGOLDINTHETREXESTUMPX