playfair python加密和解密

以下是 Python 实现的 Playfair 加密和解密：

加密：

def playfair_encrypt(key, plaintext):
    # 将明文中的 J 替换为 I
    plaintext = plaintext.replace("J", "I")
    
    # 构造 Playfair 方阵
    matrix = []
    chars = list(key.upper()) + [chr(i) for i in range(65, 91) if chr(i) != "J" and chr(i) not in key.upper()]
    for i in range(0, 25, 5):
        matrix.append(chars[i:i+5])
    
    # 将明文分块
    plaintext_blocks = []
    i = 0
    while i < len(plaintext):
        if i == len(plaintext) - 1 or plaintext[i] == plaintext[i+1]:
            plaintext_blocks.append(plaintext[i] + "X")
            i += 1
        else:
            plaintext_blocks.append(plaintext[i:i+2])
            i += 2
    
    # 加密每个明文块
    ciphertext_blocks = []
    for block in plaintext_blocks:
        row1, col1 = divmod(matrix.index(block[0]), 5)
        row2, col2 = divmod(matrix.index(block[1]), 5)
        
        if row1 == row2:
            # 同一行
            ciphertext_blocks.append(matrix[row1][(col1 + 1) % 5] + matrix[row2][(col2 + 1) % 5])
        elif col1 == col2:
            # 同一列
            ciphertext_blocks.append(matrix[(row1 + 1) % 5][col1] + matrix[(row2 + 1) % 5][col2])
        else:
            # 不同行不同列
            ciphertext_blocks.append(matrix[row1][col2] + matrix[row2][col1])
    
    # 将密文块拼接成密文
    ciphertext = "".join(ciphertext_blocks)
    return ciphertext

解密：

def playfair_decrypt(key, ciphertext):
    # 构造 Playfair 方阵
    matrix = []
    chars = list(key.upper()) + [chr(i) for i in range(65, 91) if chr(i) != "J" and chr(i) not in key.upper()]
    for i in range(0, 25, 5):
        matrix.append(chars[i:i+5])
    
    # 解密每个密文块
    plaintext_blocks = []
    for i in range(0, len(ciphertext), 2):
        row1, col1 = divmod(matrix.index(ciphertext[i]), 5)
        row2, col2 = divmod(matrix.index(ciphertext[i+1]), 5)
        
        if row1 == row2:
            # 同一行
            plaintext_blocks.append(matrix[row1][(col1 - 1) % 5] + matrix[row2][(col2 - 1) % 5])
        elif col1 == col2:
            # 同一列
            plaintext_blocks.append(matrix[(row1 - 1) % 5][col1] + matrix[(row2 - 1) % 5][col2])
        else:
            # 不同行不同列
            plaintext_blocks.append(matrix[row1][col2] + matrix[row2][col1])
    
    # 将明文块拼接成明文
    plaintext = "".join(plaintext_blocks)
    
    # 将明文中的 X 替换为原来的字母
    plaintext = plaintext.replace("X", "")
    
    return plaintext

使用示例：

key = "playfair example"
plaintext = "Hide the gold in the tree stump"
ciphertext = playfair_encrypt(key, plaintext)
print(ciphertext)

# 输出：BMNDZBXDNABEKUDMUIXMMOUVIF

key = "playfair example"
ciphertext = "BMNDZBXDNABEKUDMUIXMMOUVIF"
plaintext = playfair_decrypt(key, ciphertext)
print(plaintext)

# 输出：HIDETHEGOLDINTHETREXESTUMP