读取文件，给定密钥，打印出加密矩阵，将明文生成文件，实现 Playfair 密码的解密算法

很高兴为您解答问题。以下是实现 Playfair 密码的解密算法的代码：

def generate_matrix(key):
    # 生成加密矩阵
    matrix = []
    for c in key:
        if c not in matrix and c.isalpha():
            matrix.append(c)
    for c in "ABCDEFGHIKLMNOPQRSTUVWXYZ":
        if c not in matrix:
            matrix.append(c)
    return matrix

def encrypt(plaintext, key):
    # 加密明文
    matrix = generate_matrix(key)
    ciphertext = ""
    for i in range(0, len(plaintext), 2):
        if i == len(plaintext) - 1:
            plaintext += "X"
        if plaintext[i] == plaintext[i+1]:
            plaintext = plaintext[:i+1] + "X" + plaintext[i+1:]
        row1, col1 = divmod(matrix.index(plaintext[i]), 5)
        row2, col2 = divmod(matrix.index(plaintext[i+1]), 5)
        if row1 == row2:
            ciphertext += matrix[row1*5+(col1+1)%5]
            ciphertext += matrix[row2*5+(col2+1)%5]
        elif col1 == col2:
            ciphertext += matrix[((row1+1)%5)*5+col1]
            ciphertext += matrix[((row2+1)%5)*5+col2]
        else:
            ciphertext += matrix[row1*5+col2]
            ciphertext += matrix[row2*5+col1]
    return ciphertext

def decrypt(ciphertext, key):
    # 解密密文
    matrix = generate_matrix(key)
    plaintext = ""
    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:
            plaintext += matrix[row1*5+(col1-1)%5]
            plaintext += matrix[row2*5+(col2-1)%5]
        elif col1 == col2:
            plaintext += matrix[((row1-1)%5)*5+col1]
            plaintext += matrix[((row2-1)%5)*5+col2]
        else:
            plaintext += matrix[row1*5+col2]
            plaintext += matrix[row2*5+col1]
    return plaintext

# 读取文件
with open("plaintext.txt", "r") as f:
    plaintext = f.read().upper().replace("J", "I")

# 给定密钥
key = "PLAYFAIREXAMPLE"

# 打印出加密矩阵
matrix = generate_matrix(key)
for i in range(5):
    print(matrix[i*5:i*5+5])

# 将明文生成文件
with open("ciphertext.txt", "w") as f:
    f.write(encrypt(plaintext, key))

# 解密密文
with open("ciphertext.txt", "r") as f:
    ciphertext = f.read().upper()

plaintext = decrypt(ciphertext, key)
print(plaintext)

如果您有任何问题，请随时问我。