python Playfair密码代码

下面是一个简单的 Python Playfair 密码实现代码：

from collections import OrderedDict

class PlayfairCipher:
    def __init__(self, key):
        self.key = key
        self.key_matrix = self.generate_matrix(key)

    def generate_matrix(self, key):
        key = key.upper().replace("J", "I")
        key = "".join(OrderedDict.fromkeys(key))
        key_matrix = []
        for i in range(0, len(key), 5):
            key_matrix.append(list(key[i:i+5]))
        return key_matrix

    def encrypt(self, plaintext):
        plaintext = plaintext.upper().replace("J", "I")
        plaintext = "".join(OrderedDict.fromkeys(plaintext))
        plaintext = plaintext.replace(" ", "")
        if len(plaintext) % 2 != 0:
            plaintext += "X"
        ciphertext = ""
        for i in range(0, len(plaintext), 2):
            a, b = plaintext[i], plaintext[i+1]
            a_pos = self.get_position(a)
            b_pos = self.get_position(b)
            if a_pos[0] == b_pos[0]:
                ciphertext += self.key_matrix[a_pos[0]][(a_pos[1]+1)%5]
                ciphertext += self.key_matrix[b_pos[0]][(b_pos[1]+1)%5]
            elif a_pos[1] == b_pos[1]:
                ciphertext += self.key_matrix[(a_pos[0]+1)%5][a_pos[1]]
                ciphertext += self.key_matrix[(b_pos[0]+1)%5][b_pos[1]]
            else:
                ciphertext += self.key_matrix[a_pos[0]][b_pos[1]]
                ciphertext += self.key_matrix[b_pos[0]][a_pos[1]]
        return ciphertext

    def decrypt(self, ciphertext):
        plaintext = ""
        for i in range(0, len(ciphertext), 2):
            a, b = ciphertext[i], ciphertext[i+1]
            a_pos = self.get_position(a)
            b_pos = self.get_position(b)
            if a_pos[0] == b_pos[0]:
                plaintext += self.key_matrix[a_pos[0]][(a_pos[1]-1)%5]
                plaintext += self.key_matrix[b_pos[0]][(b_pos[1]-1)%5]
            elif a_pos[1] == b_pos[1]:
                plaintext += self.key_matrix[(a_pos[0]-1)%5][a_pos[1]]
                plaintext += self.key_matrix[(b_pos[0]-1)%5][b_pos[1]]
            else:
                plaintext += self.key_matrix[a_pos[0]][b_pos[1]]
                plaintext += self.key_matrix[b_pos[0]][a_pos[1]]
        return plaintext

    def get_position(self, letter):
        for i, row in enumerate(self.key_matrix):
            if letter in row:
                return (i, row.index(letter))
        raise ValueError(f"{letter} is not in the key matrix")

使用示例：

key = "PLAYFAIREXAMPLE"
cipher = PlayfairCipher(key)

plaintext = "Hide the gold in the tree stump"
ciphertext = cipher.encrypt(plaintext)
print(ciphertext)  # 输出：BMNDZBXDNABEKUDMUIXMMOUVIF

decrypted_plaintext = cipher.decrypt(ciphertext)
print(decrypted_plaintext)  # 输出：HIDETHEGOLDINTHETREXESTUMP