Python檔案加密換位加密法實作

# transposition_cipher.py
def encrypt_message(key, message):
    # 將訊息轉換為列表以便操作
    message_list = list(message)
    # 根據金鑰進行換位加密
    encrypted_message = [''] * key
    for col in range(key):
        pointer = col
        while pointer < len(message):
            encrypted_message[col] += message_list[pointer]
            pointer += key
    return ''.join(encrypted_message)

def decrypt_message(key, message):
    # 計算解密所需的列數
    num_cols = math.ceil(len(message) / key)
    num_rows = key
    num_shaded_boxes = (num_cols * num_rows) - len(message)
    # 初始化解密後的訊息列表
    decrypted_message = [''] * num_cols
    col = 0
    row = 0
    for symbol in message:
        decrypted_message[col] += symbol
        col += 1
        if (col == num_cols) or (col == num_cols - 1 and row >= num_rows - num_shaded_boxes):
            col = 0
            row += 1
    return ''.join(decrypted_message)

#### 程式碼解析
# 1. `encrypt_message`函式透過重新排列明文字元來實作加密。
# 2. `decrypt_message`函式根據相同的金鑰重新排列密鑰字元以還原明文。
# 3. 程式碼中使用了列表操作和數學計算來實作加密和解密邏輯。

# file_encryption.py
import os
import transposition_cipher

def main():
 filename = input("請輸入要加密/解密的檔案名稱：")
 mode = input("請選擇操作模式 (E)ncrypt/(D)ecrypt：")
 key = int(input("請輸入金鑰："))

 if not os.path.exists(filename):
 print(f"{filename} 檔案不存在！")
 return

 with open(filename, 'r', encoding='utf-8') as file:
 content = file.read()

 if mode.upper() == 'E':
 result = transposition_cipher.encrypt_message(key, content)
 output_filename = f"{filename}.encrypted"
 else:
 result = transposition_cipher.decrypt_message(key, content)
 output_filename = f"{filename}.decrypted"

 with open(output_filename, 'w', encoding='utf-8') as output_file:
 output_file.write(result)

 print(f"操作完成！結果已儲存到 {output_filename}")

#### 程式碼解析
# 1. 程式首先檢查輸入檔案是否存在。
# 2. 根據使用者選擇的模式，對檔案內容進行加密或解密。
# 3. 將處理後的結果寫入新的檔案中。
# 4. 程式中使用了`with`陳述式來自動管理檔案的開啟和關閉。

# 換位加密檔案處理實作
import time
import os
import sys

def encrypt_message(key, message):
    """
    換位加密核心演算法實作
    """
    # 將明文分段處理
    ciphertext = [''] * key
    for col in range(key):
        pointer = col
        while pointer < len(message):
            ciphertext[col] += message[pointer]
            pointer += key
    return ''.join(ciphertext)

def decrypt_message(key, ciphertext):
    """
    換位解密核心演算法實作
    """
    # 計算欄位數量
    num_cols = key
    num_rows = (len(ciphertext) // num_cols) + 1
    num_empty_cells = (num_cols * num_rows) - len(ciphertext)
    
    plaintext = [''] * num_rows
    col = 0
    row = 0
    
    for symbol in ciphertext:
        plaintext[row] += symbol
        row += 1
        if row == num_rows - num_empty_cells or (row == num_rows and col <= num_empty_cells - 1):
            row = 0
            col += 1
    
    return ''.join(plaintext)

def main():
    input_filename = 'example.txt'
    output_filename = 'example.encrypted.txt'
    key = 10
    mode = 'encrypt'  # 可選擇 'encrypt' 或 'decrypt'

    # 檢查輸入檔案是否存在
    if not os.path.exists(input_filename):
        print(f'錯誤：檔案 {input_filename} 不存在。')
        sys.exit()

    # 檢查輸出檔案是否已存在
    if os.path.exists(output_filename):
        print(f'警告：檔案 {output_filename} 已存在，是否覆寫？(Y/N)')
        response = input('> ').lower()
        if response != 'y':
            sys.exit()

    # 讀取輸入檔案內容
    with open(input_filename, 'r', encoding='utf-8') as file_obj:
        content = file_obj.read()

    # 記錄處理時間
    start_time = time.time()
    if mode == 'encrypt':
        result = encrypt_message(key, content)
    else:
        result = decrypt_message(key, content)
    total_time = round(time.time() - start_time, 2)

    # 寫入輸出檔案
    with open(output_filename, 'w', encoding='utf-8') as output_file:
        output_file.write(result)

    print(f'{mode.title()}ion 完成，耗時：{total_time} 秒')
    print(f'處理後檔案儲存為：{output_filename}')

if __name__ == '__main__':
    main()