Python凯撒密码暴力破解代码offset3=31时崩溃问题排查

Let's break down exactly what's going wrong in your code and fix it step by step:

1. Critical Logic Errors in option3 #

Your brute force function has two major flaws that cause crashes:

• The first condition if (ord(z) - offset3 < 126) is almost always true (even negative values are less than 126). This means you’re directly using invalid values like 32 - 31 = 1 (a non-printable control character) and eventually negative numbers (e.g., 32 - 94 = -62), which throw a ValueError when passed to chr() (since chr() only accepts values between 0 and 1114111).
• The second condition if (ord(z) - offset3 > 126) is impossible to trigger—ord(z) maxes out at 126, so subtracting any positive offset3 will never result in a value greater than 126. This branch never runs, so you never handle cases where the offset pushes characters below ASCII 32.

2. Similar Bug in option2 #

Your decryption function (option2) also has a reversed condition: if (ord(y) - offset > 126) will never be true. This means you never handle cases where subtracting the offset drops characters below ASCII 32, leading to the same crash risk for large offsets.

The Fix: Use Modulo Math for Reliable ASCII Wrapping #

Instead of fragile conditional checks, we can use modulo arithmetic to guarantee all character values stay within the ASCII 32-126 range (94 total characters). Here’s the foolproof formula:

1. Convert the character to a 0-93 range by subtracting 32
2. Apply the offset (add for encryption, subtract for decryption)
3. Use modulo 94 to wrap around the range
4. Convert back to 32-126 by adding 32

Corrected Full Code #

def get_menu_choice(): 
    print('\n*** Menu ***\n') 
    print('1. Encrypt string') 
    print('2. Decrypt string') 
    print('3. Brute force decryption') 
    print('4. Quit\n') 
    option = int(input('What would you like to do [1,2,3,4]?')) 
    while option not in [1, 2, 3, 4]: 
        option = int(input('Invalid choice, please enter either 1, 2, 3 or 4:')) 
    return option 

def get_offset(): 
    offset = int(input('Please enter offset value (1 to 94): ')) 
    # Add validation to ensure valid offset range
    while offset < 1 or offset > 94:
        offset = int(input('Invalid offset! Please enter a value between 1 and 94: '))
    return offset 

def option1(): 
    output1 = '' 
    encrypt = input('\nPlease enter string to encrypt: ') 
    offset = get_offset() 
    for x in encrypt:
        # Wrap character within ASCII 32-126
        adjusted = (ord(x) - 32 + offset) % 94
        output1 += chr(adjusted + 32)
    print('\nEncrypted string:\n', output1) 

def option2(): 
    output2 = '' 
    decrypt = input('\nPlease enter string to decrypt: ') 
    offset = get_offset() 
    for y in decrypt:
        # Wrap character within ASCII 32-126
        adjusted = (ord(y) - 32 - offset) % 94
        output2 += chr(adjusted + 32)
    print('\nDecrypted string:\n', output2) 

def option3(): 
    brutef = input('\nPlease enter string to decrypt: ') 
    print()
    for offset3 in range(0, 95): 
        output3 = ''
        for z in brutef:
            # Same reliable wrapping for brute force
            adjusted = (ord(z) - 32 - offset3) % 94
            output3 += chr(adjusted + 32)
        print(f'Offset: {offset3} = Decrypted string: {output3}') 

def option4(): 
    print('\nGoodbye!') 

run = 'y' 
while run == 'y': 
    option = get_menu_choice() 
    if option == 1: 
        option1() 
    elif option == 2: 
        option2() 
    elif option == 3: 
        option3() 
    elif option == 4: 
        option4() 
        run = 'n'

Key Improvements: #

• Replaced broken conditional checks with modulo math to keep characters within the required ASCII range
• Added offset validation to prevent invalid input
• Fixed typos (e.g., encrupt → encrypt)
• Cleaned up code structure for better readability
• Ensured brute force resets the output string correctly for each offset

Now your brute force decryption will run without crashing for any offset from 0 to 94, and all encryption/decryption operations will reliably wrap within the specified ASCII range.

内容的提问来源于stack exchange，提问作者Brendan Harris