如何解密加密代码中的文件？PNG加密图片解密技术咨询

Alright, let's walk through exactly how to decrypt your encrypted PNG following the rules you outlined. I'll break this down into clear steps with actionable code examples (using Python, since it's great for quick file manipulation):

Key Background First #

The core rules you mentioned translate to these critical details:

• XOR is reversible—if the original PNG byte was encrypted with byte XOR key, decrypting just requires doing the same XOR operation again. Since valid PNGs always start with 0x89, we can even derive the key if we don't have it upfront.
• We need to undo a position swap that was applied during encryption (common scenarios include reversing the entire file, swapping halves, or splitting into blocks).

Step 1: Get or Derive the Encryption Key #

If you already have the key, skip to Step 2. If not, calculate it using the first byte of the encrypted file:

# Read the first byte of your encrypted PNG
with open("encrypted.png", "rb") as enc_file:
    first_encrypted_byte = ord(enc_file.read(1))

# Derive the key using the standard PNG starting byte 0x89
key = 0x89 ^ first_encrypted_byte
print(f"Derived encryption key: 0x{key:02X}")

Step 2: Undo the Position Swap #

I'll use full byte reversal as a default example (adjust this if your swap rule is more specific, like swapping fixed-size blocks):

# Read the entire encrypted file content
with open("encrypted.png", "rb") as enc_file:
    encrypted_data = enc_file.read()

# Undo position swap (reverse the byte sequence here)
swapped_back_data = encrypted_data[::-1]

Step 3: Apply XOR Decryption #

Run the XOR operation with your key on every byte in the swapped-back data:

# XOR each byte with the key to decrypt
decrypted_data = bytes(byte ^ key for byte in swapped_back_data)

Step 4: Verify and Save the Decrypted PNG #

Save the result and check if it's a valid PNG (valid PNGs start with the byte sequence 0x89 0x50 0x4E 0x47 0x0D 0x0A 0x1A 0x0A):

# Save the decrypted file
with open("decrypted.png", "wb") as dec_file:
    dec_file.write(decrypted_data)

# Optional: Verify the header is correct
with open("decrypted.png", "rb") as dec_file:
    header = dec_file.read(8)
    if header == b'\x89PNG\r\n\x1a\n':
        print("Decryption successful! The PNG header is valid.")
    else:
        print("Warning: The decrypted file doesn't have a valid PNG header—check your position swap rule or key.")

Quick Notes #

• If the position swap isn't a full reversal, modify the swapped_back_data step to match the exact swap logic used during encryption.
• Always make a backup of your encrypted file before running decryption scripts!

内容的提问来源于stack exchange，提问作者KillerVibe