python aes解密去除pkcs7_padding

Python AES解密去除PKCS7 Padding

1. Introduction

AES (Advanced Encryption Standard) is a symmetric encryption algorithm widely used in securing data. When encrypting data with AES, a padding scheme like PKCS7 is often used to ensure that the data block size is a multiple of the block size of AES.

In this article, we will focus on decrypting AES-encrypted data and removing PKCS7 padding in Python.

2. AES Decryption with PyCryptodome

PyCryptodome is a Python library that provides cryptographic functions, including AES encryption and decryption. To decrypt AES-encrypted data with PyCryptodome, you need to specify the key and initialization vector (IV) used for encryption.

from Crypto.Cipher import AES
from Crypto.Util.Padding import unpad

def decrypt_aes(ciphertext, key, iv):
    cipher = AES.new(key, AES.MODE_CBC, iv)
    plaintext = cipher.decrypt(ciphertext)
    return plaintext

The decrypt_aes function takes the ciphertext, key, and IV as input and decrypts the ciphertext using AES in CBC mode.

3. Removing PKCS7 Padding

After decrypting the AES-encrypted data, you need to remove the PKCS7 padding to obtain the original plaintext. The PyCryptodome library provides the unpad function for this purpose.

def remove_pkcs7_padding(plaintext):
    unpadded = unpad(plaintext, AES.block_size)
    return unpadded

The remove_pkcs7_padding function takes the decrypted plaintext as input and removes the PKCS7 padding using the AES block size.

4. Putting It All Together

Now, let's decrypt an AES-encrypted message and remove the PKCS7 padding using the functions we defined earlier.

ciphertext = b'\xba5\xd7\xe3\xed\x0b\x1b\x82\xf0\xf3\xecv\xdb\x87\x9b\xed'
key = b'0123456789abcdef'
iv = b'\x00' * AES.block_size

decrypted = decrypt_aes(ciphertext, key, iv)
original_message = remove_pkcs7_padding(decrypted)

print(original_message.decode())

In this example, we decrypt the given ciphertext using the specified key and IV, and then remove the PKCS7 padding to obtain the original message.

5. Conclusion

In this article, we learned how to decrypt AES-encrypted data and remove PKCS7 padding in Python using the PyCryptodome library. By following the steps outlined in this article, you can easily decrypt AES-encrypted messages and retrieve the original plaintext.

Remember to handle encryption keys and IVs securely and ensure that the encryption and decryption processes are properly implemented to maintain data security.

---

journey
    title AES Decryption Journey

    section Decrypt AES
        participant Encryption
        participant Decryption
    end

    section Remove Padding
        participant Decryption
        participant Padding Removal
    end

    section Original Message
        participant Padding Removal
    end

classDiagram
    class AES
    class Padding
    class PyCryptodome
    AES <|-- PyCryptodome
    Padding <|-- PyCryptodome

By following the steps outlined in this article, you can easily decrypt AES-encrypted messages and retrieve the original plaintext. Remember to handle encryption keys and IVs securely and ensure that the encryption and decryption processes are properly implemented to maintain data security.