Python AES256解密异常排查：跨Java微服务解密不一致问题

在Python与Java跨微服务AES256加密通信实验中，出现Python端解密函数无法正确解密数据，但Java服务可正常解密同一加密内容的问题。以下是问题代码、分析及修复方案：

原Python加密解密代码 #

import base64

from Crypto.Cipher import AES
from Crypto.Hash import SHA512
from Crypto.Random import get_random_bytes
import secrets
import random
import string
from Crypto.Util import Counter


def generateKey():
    key = base64.b64encode(secrets.token_bytes(16))
    iv = secrets.token_bytes(16)
    return key.decode("utf-8"), iv


def encryptAES(key, iv, raw):
    raw_2 = raw.encode("utf-8")
    cipher = AES.new(key.encode("utf-8"), AES.MODE_CFB, iv, segment_size=128)
    encrypted = base64.b64encode(iv + cipher.encrypt(raw_2))
    return encrypted.decode("utf-8")


def decryptAES(msg, key):
    raw_2 = msg.encode("ascii")
    iv = raw_2[:16]
    cipher = AES.new(key.encode("utf-8"), AES.MODE_CFB, iv, segment_size=128)
    cipher_decrypt = cipher.decrypt(raw_2[16:])
    cipher_decrypt_b64 = base64.b64encode(cipher_decrypt)
    return cipher_decrypt_b64.decode("utf-8")


initial_data = "Empty string"
keys = generateKey()
encrypted_data = encryptAES(keys[0], keys[1], initial_data)
print(encrypted_data)
print(decryptAES(msg=encrypted_data, key=keys[0]))

Java解密代码 #

public String decrypt(String encrypted_encoded_string, String KEY){

    String plain_text = "";
    try{
        byte[] encrypted_decoded_bytes = Base64.getDecoder().decode(encrypted_encoded_string);
        String encrypted_decoded_string = new String(encrypted_decoded_bytes);
        String iv_string = encrypted_decoded_string.substring(0,16); //IV is retrieved correctly.

        IvParameterSpec iv = new IvParameterSpec(Arrays.copyOf(encrypted_decoded_bytes, 16));
        SecretKeySpec skeySpec = new SecretKeySpec(KEY.getBytes("UTF-8"), "AES");

        Cipher cipher = Cipher.getInstance("AES/CFB/NoPadding");
        cipher.init(Cipher.DECRYPT_MODE, skeySpec, iv);

        plain_text = new String(cipher.doFinal(Arrays.copyOfRange(encrypted_decoded_bytes, 16, encrypted_decoded_bytes.length)));//Returns garbage characters
        return plain_text;

    }  catch (Exception e) {
        Log.i(TAG, e.getMessage());
    }
    return plain_text;
}

问题核心分析 #

原Python解密函数存在两处逻辑错误：

1. Base64处理顺序颠倒：加密流程是「拼接IV+密文二进制 → Base64编码」，但原解密直接将加密字符串转ASCII字节，未先做Base64解码，导致IV和密文都是Base64编码后的字节，而非原始二进制数据。
2. 多余的Base64编码：解密得到明文字节后，无需再次进行Base64编码，原代码错误地将明文重新编码返回，导致输出不是原始明文。

修正后的Python解密函数 #

def decryptAES(msg, key):
    raw_2 = base64.b64decode(msg)  # 先解码Base64，还原IV+密文的原始二进制数据

    iv = raw_2[:16]
    cipher = AES.new(key.encode("utf-8"), AES.MODE_CFB, iv, segment_size=128)
    cipher_decrypt = cipher.decrypt(raw_2[16:])  # 解密后直接得到明文字节
    return cipher_decrypt.decode("utf-8")  # 转成UTF-8字符串返回原始明文

内容的提问来源于stack exchange，提问作者Piotr Dymała