Flutter端AES CTR加密后Python端解密失败问题求助

问题背景 #

前端用Flutter的AES-CTR模式加密文本，后端Python解密失败。Flutter端加密正常，但Python端解密结果为乱码。

Flutter加密代码 #

final plainText =  "abcde";//encoded;
final key = enc.Key.fromUtf8('12345678901234567890123456789012');
final iv = enc.IV.fromUtf8('12345');
final encrypter = enc.Encrypter(enc.AES(key, mode: enc.AESMode.ctr, padding: null));

final encrypted = encrypter.encrypt(plainText, iv: iv);

print(encrypted.base64); // 输出: yJpzWuw=

原Python解密代码 #

print(text) # 输出: yJpzWuw=
plaintext = text.encode('utf-8')
key = '12345678901234567890123456789012'.encode("utf-8")
iv = '12345'.encode('utf-8')

iv_int = int.from_bytes(iv)
aes = pyaes.AESModeOfOperationCTR(key, pyaes.Counter(iv_int))
decrypted = aes.decrypt(plaintext)
print('Decrypted:', decrypted)

错误解密结果 #

Decrypted: b'\xe7:\xcb\x94\xbe\xbb\xf8\x1c'

解决方案 #

问题根源在于两处适配错误：

1. 未对Base64编码的密文做解码，直接用字符串编码后的字节解密
2. Flutter的IV.fromUtf8('12345')会自动将IV补全至16字节（用0x00填充），而原Python代码未做补全，且字节转整数时未指定大端序

修改后的Python解密代码：

import base64
import pyaes

ciphertext = base64.b64decode('yJpzWuw=')                       # 对Base64编码的密文解码
key = '12345678901234567890123456789012'.encode("utf-8")
iv = '12345\0\0\0\0\0\0\0\0\0\0\0'.encode('utf-8')              # 将IV补全为16字节，用0x00填充
iv_int = int.from_bytes(iv, 'big')                              # 按大端序将字节转为整数
aes = pyaes.AESModeOfOperationCTR(key, pyaes.Counter(iv_int))
decrypted = aes.decrypt(ciphertext)
print('Decrypted:', decrypted) 

内容的提问来源于stack exchange，提问作者Hansen