C#游戏数据加解密抛出Bad PKCS7 padding错误求助

我在实现游戏数据加解密功能时，解密阶段抛出了PKCS7填充错误，相关代码和错误信息如下：

加密函数 #

private void WriteEncryptedData<T>(T Data, string path)
{
    byte[] array;

    using (Aes aes = Aes.Create())  
    {  
        aes.Key = Convert.FromBase64String(KEY);
        aes.IV = Convert.FromBase64String(IV);
        aes.Padding = PaddingMode.PKCS7;

        ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);

        using MemoryStream memoryStream = new();
        using CryptoStream cryptoStream = new(memoryStream, encryptor, CryptoStreamMode.Write);
        cryptoStream.Write(Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(Data)));
        cryptoStream.FlushFinalBlock();
        array = memoryStream.ToArray();
    }
    
    File.WriteAllText(path, Convert.ToBase64String(array));
}

解密函数 #

private T ReadEncryptedData<T>(string path)
{
    var data = File.ReadAllText(path);
    byte[] array = Convert.FromBase64String(data);

    string result;

    using (Aes aes = Aes.Create())
    {
        aes.Key = Convert.FromBase64String(KEY);
        aes.IV = Convert.FromBase64String(IV);
        aes.Padding = PaddingMode.PKCS7;

        using ICryptoTransform cryptoTransform = aes.CreateDecryptor(aes.Key, aes.IV);
        using MemoryStream decryptionStream = new(array);
        using CryptoStream cryptoStream = new(
            decryptionStream,
            cryptoTransform,
            CryptoStreamMode.Read
        );
        
        cryptoStream.Flush();
        result = Encoding.UTF8.GetString(decryptionStream.ToArray());
    }

    Debug.Log($"Decrypted result (if the following is not legible, probably wrong key or iv): {result}");
    return JsonConvert.DeserializeObject<T>(result);
}

错误信息 #

加载数据失败，原因：Bad PKCS7 padding. Invalid length 0. at
Mono.Security.Cryptography.SymmetricTransform.ThrowBadPaddingException
(System.Security.Cryptography.PaddingMode padding, System.Int32
length, System.Int32 position) [0x00056] in
<381999f96ea944d79e461a81dcbea654>:0 at
Mono.Security.Cryptography.SymmetricTransform.FinalDecrypt
(System.Byte[] inputBuffer, System.Int32 inputOffset, System.Int32
inputCount) [0x00146] in <381999f96ea944d79e461a81dcbea654>:0 at
Mono.Security.Cryptography.SymmetricTransform.TransformFinalBlock
(System.Byte[] inputBuffer, System.Int32 inputOffset, System.Int32
inputCount) [0x0002e] in <381999f96ea944d79e461a81dcbea654>:0 at
System.Security.Cryptography.CryptoStream.FlushFinalBlock () [0x00013]
in <381999f96ea944d79e461a81dcbea654>:0 at
System.Security.Cryptography.CryptoStream.Dispose (System.Boolean
disposing) [0x0000b] in <381999f96ea944d79e461a81dcbea654>:0 at
System.IO.Stream.Close () [0x00000] in
<381999f96ea944d79e461a81dcbea654>:0 at System.IO.Stream.Dispose ()
[0x00000] in <381999f96ea944d79e461a81dcbea654>:0

问题根源与修复 #

核心问题 #

解密函数的错误在于直接读取底层decryptionStream的字节数组，跳过了CryptoStream的解密处理流程。CryptoStream需要完成加密数据的读取、解密、填充校验后，才能输出明文，直接访问原MemoryStream拿到的还是加密字节，导致填充校验失败。

修正后的解密函数 #

private T ReadEncryptedData<T>(string path)
{
    var data = File.ReadAllText(path);
    byte[] array = Convert.FromBase64String(data);

    string result;

    using (Aes aes = Aes.Create())
    {
        aes.Key = Convert.FromBase64String(KEY);
        aes.IV = Convert.FromBase64String(IV);
        aes.Padding = PaddingMode.PKCS7;

        using ICryptoTransform cryptoTransform = aes.CreateDecryptor(aes.Key, aes.IV);
        using MemoryStream decryptionStream = new(array);
        using CryptoStream cryptoStream = new(decryptionStream, cryptoTransform, CryptoStreamMode.Read);
        // 通过StreamReader读取CryptoStream处理后的明文
        using StreamReader reader = new(cryptoStream);
        result = reader.ReadToEnd();
    }

    Debug.Log($"Decrypted result: {result}");
    return JsonConvert.DeserializeObject<T>(result);
}

额外注意事项 #

1. 后续动态生成IV时，需将加密时使用的IV与加密数据一起存储（比如放在加密数据头部），解密时先读取IV再解密主体内容，确保解密用的IV和加密完全一致。
2. 确保KEY长度符合AES标准：AES-128对应16字节、AES-192对应24字节、AES-256对应32字节，Base64转换后的字符串长度需匹配对应字节数。

内容的提问来源于stack exchange，提问作者Ando