环境是 asp.net core 3.1  

目前我们接入了微信的发送代金券, 我们给用户发送了很多的代金券, 现在希望能收到用户消费代金券的回执信息, 所以这次接入核销事件回调通知

消费完代金券后收到微信推送过来的报文信息是

{
"id": "da6f347c-9160-56c8-9435-441919007f3a",
"create_time": "2020-04-28T21:11:36+08:00",
"resource_type": "encrypt-resource",
"event_type": "COUPON.USE",
"summary": "代金券核销通知",
"resource": {
"original_type": "coupon",
"algorithm": "AEAD_AES_256_GCM",
"ciphertext": "/////////这个还没有用到就报错了. 因此我就隐去了",
"associated_data": "coupon",
"nonce": "9xCooUyvImYw"
}
}

解密代码用的是腾讯官方的代码, 执行过程中报错了. 下面代码中写了注释的一行报错了

        private static string ALGORITHM = "AES/GCM/NoPadding";
        private static int TAG_LENGTH_BIT = 128;
        private static int NONCE_LENGTH_BYTE = 12;
        private static string AES_KEY = "Q9HBMJ2P0Z6N4F7V5DKUCAI8TSL3XE1YWGRO";


        public static string AesGcmDecrypt(string associatedData, string nonce, string ciphertext)
        {
            GcmBlockCipher gcmBlockCipher = new GcmBlockCipher(new AesEngine());
            AeadParameters aeadParameters = new AeadParameters(
                new KeyParameter(Encoding.UTF8.GetBytes(AES_KEY)),
                128,
                Encoding.UTF8.GetBytes(nonce),
                Encoding.UTF8.GetBytes(associatedData));
            gcmBlockCipher.Init(false, aeadParameters);//执行到这里就报错了, 见下面的错误信息

            byte[] data = Convert.FromBase64String(ciphertext);
            byte[] plaintext = new byte[gcmBlockCipher.GetOutputSize(data.Length)];
            int length = gcmBlockCipher.ProcessBytes(data, 0, data.Length, plaintext, 0);
            gcmBlockCipher.DoFinal(plaintext, length);
            return Encoding.UTF8.GetString(plaintext);
        }

d堆栈信息
发生异常: CLR/System.ArgumentException
“System.ArgumentException”类型的异常在 BouncyCastle.Crypto.dll 中发生，但未在用户代码中进行处理: 'Key length not 128/192/256 bits.'
   在 Org.BouncyCastle.Crypto.Engines.AesEngine.GenerateWorkingKey(Byte[] key, Boolean forEncryption)
   在 Org.BouncyCastle.Crypto.Engines.AesEngine.Init(Boolean forEncryption, ICipherParameters parameters)
   在 Org.BouncyCastle.Crypto.Modes.GcmBlockCipher.Init(Boolean forEncryption, ICipherParameters parameters)
   在 NSwagJson.WeiXinCashCouponApi.Utils.AesGcm.AesGcmDecrypt(String associatedData, String nonce, String ciphertext) 在 /Users/jianjl/code/nswagjson.weixincashcouponapi/NSwagJson.WeiXinCashCouponApi/Utils/AesGcm.cs 中: 第 32 行
   在 NSwagJson.WeiXinCashCouponApi.Controllers.CallBackController.CallBack(CouponCallBackRequest body) 在 /Users/jianjl/code/nswagjson.weixincashcouponapi/NSwagJson.WeiXinCashCouponApi/Controllers/CallBackController.cs 中: 第 80 行
   在 Microsoft.Extensions.Internal.ObjectMethodExecutor.Execute(Object target, Object[] parameters)
   在 Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.SyncActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeActionMethodAsync()
   在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeNextActionFilterAsync()