C#对RSA的密文进行分段解密，报参数错误

问题遇到的现象和发生背景

在对接银行系统接口时，使用RSA进行私钥分段解密，报参数错误

问题相关代码，请勿粘贴截图

public static string PrivateKeyDecrypt(string PrivateKey, string StrDecryptString)
 {
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            rsa.FromXmlString(PrivateKey);
            byte[] encryptData = Convert.FromBase64String(StrDecryptString);
            byte[] dencryContent;
            
            if (encryptData == null || encryptData.Length <= 0)
            {
                throw new NotSupportedException();
            }

            int keySize = rsa.KeySize / 8;
            byte[] buffer = new byte[keySize];

            MemoryStream input = new MemoryStream(encryptData);
            MemoryStream output = new MemoryStream();

            while (true)
            {
                int readLine = input.Read(buffer, 0, keySize);
                if (readLine <= 0)
                {
                    break;
                }
                byte[] temp = new byte[readLine];
                Array.Copy(buffer, 0, temp, 0, readLine);
                byte[] decrypt = rsa.Decrypt(temp, false);
                output.Write(decrypt, 0, decrypt.Length);
            }
            dencryContent = output.ToArray();

            return Encoding.UTF8.GetString(dencryContent);
 }

运行结果及报错内容

我想要达到的结果

有什么好的办法来处理这个问题吗？？