Mitigating RsaCryptoServiceProvider thread safety issues on a web server

I have an X509Certificate2 instance, and obtain its PrivateKey property, which is an RsaCryptoServiceProvider. MSDN documents that this RsaCryptoServiceProvider class is not thread-safe. So if given some X.509 cert I need to perform asymmetric encryption on multiple threads (typical on a web server), what is the best way to create multiple instances of the RsaCryptoServiceProvider?

The private key 开发者_如何学Goon the X509Certificate2 is not marked as exportable, so I cannot simply export parameters on the original RsaCryptoServiceProvider and re-import them into another instance in order to workaround the thread-safety issues.

I obtained the original via the X509Store, but that seems to be a collection of X509Certificate2 instances such that if I want a new instance of RsaCryptoServiceProvider I have to instantiate a new X509Store to find a new X509Certificate2, to obtain a new RsaCryptoServiceProvider. It just seems awfully heavyweight to just getting .NET to clone the RsaCryptoServiceProvider instance.

Are there any better ways?

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It would seem that RsaCryptoServiceProvider, despite its MSDN documentation stating it is not thread-safe, is thread-safe enough to encrypt/decrypt on multiple threads at once. I wrote the following app to test high concurrency using this class, and it hasn't crashed or failed to encrypt/decrypt correctly at all:

using System;
using System.Diagnostics;
using System.Linq;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using System.Threading;

namespace ConsoleApplication1 {
    class Program {
        static bool exit;

        static void Main(string[] args) {
            var store = new X509Store(StoreName.My, StoreLocation.CurrentUser);
            try {
                store.Open(OpenFlags.OpenExistingOnly);

                Func<RSACryptoServiceProvider> rsaFactory = null;
                X509Certificate2 winningCert = null;
                exit = true;
                foreach (X509Certificate2 cert in store.Certificates) {
                    try {
                        var result = store.Certificates.Find(X509FindType.FindByThumbprint, cert.Thumbprint, false).Cast<X509Certificate2>().FirstOrDefault();
                        rsaFactory = () => (RSACryptoServiceProvider)result.PrivateKey;
                        UseRsa(rsaFactory());
                        winningCert = cert;
                        break;
                    } catch (CryptographicException) {
                        Console.WriteLine("Cert {0} failed", cert.Thumbprint);
                    }
                }

                exit = false;
                Console.WriteLine("Winning cert: {0}", winningCert.Thumbprint);
                RSACryptoServiceProvider rsa = (RSACryptoServiceProvider)winningCert.PrivateKey;
                rsaFactory = () => rsa;
                Thread[] threads = new Thread[16];
                for (int i = 0; i < threads.Length; i++) {
                    threads[i] = new Thread(state => UseRsa(rsaFactory()));
                    threads[i].Start();
                }

                Thread.Sleep(10000);

                exit = true;
                for (int i = 0; i < threads.Length; i++) {
                    threads[i].Join();
                }

                Console.WriteLine("Success.");
            } finally {
                store.Close();
            }
        }

        static void UseRsa(RSACryptoServiceProvider rsa) {
            var rng = RandomNumberGenerator.Create();
            var buffer = new byte[64];

            do {
                rng.GetBytes(buffer);
                var cipher = rsa.Encrypt(buffer, true);

                var plaintext = rsa.Decrypt(cipher, true);
                for (int i = 0; i < buffer.Length; i++) {
                    if (buffer[i] != plaintext[i]) {
                        Debugger.Break();
                    }
                }
            } while (!exit);
        }
    }
}