如何在C#中编程创建带不可导出私钥的Windows密钥库X509证书

我希望在C#中创建私钥并添加证书（自签名或CA签发），仅允许导出证书，同时将私钥设置为不可导出——即通过certmgr（证书管理器）导出证书时，“是，导出私钥”选项会被禁用。通常通过Crypto Shell Extensions安装.pfx/.p12文件时，取消勾选“标记此密钥为可导出”即可实现私钥不可导出。

我已成功创建密钥对并将证书条目添加到Windows密钥库，但“是，导出私钥”选项始终处于启用状态，无法限制私钥导出。尝试的代码如下：

public void init(){
    AsymmetricCipherKeyPair asymmetricCipherKeyPair = GetKeyPair();

    X509Name issuer = this.GenerateRelativeDistinguishedName("test org");
    X509Name subject = this.GenerateRelativeDistinguishedName("test user1");


    Org.BouncyCastle.X509.X509Certificate cert = GenerateCertificate(issuer, subject, asymmetricCipherKeyPair.Private, asymmetricCipherKeyPair.Public);
    importSelfSignedCert(asymmetricCipherKeyPair, cert);
}

private AsymmetricCipherKeyPair GetKeyPair()
{
    return new Pkcs1xHandler().GenerateKeyPair(Constants.RsaKeyLength.Length2048Bits);
}
 
protected X509Name GenerateRelativeDistinguishedName(String commonName)
{
    IDictionary attributes = new Hashtable();
    IList ordering;

    attributes.Add(X509Name.CN, commonName);

    ordering = new ArrayList(attributes.Keys);
    return new X509Name(ordering, attributes);
}


protected void importSelfSignedCert(AsymmetricCipherKeyPair asymmetricCipherKeyPair, Org.BouncyCastle.X509.X509Certificate cert)
{
    try
    {
        int ID =1;
        AsymmetricCipherKeyPair ackp = asymmetricCipherKeyPair;
        var rsaPriv = Org.BouncyCastle.Security.DotNetUtilities.ToRSA(ackp.Private as RsaPrivateCrtKeyParameters);

        // Setup RSACryptoServiceProvider with "KeyContainerName" set to "KeyContainer"+ enrollmentID
        var csp = new CspParameters();
        csp.KeyContainerName = "TestPrivKey" + ID;
        csp.Flags |= CspProviderFlags.UseMachineKeyStore;

        var rsaPrivate = new RSACryptoServiceProvider(csp);

        // Import private key to windows keystrore, from already generated BouncyCastle rsa privatekey
        rsaPrivate.ImportParameters(rsaPriv.ExportParameters(true));
        //Console.Write("rsaprivate key:" + rsaPrivate.ToXmlString(true));

        System.Security.Cryptography.X509Certificates.X509Certificate2 certificate = new System.Security.Cryptography.X509Certificates.X509Certificate2();
        var flags = X509KeyStorageFlags.MachineKeySet | X509KeyStorageFlags.PersistKeySet | X509KeyStorageFlags.UserKeySet;
        certificate.Import(cert.GetEncoded(), String.Empty, flags);
        certificate.PrivateKey = rsaPrivate;


        // opening up the windows cert store because thats where I want to save it.
        System.Security.Cryptography.X509Certificates.X509Store store = new System.Security.Cryptography.X509Certificates.X509Store(System.Security.Cryptography.X509Certificates.StoreName.My, System.Security.Cryptography.X509Certificates.StoreLocation.CurrentUser);
        store.Open(System.Security.Cryptography.X509Certificates.OpenFlags.MaxAllowed);
        store.Add(certificate);
        store.Close();

        rsaPrivate.PersistKeyInCsp = true; //persisting the key in container is important to retrieve the key later


        ///make non exporable
        csp.Flags = CspProviderFlags.UseNonExportableKey;
        var rsaPrivate2 = new RSACryptoServiceProvider(csp);
        rsaPrivate2.ExportParameters(false); //restrict to export
        rsaPrivate2.PersistKeyInCsp = true;
    }
    catch (Exception e)
    {
        System.Diagnostics.Debug.WriteLine("Error : " + e);
        Console.WriteLine(e);
        Log.Print(LogLevel.High, e.ToString());
    }
}

请问如何在编程创建时实现私钥不可导出？

你的代码核心问题在于私钥容器创建时没有设置不可导出标记，后续修改CspParameters再创建新的RSACryptoServiceProvider不会改变已存在的密钥容器属性。要实现私钥不可导出，必须在首次创建/导入私钥到容器时就指定UseNonExportableKey标记。

关键修正点 #

• 初始化CspParameters时就添加CspProviderFlags.UseNonExportableKey，确保密钥容器从创建起就标记为不可导出。
• 避免混合使用MachineKeySet和UserKeySet，两者互斥，根据实际存储位置选择其一。
• 无需后续创建第二个RSACryptoServiceProvider实例，首次导入时就完成不可导出设置。

修正后的importSelfSignedCert方法 #

protected void importSelfSignedCert(AsymmetricCipherKeyPair asymmetricCipherKeyPair, Org.BouncyCastle.X509.X509Certificate cert)
{
    try
    {
        int ID = 1;
        var rsaPriv = Org.BouncyCastle.Security.DotNetUtilities.ToRSA(asymmetricCipherKeyPair.Private as RsaPrivateCrtKeyParameters);

        // 初始化CspParameters时直接设置不可导出标记，选择存储位置（这里用CurrentUser，若需机器级则用UseMachineKeyStore）
        var csp = new CspParameters();
        csp.KeyContainerName = "TestPrivKey" + ID;
        // 关键：添加UseNonExportableKey标记，确保私钥不可导出
        csp.Flags = CspProviderFlags.UseNonExportableKey | CspProviderFlags.UseUserKeyStore;

        // 创建RSACryptoServiceProvider，此时容器已标记为不可导出
        var rsaPrivate = new RSACryptoServiceProvider(csp);
        rsaPrivate.ImportParameters(rsaPriv.ExportParameters(true));
        rsaPrivate.PersistKeyInCsp = true;

        // 转换BouncyCastle证书为.NET X509Certificate2
        byte[] certBytes = cert.GetEncoded();
        var certificate = new System.Security.Cryptography.X509Certificates.X509Certificate2(
            certBytes, 
            string.Empty, 
            // 匹配密钥存储位置，避免冲突
            X509KeyStorageFlags.PersistKeySet | X509KeyStorageFlags.UserKeySet
        );

        // 关联私钥到证书（推荐使用CopyWithPrivateKey替代直接赋值PrivateKey）
        certificate = certificate.CopyWithPrivateKey(rsaPrivate);

        // 将证书添加到系统存储
        using (var store = new System.Security.Cryptography.X509Certificates.X509Store(
            System.Security.Cryptography.X509Certificates.StoreName.My, 
            System.Security.Cryptography.X509Certificates.StoreLocation.CurrentUser))
        {
            store.Open(System.Security.Cryptography.X509Certificates.OpenFlags.ReadWrite);
            store.Add(certificate);
        }
    }
    catch (Exception e)
    {
        System.Diagnostics.Debug.WriteLine("Error : " + e);
        Console.WriteLine(e);
        Log.Print(LogLevel.High, e.ToString());
    }
}

额外说明 #

• 使用CopyWithPrivateKey替代直接赋值PrivateKey，这是.NET推荐的更安全的关联方式，避免潜在的兼容性问题。
• 若需要将证书存储到机器级（所有用户可见），则将CspProviderFlags.UseUserKeyStore改为CspProviderFlags.UseMachineKeyStore，同时X509KeyStorageFlags对应改为MachineKeySet，存储位置改为StoreLocation.LocalMachine。
• 密钥容器一旦创建并标记为不可导出，无法再修改其导出属性，必须删除容器重新创建才能变更。

内容的提问来源于stack exchange，提问作者sharif2008