如何在 .NET Core 中生成对 CSR 的响应（即编写 CSR 签名服务器）？

Question

我正在通过 Nuget 包学习证书签名请求和签名服务器 System.Security.Cryptography.Cng。还有什么比尝试重新创建一个更好的方法。目前似乎有一个我没有解决的问题，那就是服务器签名方，即在下面的代码中，我在 using 子句中的 request.Create( 处得到 System.InvalidOperationException: 'An X509Extension with OID '2.5.29.37' has already been specified.' 。我在 http://oid-info.com/get/2.5.29.37 看到它是关于扩展密钥使用的。

问题：

1. MakeLocalhostCert 可能是错误的，应该如何更改才能使其成为签署 CSR 的证书？
2. 是否可以add/remove extensions/OIDs返回CSR？我相信是的，但不知何故这部分目前让我望而却步。

我使用了 https://whosebug.com/users/6535399/bartonjs at and at 的出色答案才走到这一步。 :)

    private static void CsrSigningTest()
    {
        //Both ECDSA and RSA included here, though ECDSA is probably better.
        using(ECDsa privateClientEcdsaKey = ECDsa.Create(ECCurve.NamedCurves.nistP256))
        //using(RSA privateClientRsaKey = RSA.Create(2048))
        {
            //A client creates a certificate signing request.
            CertificateRequest request = new CertificateRequest(
                new X500DistinguishedName("CN=example.com, O=Example Ltd, OU=AllOver, L=Sacremento, ST=\"California\", C=US, E=some@example.com"),
                privateClientEcdsaKey,
                HashAlgorithmName.SHA256);
            /*CertificateRequest request = new CertificateRequest(
                new X500DistinguishedName("CN=example.com, O=Example Ltd, OU=AllOver, L=Sacremento, ST=\"California\", C=US, E=some@example.com"),
                privateClientRsaKey,
                HashAlgorithmName.SHA256,
                RSASignaturePadding.Pkcs1);*/

            var sanBuilder = new SubjectAlternativeNameBuilder();
            sanBuilder.AddDnsName("example.com");
            request.CertificateExtensions.Add(sanBuilder.Build());

            //Not a CA, a server certificate.
            request.CertificateExtensions.Add(new X509BasicConstraintsExtension(false, false, 0, false));
            request.CertificateExtensions.Add(new X509EnhancedKeyUsageExtension(new OidCollection { new Oid("1.3.6.1.5.5.7.3.1") }, false));
            request.CertificateExtensions.Add(new X509EnhancedKeyUsageExtension(new OidCollection { new Oid("1.3.6.1.5.5.7.3.8") }, false));

            byte[] derEncodedCsr = request.CreateSigningRequest();
            var csrSb = new StringBuilder();
            csrSb.AppendLine("-----BEGIN CERTIFICATE REQUEST-----");
            csrSb.AppendLine(Convert.ToBase64String(derEncodedCsr));
            csrSb.AppendLine("-----END CERTIFICATE REQUEST-----");

            //Thus far OK, this csr seems to be working when using an online checker.
            var csr = csrSb.ToString();

            //Now, sending this to a server... How does the server function:
            //1) Read the CSR to be processed?
            //2) How does this CSR get signed?
            //In the following, can the signing cert be self-signed could be had from
            //

            byte[] serial = new byte[16];
            using(var rng = RandomNumberGenerator.Create())
            {
                rng.GetBytes(serial);
            }

            DateTimeOffset notBefore = DateTimeOffset.UtcNow;
            DateTimeOffset notAfter = notBefore.AddYears(1);
            var issuerCertificate = MakeLocalhostCert();
            //For the part 1) there, this doesn't seem to work, likely since CSR isn't a X509 certificate.
            //But then again, there doesn't seem to be anything in CertificateRequest to read this.
            //In reality in the server the prologue and epilogue strings should be removed and the string read.
            //var testRequest = new X509Certificate2(derEncodedCsr);
            using(X509Certificate2 responseToCsr = request.Create(issuerCertificate, notBefore, notAfter, serial))
            {
                //How to add extensions here?
                var csrResSb = new StringBuilder();
                csrResSb.AppendLine("-----BEGIN CERTIFICATE-----");
                csrResSb.AppendLine(Convert.ToBase64String(responseToCsr.GetRawCertData()));
                csrResSb.AppendLine("-----END CERTIFICATE-----");

                var signedCert = csrResSb.ToString();
            }
        }
    }

    private static X509Certificate2 MakeLocalhostCert()
    {
        using(ECDsa key = ECDsa.Create(ECCurve.NamedCurves.nistP384))
        {
            var request = new CertificateRequest(
                "CN=localhost",
                key,
                HashAlgorithmName.SHA384);

            request.CertificateExtensions.Add(
                new X509BasicConstraintsExtension(true, false, 0, true));

            const X509KeyUsageFlags endEntityTypicalUsages =
                X509KeyUsageFlags.DataEncipherment |
                X509KeyUsageFlags.KeyEncipherment |
                X509KeyUsageFlags.DigitalSignature |
                X509KeyUsageFlags.NonRepudiation |
                X509KeyUsageFlags.KeyCertSign;

            request.CertificateExtensions.Add(
                new X509KeyUsageExtension(endEntityTypicalUsages, true));

            var sanBuilder = new SubjectAlternativeNameBuilder();
            sanBuilder.AddDnsName("localhost");
            sanBuilder.AddIpAddress(IPAddress.Loopback);
            sanBuilder.AddIpAddress(IPAddress.IPv6Loopback);

            request.CertificateExtensions.Add(sanBuilder.Build());

            /*request.CertificateExtensions.Add(
                new X509EnhancedKeyUsageExtension(
                    new OidCollection
                    {
                // server and client authentication
                new Oid("1.3.6.1.5.5.7.3.1"),
                new Oid("1.3.6.1.5.5.7.3.2")
                    },
                    false));*/

            DateTimeOffset now = DateTimeOffset.UtcNow.AddMinutes(-1);

            return request.CreateSelfSigned(now, now.AddYears(2));
        }
    }

一旦我应用了关于 OID 的修复并将最后一位更改为

using(X509Certificate2 responseToCsr = request.Create(issuerCertificate, notBefore, notAfter, serial))
            {
                request.CertificateExtensions.Add(new X509SubjectKeyIdentifierExtension(issuerCertificate.PublicKey, false));
                var csrResSb = new StringBuilder();
                csrResSb.AppendLine("-----BEGIN CERTIFICATE-----");
                csrResSb.AppendLine(Convert.ToBase64String(responseToCsr.Export(X509ContentType.Cert), Base64FormattingOptions.InsertLineBreaks));
                csrResSb.AppendLine("-----END CERTIFICATE-----");

                var signedCert = csrResSb.ToString();
            }

我在 signedCert 中取回了一份证书，看起来像已签署的 CSR。如果从实际的 CSR 文件中读取，则缺少的部分是构建 CSR。

CoreFx GH 中存在一个问题，跟踪此处涉及的一些问题：Security crypto - Roadmap。

很高兴知道：, How to convert a CSR text file into .NET Core/ Standard CertificateRequest for Signing?, How to convert a CSR text file into .NET Core/ Standard CertificateRequest for Signing? 有关更多信息，请参见 .NET5/6.

Answer 1

要修复您的异常，您希望您的代码设置一个具有两个目的 OID 的 EKU 扩展，而不是两个各有一个的扩展。

// Defined two EKU extensions
request.CertificateExtensions.Add(new X509EnhancedKeyUsageExtension(new OidCollection { new Oid("1.3.6.1.5.5.7.3.1") }, false));
request.CertificateExtensions.Add(new X509EnhancedKeyUsageExtension(new OidCollection { new Oid("1.3.6.1.5.5.7.3.8") }, false));

至

// One extension carrying multiple purpose OIDs
request.CertificateExtensions.Add(
    new X509EnhancedKeyUsageExtension(
        new OidCollection
        {
            new Oid("1.3.6.1.5.5.7.3.1"),
            new Oid("1.3.6.1.5.5.7.3.8"),
        },
        false));

那么你的 title/question 中还有一些其他问题：

• "How to generate a response to a CSR in .NET Core (i.e. to write a CSR signing server)?"
  • 此代码未读取 CSR，因此未对 CSR 做出响应。
    • class 的目的是满足单元测试和其他开发环境需求，并能够生成 CSR 以发送到真正的 CA 产品。
    • .NET Core 甚至无法读取 CSR，只能编写它们。
• "I'm learning about certificate signing requests and signing servers via Nuget package System.Security.Cryptography.Cng"
  • None 你的代码似乎使用了 Cng 类型（这很好，你应该很少关心）。 CertificateRequest 是 System.Security.Cryptography.X509Certificates.dll 的一部分，通过 Microsoft.NETCore.App
  公开
• "Is it possible to add/remove extensions/OIDs to the CSR being returned?"
  • 是的，您在调用 CreateSigningRequest 之前将它们添加到 CertificateExtensions 属性。
• （隐含）"Is it possible to add/remove extensions/OIDs to the certificate being returned?"
  • 是的，您在调用 Create 或 CreateSelfSigned 之前将它们添加到 CertificateExtensions 属性。