如何使用 C# 創建自簽名證書？

Question

我需要使用 C# 創建一個自簽名證書（用於本地加密 - 它不用於保護通信）。

我已經看到一些使用P/Invoke和Crypt32.dll 的實現，但它們很復雜並且很難更新參數 - 如果可能的話，我也想避免 P/Invoke 。

我不需要跨平台的東西——只在 Windows 上運行對我來說已經足夠了。

理想情況下，結果將是一個 X509Certificate2 對象，我可以使用它插入到 Windows 證書存儲或導出到PFX文件。

Answer 1

從 .NET 4.7.2 開始，您可以使用System.Security.Cryptography.X509Certificates.CertificateRequest創建自簽名證書。

例如：

using System;
using System.IO;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;

public class CertificateUtil
{
    static void MakeCert()
    {
        var ecdsa = ECDsa.Create(); // generate asymmetric key pair
        var req = new CertificateRequest("cn=foobar", ecdsa, HashAlgorithmName.SHA256);
        var cert = req.CreateSelfSigned(DateTimeOffset.Now, DateTimeOffset.Now.AddYears(5));

        // Create PFX (PKCS #12) with private key
        File.WriteAllBytes("c:\\temp\\mycert.pfx", cert.Export(X509ContentType.Pfx, "P@55w0rd"));

        // Create Base 64 encoded CER (public key only)
        File.WriteAllText("c:\\temp\\mycert.cer",
            "-----BEGIN CERTIFICATE-----\r\n"
            + Convert.ToBase64String(cert.Export(X509ContentType.Cert), Base64FormattingOptions.InsertLineBreaks)
            + "\r\n-----END CERTIFICATE-----");
    }
}

Answer 2

此實現使用CX509CertificateRequestCertificate COM對象（和朋友- MSDN文檔）從certenroll.dll創建一個自簽名的證書請求和簽署。

下面的示例非常簡單（如果您忽略這里發生的 COM 內容），並且代碼中有一些部分是真正可選的（例如 EKU），它們仍然有用且易於使用適應您的使用。

public static X509Certificate2 CreateSelfSignedCertificate(string subjectName)
{
    // create DN for subject and issuer
    var dn = new CX500DistinguishedName();
    dn.Encode("CN=" + subjectName, X500NameFlags.XCN_CERT_NAME_STR_NONE);

    // create a new private key for the certificate
    CX509PrivateKey privateKey = new CX509PrivateKey();
    privateKey.ProviderName = "Microsoft Base Cryptographic Provider v1.0";
    privateKey.MachineContext = true;
    privateKey.Length = 2048;
    privateKey.KeySpec = X509KeySpec.XCN_AT_SIGNATURE; // use is not limited
    privateKey.ExportPolicy = X509PrivateKeyExportFlags.XCN_NCRYPT_ALLOW_PLAINTEXT_EXPORT_FLAG;
    privateKey.Create();

    // Use the stronger SHA512 hashing algorithm
    var hashobj = new CObjectId();
    hashobj.InitializeFromAlgorithmName(ObjectIdGroupId.XCN_CRYPT_HASH_ALG_OID_GROUP_ID,
        ObjectIdPublicKeyFlags.XCN_CRYPT_OID_INFO_PUBKEY_ANY, 
        AlgorithmFlags.AlgorithmFlagsNone, "SHA512");

    // add extended key usage if you want - look at MSDN for a list of possible OIDs
    var oid = new CObjectId();
    oid.InitializeFromValue("1.3.6.1.5.5.7.3.1"); // SSL server
    var oidlist = new CObjectIds();
    oidlist.Add(oid);
    var eku = new CX509ExtensionEnhancedKeyUsage();
    eku.InitializeEncode(oidlist); 

    // Create the self signing request
    var cert = new CX509CertificateRequestCertificate();
    cert.InitializeFromPrivateKey(X509CertificateEnrollmentContext.ContextMachine, privateKey, "");
    cert.Subject = dn;
    cert.Issuer = dn; // the issuer and the subject are the same
    cert.NotBefore = DateTime.Now;
    // this cert expires immediately. Change to whatever makes sense for you
    cert.NotAfter = DateTime.Now; 
    cert.X509Extensions.Add((CX509Extension)eku); // add the EKU
    cert.HashAlgorithm = hashobj; // Specify the hashing algorithm
    cert.Encode(); // encode the certificate

    // Do the final enrollment process
    var enroll = new CX509Enrollment();
    enroll.InitializeFromRequest(cert); // load the certificate
    enroll.CertificateFriendlyName = subjectName; // Optional: add a friendly name
    string csr = enroll.CreateRequest(); // Output the request in base64
    // and install it back as the response
    enroll.InstallResponse(InstallResponseRestrictionFlags.AllowUntrustedCertificate,
        csr, EncodingType.XCN_CRYPT_STRING_BASE64, ""); // no password
    // output a base64 encoded PKCS#12 so we can import it back to the .Net security classes
    var base64encoded = enroll.CreatePFX("", // no password, this is for internal consumption
        PFXExportOptions.PFXExportChainWithRoot);

    // instantiate the target class with the PKCS#12 data (and the empty password)
    return new System.Security.Cryptography.X509Certificates.X509Certificate2(
        System.Convert.FromBase64String(base64encoded), "", 
        // mark the private key as exportable (this is usually what you want to do)
        System.Security.Cryptography.X509Certificates.X509KeyStorageFlags.Exportable
    );
}

結果可以使用X509Store添加到證書存儲或使用X509Certificate2方法導出。

對於完全托管且不綁定到 Microsoft 的平台，並且如果您對 Mono 的許可沒有意見，那么您可以查看Mono.Security中的X509CertificateBuilder 。 Mono.Security 獨立於 Mono，因為它不需要 Mono 的其余部分來運行，並且可以在任何兼容的 .Net 環境中使用（例如 Microsoft 的實現）。

Answer 3

另一種選擇是使用 CodePlex 的CLR 安全擴展庫，它實現了一個輔助函數來生成自簽名 X.509 證書：

X509Certificate2 cert = CngKey.CreateSelfSignedCertificate(subjectName);

您還可以查看該函數的實現（在CngKeyExtensionMethods.cs ）以了解如何在托管代碼中顯式創建自簽名證書。

Answer 4

您可以使用免費的PluralSight.Crypto 庫來簡化自簽名 X.509 證書的編程創建：

    using (CryptContext ctx = new CryptContext())
    {
        ctx.Open();

        X509Certificate2 cert = ctx.CreateSelfSignedCertificate(
            new SelfSignedCertProperties
            {
                IsPrivateKeyExportable = true,
                KeyBitLength = 4096,
                Name = new X500DistinguishedName("cn=localhost"),
                ValidFrom = DateTime.Today.AddDays(-1),
                ValidTo = DateTime.Today.AddYears(1),
            });

        X509Certificate2UI.DisplayCertificate(cert);
    }

PluralSight.Crypto 需要 .NET 3.5 或更高版本。

Answer 5

如果它對其他人有幫助，我需要生成 PEM 格式的測試證書（因此需要 crt 和密鑰文件），使用Duncan Smart的答案，我生成了以下內容...

public static void MakeCert(string certFilename, string keyFilename)
{
    const string CRT_HEADER = "-----BEGIN CERTIFICATE-----\n";
    const string CRT_FOOTER = "\n-----END CERTIFICATE-----";

    const string KEY_HEADER = "-----BEGIN RSA PRIVATE KEY-----\n";
    const string KEY_FOOTER = "\n-----END RSA PRIVATE KEY-----";

    using var rsa = RSA.Create();
    var certRequest = new CertificateRequest("cn=test", rsa, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);

    // We're just going to create a temporary certificate, that won't be valid for long
    var certificate = certRequest.CreateSelfSigned(DateTimeOffset.Now, DateTimeOffset.Now.AddDays(1));

    // export the private key
    var privateKey = Convert.ToBase64String(rsa.ExportRSAPrivateKey(), Base64FormattingOptions.InsertLineBreaks);

    File.WriteAllText(keyFilename, KEY_HEADER + privateKey + KEY_FOOTER);

    // Export the certificate
    var exportData = certificate.Export(X509ContentType.Cert);

    var crt = Convert.ToBase64String(exportData, Base64FormattingOptions.InsertLineBreaks);
    File.WriteAllText(certFilename, CRT_HEADER + crt + CRT_FOOTER);
}

Answer 6

根據此處找到的代碼使用SubjectAlternativeNames擴展0909EMs 答案： 了解 c# 中的自簽名證書

        public static void MakeCert(string certFilename, string keyFilename)
        {
            const string CRT_HEADER = "-----BEGIN CERTIFICATE-----\n";
            const string CRT_FOOTER = "\n-----END CERTIFICATE-----";

            const string KEY_HEADER = "-----BEGIN RSA PRIVATE KEY-----\n";
            const string KEY_FOOTER = "\n-----END RSA PRIVATE KEY-----";

            using var rsa = RSA.Create();
            var certRequest = new CertificateRequest("cn=test", rsa, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);

            // Adding SubjectAlternativeNames (SAN)
            var subjectAlternativeNames = new SubjectAlternativeNameBuilder();
            subjectAlternativeNames .AddDnsName("test");
            certRequest.CertificateExtensions.Add(subjectAlternativeNames.Build());

            // We're just going to create a temporary certificate, that won't be valid for long
            var certificate = certRequest.CreateSelfSigned(DateTimeOffset.Now, DateTimeOffset.Now.AddDays(1));

            // export the private key
            var privateKey = Convert.ToBase64String(rsa.ExportRSAPrivateKey(), Base64FormattingOptions.InsertLineBreaks);

            File.WriteAllText(keyFilename, KEY_HEADER + privateKey + KEY_FOOTER);

            // Export the certificate
            var exportData = certificate.Export(X509ContentType.Cert);

            var crt = Convert.ToBase64String(exportData, Base64FormattingOptions.InsertLineBreaks);
            File.WriteAllText(certFilename, CRT_HEADER + crt + CRT_FOOTER);
        }

對於使用X509KeyUsageExtension的密鑰用法的定義，請看這里https://stackoverflow.com/a/48210587/226278

Answer 7

這是關於如何創建證書的 Powershell 版本。 您可以通過執行命令來使用它。 檢查https://technet.microsoft.com/itpro/powershell/windows/pkiclient/new-selfsignedcertificate

編輯：忘了說，創建證書后，您可以使用Windows“管理計算機證書”程序，將證書導出為.CER或其他類型。