生成DKIM的公钥和私钥

生成一个公钥和私钥

可以使用下述网站生成公钥和私钥（当然，使用外部网站来生成公钥和私钥是不安全的，建议仅作为测试时使用）
https://easydmarc.com/tools/dkim-record-generator

通过证书生成一个公钥和私钥

          使用OpenSSL创建证书

                    1.安装 OpenSSL：首先，在计算机上安装 OpenSSL。可以从 OpenSSL 官方网站（https://www.openssl.org/）下载适用于操作系统的适当版本。
                    2. openssl genpkey -algorithm RSA -out private.key 这将生成一个名为 private.key 的私钥文件。
                    3. 生成证书签名请求（CSR）：使用私钥生成证书签名请求（CSR），该请求包含有关您的证书的信息。使用以下命令生成 CSR 文件：
                    openssl req -new -key private.key -out csr.csr
                    4.在生成 CSR 过程中，您将需要提供一些证书的相关信息，例如组织名称、常用名称 (CN) 等。
                    自签名证书：如果您只是需要自签名证书，您可以使用以下命令生成自签名证书：
                    openssl x509 -req -days 365 -in csr.csr -signkey private.key -out certificate.crt
                    这将生成一个名为 certificate.crt 的自签名证书文件。
                    ※以上方法来自于Chatgpt,未经验证，不保证是否正确

          使用C# code创建证书

                    .Net创建证书存在限制，出于防止私钥被意外泄露的安全考虑，证书的私钥正常是无法导出的（RSACng 类的 AllowPlaintextExport 属性不再可用）
                    当然，我们也可以通过其他方式绕过这种限制，具体可以参考下面的code

                 创建证书

 1         /// <summary>
 2         /// Use this method to create a certificate
 3         /// </summary>
 4         /// <returns></returns>
 5         public static X509Certificate2 CreateCertificateWithPrivateKey()
 6         {
 7             // 创建 RSA 密钥对
 8             RSA rsa = RSA.Create();
 9 
10             // 创建证书请求
11             CertificateRequest request = new CertificateRequest("CN=My Certificate", rsa, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
12 
13             // 添加扩展名，可选
14             request.CertificateExtensions.Add(new X509BasicConstraintsExtension(false, false, 0, false));
15             request.CertificateExtensions.Add(new X509KeyUsageExtension(System.Security.Cryptography.X509Certificates.X509KeyUsageFlags.DigitalSignature, false));
16 
17             // 创建自签名证书
18             X509Certificate2 certificate = request.CreateSelfSigned(DateTimeOffset.Now.AddDays(-1), DateTimeOffset.Now.AddYears(1));
19 
20             //var content = certificate.Export(X509ContentType.Pfx, password);
21             //File.WriteAllBytes(exportPath, content);
22             return certificate;
23         }

               导出证书的私钥

/// <summary>
        /// Use this method to export private key
        /// certificate not support export private key if created by C# code
        /// use this method to support export private key
        /// refer path:https://stackoverflow.com/questions/65242917/unable-to-export-rsa-private-parameters-when-running-as-administrator
        /// for now, not find a method to support .Net Framwork to export private key.
        /// </summary>
        /// <param name="cert"></param>
        /// <returns></returns>
        public static RSA GetExportableRSAPrivateKey(X509Certificate2 cert)
        {
            const CngExportPolicies exportability = CngExportPolicies.AllowExport | CngExportPolicies.AllowPlaintextExport;

            var rsa = cert.GetRSAPrivateKey();

            // Thankfully we don't have to deal with all this shit on Linux
            if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
                return rsa;

            // We always expect an RSACng on Windows these days, but that could change
            if (!(rsa is RSACng rsaCng))
                return rsa;

            // Is the AllowPlaintextExport policy flag already set?
            if ((rsaCng.Key.ExportPolicy & exportability) != CngExportPolicies.AllowExport)
                return rsa;

            try
            {
                // Export the original RSA private key to an encrypted blob - note you will get "The requested operation
                // is not supported" if trying to export without encryption, so we export with encryption!
                var exported = rsa.ExportEncryptedPkcs8PrivateKey(nameof(GetExportableRSAPrivateKey),
                    new PbeParameters(PbeEncryptionAlgorithm.Aes256Cbc, HashAlgorithmName.SHA256, 2048));

                // Load the exported blob into a fresh RSA object, which will have the AllowPlaintextExport policy without
                // having to do anything else
                RSA copy = RSA.Create();
                copy.ImportEncryptedPkcs8PrivateKey(nameof(GetExportableRSAPrivateKey), exported, out _);

                return copy;
            }
            finally
            {
                rsa.Dispose();
            }
        }