using System;

using System.Security.Cryptography;

using System.Security.Cryptography.X509Certificates;

​

class Program

{

    static void Main()

    {

        // Replace the following variables with your actual input values

        string privateKeyPEM = @"

            -----BEGIN EC PRIVATE KEY-----

MHcCAQEEIDfkJ9UjKHSzEbw0smXwGlyOwsw/NT+y/0Ke7h+AseLkoAoGCCqGSM49

AwEHoUQDQgAER0V+sLtPEIU1hSkHszfbvwxnq7JYL4JQQOIe1yJXBly5ONzaD0aE

0OzoutaLXgfKi/WFoINS9REPVA2AtjW5bA==

            -----END EC PRIVATE KEY-----

        ";

​

        string subjectDN = "CN=test, C=Japan";

        DateTime startDate = DateTime.Now;

        DateTime endDate = startDate.AddDays(365); // Certificate valid for 1 year

​

        // Convert PEM private key to ECDsa object

        ECDsa privateKey = CryptoHelper.GetECDsaFromPEM(privateKeyPEM);

​

        // Generate self-signed certificate

        X509Certificate2 certificate = CryptoHelper.GenerateSelfSignedCertificate(privateKey, subjectDN, startDate, endDate);

​

        // Convert certificate to base64 string

        string base64Certificate = Convert.ToBase64String(certificate.Export(X509ContentType.Cert));

​

        Console.WriteLine(base64Certificate + "\nFinished");

    }

}

​

public static class CryptoHelper

{

    public static ECDsa GetECDsaFromPEM(string privateKeyPEM)

    {

        ECDsa ecdsaPrivateKey = ECDsa.Create();

        ecdsaPrivateKey.ImportFromPem(privateKeyPEM);

        return ecdsaPrivateKey;

    }

​

    public static X509Certificate2 GenerateSelfSignedCertificate(ECDsa privateKey, string subjectDN, DateTime startDate, DateTime endDate)

    {

        var request = new CertificateRequest(subjectDN, privateKey, HashAlgorithmName.SHA256);

​

        request.CertificateExtensions.Add(

            new X509BasicConstraintsExtension(false, false, 0, false));

​

        var certificate = request.CreateSelfSigned(startDate, endDate);

​

        return new X509Certificate2(certificate.Export(X509ContentType.Pfx), "", X509KeyStorageFlags.Exportable);

    }

}

​