Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;

namespace DigitalSigning
{
    class Program
    {
        static X509Certificate2 certificate = null;

        static void Main(string[] args)
        {
            try
            {
                string data = "Test data";
                
                // SIGN
                byte[] signature = Sign(data, "CN=client1");

                string digitalSignatureStr = System.Convert.ToBase64String(signature);
                Console.WriteLine("Digital sig: " + digitalSignatureStr);

                //VERIFY
                bool validSig = Verify(data, digitalSignatureStr, "");
                
                Console.WriteLine(validSig ? "Signature verified" : "Signature unverified!");
            }
            catch (Exception ex)
            {
                Console.WriteLine("EXCEPTION: " + ex.Message);
            }
            Console.ReadKey();
        }

        static byte[] Sign(string text, string certSubject)
        {
            X509Store my = new X509Store(StoreName.My, StoreLocation.CurrentUser);
            my.Open(OpenFlags.ReadOnly);

            // Find certificate
            RSACryptoServiceProvider csp = null;
            foreach (X509Certificate2 cert in my.Certificates)
            {
                if (cert.Subject.Contains(certSubject))
                {
                    certificate = cert;
                    csp = (RSACryptoServiceProvider)cert.PrivateKey;
                }
            }

            if (csp == null)
                throw new Exception("No valid cert was found");
            
            // SIGN
            RSACryptoServiceProvider rsaClear = new RSACryptoServiceProvider();
            rsaClear.ImportParameters(csp.ExportParameters(true));
            
            byte[] signature = rsaClear.SignData(Encoding.UTF8.GetBytes(text), 
                                                  CryptoConfig.CreateFromName("SHA256"));

            return signature;
        }

        static bool Verify(string text, string signature, string certPath)
        {
            RSACryptoServiceProvider csp = (RSACryptoServiceProvider)certificate.PublicKey.Key;

            return csp.VerifyData(Encoding.UTF8.GetBytes(text), 
                                    CryptoConfig.MapNameToOID("SHA256"), 
                                    System.Convert.FromBase64String(signature));

        }

    }
}

SignatureVerifier.java

	/**
	 * Tests digital signature verification
	 * 
	 */
	public void testVerifySignature_MohnishSelfCert() throws Exception {
		
		kynectServlet.setKynectSignatureAlias("");

		String data = "Test data";
		String signature = "AUyy1R9d4doirllFuzA6VFKBBNWC8/bYu9WeDvmycZB8bswRdoZvTcVAcw4/YO9XfzpVqJBLylLQHJLfNZP1vLYhGFJ9c7DRpMHsJ/LwX+PWZshb+51GciT6Acwa3VMeo2/OyxUOTSFCS8SqaQgmkIu8SogIPjRzzWKJAW0KA+A=";
		
		boolean result = false;
		
		try{
			Certificate cert = keyStore.getCertificate("mcselfcert");
			
			Signature sig = Signature.getInstance("SHA256withRSA");
			sig.initVerify(cert);
			
			byte[] dataBytes = data.getBytes("UTF-8");
			sig.update(dataBytes);
			
			byte[] sigBytes = Base64.decodeBase64(signature.getBytes("UTF-8"));
			result = sig.verify(sigBytes);

		}catch(Exception e) {
			e.printStackTrace();
		}
		
		assertTrue("Signatures don't match!", result);
		
	}