using System;

using System.IO;

using System.Text;

using Org.BouncyCastle.Crypto;

using Org.BouncyCastle.OpenSsl;

using Org.BouncyCastle.Security;

using Org.BouncyCastle.X509;

namespace security_sandbox

{

    class Program

    {

        static void Main(string[] args)

        {

            var certificateString =  @"-----BEGIN CERTIFICATE-----

MIIB4TCCAYegAwIBAgIUKt0WdaKI2eRXBO2nVk+OF6AZqHMwCgYIKoZIzj0EAwIw

RTELMAkGA1UEBhMCQVUxEzARBgNVBAgMClNvbWUtU3RhdGUxITAfBgNVBAoMGElu

dGVybmV0IFdpZGdpdHMgUHR5IEx0ZDAgFw0yMDA1MDcxMzM2MTNaGA8yMTIwMDQx

MzEzMzYxM1owRTELMAkGA1UEBhMCQVUxEzARBgNVBAgMClNvbWUtU3RhdGUxITAf

BgNVBAoMGEludGVybmV0IFdpZGdpdHMgUHR5IEx0ZDBZMBMGByqGSM49AgEGCCqG

SM49AwEHA0IABO39ccEC+Zv1HDeMy/s7JculdYN/8DXC+U3Qn1rdF351H4NMfkbC

H9bnqwZ4a5oR9HDfaNMX14OQd4VERZV1bhGjUzBRMB0GA1UdDgQWBBRGuUmsyB2h

JCXMRTVMRTcdoWZQaDAfBgNVHSMEGDAWgBRGuUmsyB2hJCXMRTVMRTcdoWZQaDAP

BgNVHRMBAf8EBTADAQH/MAoGCCqGSM49BAMCA0gAMEUCIGG8tQZlh7aJaI34Y7jq

44SmSc/ule9MgjIX+Gg+i5vwAiEA9Jb/304KO4t9OMqFMQeWZXIHdzhDFBwx7FWz

78+UsnY=

-----END CERTIFICATE-----";

            var pemreader = new PemReader(new StringReader(certificateString));

            var cert = (X509Certificate)pemreader.ReadObject();

            // Alternatively, load the public key directly

            var pubkeyString =

@"-----BEGIN PUBLIC KEY-----

MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE7f1xwQL5m/UcN4zL+zsly6V1g3/w

NcL5TdCfWt0XfnUfg0x+RsIf1uerBnhrmhH0cN9o0xfXg5B3hURFlXVuEQ==

-----END PUBLIC KEY-----";

            pemreader = new PemReader(new StringReader(pubkeyString));

            var pubkey = (AsymmetricKeyParameter)pemreader.ReadObject();

            var data = "Hello";

            var signature = Convert.FromBase64String("MEUCIQD5593C/NBhHA1DILT72gjhGj/lKjom9vYP+JbuypBrxQIgNAjYT1LihEpPbUhe1n9ccUHQvw676bGqOTEU/25qcRQ=");

            // Verify using the public key

            var signer = SignerUtilities.GetSigner("SHA-256withECDSA");

            signer.Init(false, pubkey);

            signer.BlockUpdate(Encoding.ASCII.GetBytes(data), 0, data.Length);

            var success = signer.VerifySignature(signature);

            if (success) {

                Console.WriteLine("Signature verified successfully using public key");

            } else {

                Console.WriteLine("Failed to verify signature using public key");

            }

            // Verify using the certificate - the certificate's public key is extracted using the GetPublicKey method.

            signer.Init(false, cert.GetPublicKey());

            signer.BlockUpdate(Encoding.ASCII.GetBytes(data), 0, data.Length);

            success = signer.VerifySignature(signature);

            if (success) {

                Console.WriteLine("Signature verified successfully using certificate");

            } else {

                Console.WriteLine("Failed to verify signature using certificate");

            }

        }

    }

}