using Org.BouncyCastle.Crypto;

using Org.BouncyCastle.Security;

using System;

public class Program

{

    public static void Main()

    {

        // Import key (as X.509)

        string pubBody = "MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEOcPddBMXKURtwbPaZ9SfwEb8vwcvzFufpRwFuXQwf5acQDsWNfBEnwK9QidR4zEhpENPFS8rKyo/Z1IZxdkl9g=="; // corresponds to 0439c3dd74131729446dc1b3da67d49fc046fcbf072fcc5b9fa51c05b974307f969c403b1635f0449f02bd422751e33121a4434f152f2b2b2a3f675219c5d925f6, s. e.g. https://lapo.it/asn1js

        byte[] pubDer = Convert.FromBase64String(pubBody);

        AsymmetricKeyParameter publicKey = PublicKeyFactory.CreateKey(pubDer);

        // Import message and signature

        byte[] messageBytes = new byte[]{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F};

        byte[] signature = new byte[]{0xD6,0x82,0x25,0xCC,0x68,0x6F,0x4F,0x84,0x91,0x48,0x63,0x6E,0x67,0x3C,0xD4,0xC0,0xF8,0xE5,0x9D,0x7B,0xAD,0x6B,0xB3,0xF1,0x1C,0xDB,0x90,0xB7,0x1A,0x5E,0x43,0xCF,0xD8,0xC3,0x8C,0x77,0x74,0xE2,0xA0,0x29,0xFF,0x43,0x22,0x7D,0xF9,0x41,0x56,0x12,0x8A,0x1B,0xEA,0x4D,0x57,0x8A,0x37,0x9C,0x6A,0x85,0x0A,0x56,0xBE,0xEC,0x1A,0x69};

​

        // Verify unhshed data with (r,s)-signature (NoneWithPLAIN-ECDSA)

        ISigner signer = SignerUtilities.GetSigner("NoneWithPLAIN-ECDSA");

        signer.Init(false, publicKey);

        signer.BlockUpdate(messageBytes, 0, messageBytes.Length);

        bool verified = signer.VerifySignature(signature);                

        Console.WriteLine(verified);

    }

}