Demonstrates how to use BouncyCastle with brainpoolp256r1 curve

brainpoolp256r1.cs

namespace microsoft.chgeuer.crypto
{
    
    // compile this baby against https://github.com/bcgit/bc-csharp
    // or against NuGet <package id="BouncyCastle" version="1.7.0" targetFramework="net45" />
    
    using Org.BouncyCastle.Asn1.X9;
    using Org.BouncyCastle.Crypto.Generators;
    using Org.BouncyCastle.Crypto.Parameters;
    using Org.BouncyCastle.Security;
    using System;
    using System.Collections.Generic;
    using System.Text;

    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                var algorithm = "brainpoolp256r1";
                X9ECParameters brainpoolp256r1Params = ECNamedCurveTable.GetByName(algorithm);

                var keyParams = new ECKeyGenerationParameters(
                    domainParameters: new ECDomainParameters(
                        curve: brainpoolp256r1Params.Curve,
                        g: brainpoolp256r1Params.G,
                        n: brainpoolp256r1Params.N,
                        h: brainpoolp256r1Params.H),
                    random: new SecureRandom());

                var gen = new ECKeyPairGenerator();
                gen.Init(keyParams);
                var key = gen.GenerateKeyPair();


                string plainText = "Hello World öäü";
                var inputData = Encoding.UTF8.GetBytes(plainText);

                var privateKey = (ECPrivateKeyParameters)(key.Private);
                var signature = GetSignature(inputData, privateKey);


                var publicKey = (ECPublicKeyParameters)(key.Public);
                var signatureOK = VerifySignature(inputData, publicKey, signature);

                Console.WriteLine(string.Format("======= Key Size: {0} =======", keyParams.Strength));
                Console.WriteLine("Input Text: " + plainText);
                Console.WriteLine("Key ({0} bytes): {1}", privateKey.D.BitLength, privateKey.D);
                Console.WriteLine("Signature ({0} bytes): {1}", signature.Length, ToHexString(signature));
                Console.WriteLine("Signature verified: {0}", signatureOK);
                Console.WriteLine();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            Console.ReadLine();
        }

        private static byte[] GetSignature(byte[] inputData, ECPrivateKeyParameters privateKey)
        {
            var signer = SignerUtilities.GetSigner("ECDSA");
            signer.Init(true, privateKey);
            signer.BlockUpdate(inputData, 0, inputData.Length);

            return signer.GenerateSignature();
        }

        private static bool VerifySignature(byte[] inputData, ECPublicKeyParameters publicKey, byte[] signature)
        {
            var signer = SignerUtilities.GetSigner("ECDSA");
            signer.Init(false, publicKey);
            signer.BlockUpdate(inputData, 0, inputData.Length);

            return signer.VerifySignature(signature);
        }

        private static string ToHexString(IEnumerable<byte> b)
        {
            var sb = new StringBuilder();
            foreach (byte b1 in b)
            {
                sb.Append(b1.ToString("X2"));
            }
            return sb.ToString();
        }
    }
}