.NET implementation (libraries) of elliptic curve cryptography

Question

Please can you suggest any implementation of elliptical curve cryptography to be used on .NET platform?

Also if you have used them, can you tell me the recommended curve

Answer 1

Great! I tried it but cant find how to use it to encrypt a message. Doesn't seem to have any "Encrypt" function

This the MSDN sample for System.Security.Cryptography.ECDiffieHellmanCng.

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;


class Alice
{
    public static byte[] alicePublicKey;

    public static void Main(string[] args)
    {
        using (ECDiffieHellmanCng alice = new ECDiffieHellmanCng())
        {

            alice.KeyDerivationFunction = ECDiffieHellmanKeyDerivationFunction.Hash;
            alice.HashAlgorithm = CngAlgorithm.Sha256;
            alicePublicKey = alice.PublicKey.ToByteArray();
            Bob bob = new Bob();
            CngKey k = CngKey.Import(bob.bobPublicKey, CngKeyBlobFormat.EccPublicBlob);
            byte[] aliceKey = alice.DeriveKeyMaterial(CngKey.Import(bob.bobPublicKey, CngKeyBlobFormat.EccPublicBlob));
            byte[] encryptedMessage = null;
            byte[] iv = null;
            Send(aliceKey, "Secret message", out encryptedMessage, out iv);
            bob.Receive(encryptedMessage, iv);
        }

    }

    private static void Send(byte[] key, string secretMessage, out byte[] encryptedMessage, out byte[] iv)
    {
        using (Aes aes = new AesCryptoServiceProvider())
        {
            aes.Key = key;
            iv = aes.IV;

            // Encrypt the message 
            using (MemoryStream ciphertext = new MemoryStream())
            using (CryptoStream cs = new CryptoStream(ciphertext, aes.CreateEncryptor(), CryptoStreamMode.Write))
            {
                byte[] plaintextMessage = Encoding.UTF8.GetBytes(secretMessage);
                cs.Write(plaintextMessage, 0, plaintextMessage.Length);
                cs.Close();
                encryptedMessage = ciphertext.ToArray();
            }
        }
    }

}
public class Bob 
{
    public byte[] bobPublicKey;
    private byte[] bobKey;
    public Bob()
    {
        using (ECDiffieHellmanCng bob = new ECDiffieHellmanCng())
        {

            bob.KeyDerivationFunction = ECDiffieHellmanKeyDerivationFunction.Hash;
            bob.HashAlgorithm = CngAlgorithm.Sha256;
            bobPublicKey = bob.PublicKey.ToByteArray();
            bobKey = bob.DeriveKeyMaterial(CngKey.Import(Alice.alicePublicKey, CngKeyBlobFormat.EccPublicBlob));

        }
    }

    public void Receive(byte[] encryptedMessage, byte[] iv)
    {

        using (Aes aes = new AesCryptoServiceProvider())
        {
            aes.Key = bobKey;
            aes.IV = iv;
            // Decrypt the message 
            using (MemoryStream plaintext = new MemoryStream())
            {
                using (CryptoStream cs = new CryptoStream(plaintext, aes.CreateDecryptor(), CryptoStreamMode.Write))
                {
                    cs.Write(encryptedMessage, 0, encryptedMessage.Length);
                    cs.Close();
                    string message = Encoding.UTF8.GetString(plaintext.ToArray());
                    Console.WriteLine(message);
                }
            }
        }
    }

}