private void NegotiateKey(ConnectedClient selectedClient)
{
var synMessage = new EncMessage()
{
Sender = new ConnectedClient()
{
Id = _userId,
Username = _username
},
Recipient = selectedClient,
UsedForDHExchange = true,
Payload = new byte[1] {
0x34
}
};
_serverChannel.SendMessage(synMessage);
byte[] rndBytes = new byte[32];
RNGCryptoServiceProvider.Create().GetBytes(rndBytes);
privateKey = Curve25519.ClampPrivateKey(rndBytes);
byte[] publicKey = Curve25519.GetPublicKey(privateKey);
synMessage.Payload = publicKey;
_serverChannel.SendMessage(synMessage);
}
private void DisplayNewMessage(EncMessage message)
{
if (!message.UsedForDHExchange)
{
// TODO: Here we will decrypt the message and show it
using (Aes aes = Aes.Create())
{
this.messagesListBox.Items.Add($"{message.Sender.Username}> " +
$"{AesEncryption.DecryptStringFromBytes(message.Payload, _clientsPrivateKeys[message.Sender.Username], new byte[16])}");
}
}
else
{
if (message.Payload[0] == 0x34 && message.Payload.Length == 1)
{
byte[] rndBytes = new byte[32];
RNGCryptoServiceProvider.Create().GetBytes(rndBytes);
privateKey = Curve25519.ClampPrivateKey(rndBytes);
byte[] publicKey = Curve25519.GetPublicKey(privateKey);
var pubKeyMessage = new EncMessage()
{
Recipient = message.Sender,
Sender = message.Recipient,
UsedForDHExchange = true,
Payload = publicKey
};
_serverChannel.SendMessage(pubKeyMessage);
}
else
{
if (!_clientsPrivateKeys.ContainsKey(message.Sender.Username))
{
_clientsPrivateKeys[message.Sender.Username] = Curve25519.GetSharedSecret(privateKey, message.Payload);
}
}
}
}
private void sendButton_Click(object sender, EventArgs e)
{
if (string.IsNullOrWhiteSpace(messageTextBox.Text) || (messageTextBox.Text == "Write a message"))
{
MessageBox.Show("Please enter a message first.", "Warning", MessageBoxButton.OK, MessageBoxImage.Exclamation);
return;
}
var selectedClientRecipient = clientsListBox.SelectedItem as ConnectedClient;
if (selectedClientRecipient == null)
{
MessageBox.Show("Please select a recipient first.", "Warning", MessageBoxButton.OK, MessageBoxImage.Exclamation);
return;
}
// TODO: Here we will encrypt the message
using (Aes aes = Aes.Create())
{
var encryptedMessage = new EncMessage()
{
UsedForDHExchange = false,
Payload = AesEncryption.EncryptStringToBytes(messageTextBox.Text, _clientsPrivateKeys[selectedClientRecipient.Username], new byte[16]),
Recipient = selectedClientRecipient,
Sender = new ConnectedClient()
{
Id = _userId,
Username = _username
}
};
_serverChannel.SendMessage(encryptedMessage);
}
messagesListBox.Items.Add($"Me> {messageTextBox.Text}");
messageTextBox.Clear();
}
