// format: 27 char: hash, 6 char: ID, 12 char: count, rest for message;
public static string FormMessage(ulong messageNumber, string text, bool isServer)
{
var toHash = (isServer ? SERVER_ID : CLIENT_ID)
+ Convert.ToBase64String(BitConverter.GetBytes(messageNumber))
+ text;
return(HashedMessage.FormMessage(toHash));
}
/// <summary>
/// Client:
/// 1) send: "client"||R1
/// 2) recieve R2 || HE("server" || R1, K_pass)
/// 2.1 check R1
/// 2.2 check ID_server for "server" and size
/// 3) send HE("client" || R2 || RSA_public, k_pass)
/// 4) recieve HE("server" || E(Key_session || IV_session, RSA_public), k_pass)
///
/// HE(x||y, k) --> E(H(x||y)||x||y, k)
///
/// </summary>
/// <returns>true if key exchange is succssesful</returns>
public bool exchangeKeys()
{
sessionId_ = isServer ? SERVER : CLIENT;
if (isServer)
{
string messageRecieved = streamReader.ReadLine(); //1
var others_sessionID = messageRecieved.Substring(0, SESSION_ID_LENGTH);
string random1 = messageRecieved.Substring(SESSION_ID_LENGTH);
if (random1.Length != RANDOM_SIZE_BASE64)
{
return(false);
}
if (others_sessionID != CLIENT)
{
return(false);
}
string random2 = generateRandomString(RANDOM_SIZE_BYTES);
string messageEncrypted = passAES.Encrypt(HashedMessage.FormMessage(sessionId_ + random1));
streamWriter.WriteLine(random2 + messageEncrypted); //2
streamWriter.Flush();
var hashedMessage = new HashedMessage(passAES.Decrypt(streamReader.ReadLine())); //3
messageRecieved = hashedMessage.Message;
if (!hashedMessage.hashMatched)
{
return(false);
}
if (messageRecieved.Substring(0, SESSION_ID_LENGTH) != others_sessionID)
{
return(false);
}
string receivedRandom2 = messageRecieved.Substring(SESSION_ID_LENGTH, RANDOM_SIZE_BASE64);
if (random2 != receivedRandom2)
{
return(false);
}
string rsaPublic = messageRecieved.Substring(SESSION_ID_LENGTH + RANDOM_SIZE_BASE64);
RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
rsa.FromXmlString(rsaPublic);
if (verbose)
{
Console.WriteLine("RSA Public Key: " + rsaPublic + "\n");
}
sessionAES = new SimpleAES(aesKeySize);
sessionAES.verbose = verbose;
string encryptedPart = Convert.ToBase64String(rsa.Encrypt(sessionAES.key, true));
streamWriter.WriteLine(passAES.Encrypt(HashedMessage.FormMessage(sessionId_ + encryptedPart))); //4
streamWriter.Flush();
if (verbose)
{
Console.WriteLine("SessionKey: " + Convert.ToBase64String(sessionAES.key));
}
}
else ///client
{
string random1 = generateRandomString(RANDOM_SIZE_BYTES);
streamWriter.WriteLine(sessionId_ + random1); // 1
streamWriter.Flush();
string messageRecieved = streamReader.ReadLine(); //2
string random2 = messageRecieved.Substring(0, RANDOM_SIZE_BASE64);
string messageEncrypted = messageRecieved.Substring(RANDOM_SIZE_BASE64);
messageRecieved = passAES.Decrypt(messageEncrypted); // ID_server || R1
var hashedMessage = new HashedMessage(messageRecieved);
messageRecieved = hashedMessage.Message;
if (!hashedMessage.hashMatched)
{
return(false);
}
var others_sessionID = messageRecieved.Substring(0, SESSION_ID_LENGTH);
if (others_sessionID != SERVER) //2.2
{
return(false);
}
string recievedRandom1 = messageRecieved.Substring(SESSION_ID_LENGTH);
if (recievedRandom1 != random1) // 2.1
{
return(false);
}
RSACryptoServiceProvider rsa = new RSACryptoServiceProvider(rsaKeySize);
string publicKey = rsa.ToXmlString(false);
if (verbose)
{
Console.WriteLine("RSA Public Key: " + publicKey + "\n");
}
string message = sessionId_ + random2 + publicKey;
streamWriter.WriteLine(passAES.Encrypt(HashedMessage.FormMessage(message))); // 3
streamWriter.Flush();
hashedMessage = new HashedMessage(passAES.Decrypt(streamReader.ReadLine())); //4
messageRecieved = hashedMessage.Message; //4
if (messageRecieved.Substring(0, SESSION_ID_LENGTH) != others_sessionID)
{
return(false);
}
string restOfMessage = messageRecieved.Substring(SESSION_ID_LENGTH);
byte[] sessionKey = rsa.Decrypt(Convert.FromBase64String(restOfMessage), true);
sessionAES = new SimpleAES(sessionKey);
sessionAES.verbose = verbose;
if (verbose)
{
Console.WriteLine("SessionKey: " + Convert.ToBase64String(sessionAES.key));
}
}
return(true);
}
