Openus.SecureProtocol 8.1.4.1

Secure Protocol

Information

The project Secure Protocol's goal is to build a Simple, Secure, and Fast Transport Layer Module with C#.

Tech Stack

• O: Completed works
• ?: Need more check
• X: Have only plan

Secure Protocol Example and Architecture

• Assume algorithm set is follow that.
  • Symmetric key algorithm is using AES.
  • Asymmetric key algorithm is using RSA.
  • Hash and HMAC algorithm is using SHA256.

1st. Exchange AES Key & HMAC Key from RSA/TCP

• Assume that the RSA public key on the server is already guaranteed by other means.

• 🔑: AES_KEY + HMAC_KEY
  • ≓ Session Key for SP-AES
• 🔐: RSA(S_PUBLIC_KEY, 🔑)
  • ≓ RSA Encrypted session keys for SP-AES, and this can decrypt only Server
• 📜: HMAC(HMAC_KEY, 🔑)
  • ≓ Hashed message for initail authentication
• 🔏: SP-AES(AES_KEY, 📜)
  • ≓ AES Encrypted hashed message for initail authentication

2nd. SP-AES Packet Structure

The SP is Secure Protocol

SP-AES is using CBC, and over the TCP/UDP

• Define IV + AES(AES_KEY, NONCE + MSG_LENGTH + MSG) to α.
  • So, the α mean encrypted message part.
• Write SP-AES packet is only follow the structure that α + HMAC(HMAC_KEY, α)

More Structure Information

• Remember, in this case...
  • AES block size is 128 bits.
  • HMAC hashed data size is 256 bits.

+----------+--------------------------------------------+------------------------------------+
|    IV    |            AES Encrypted Message           |                HMAC                |
| 128 bits |                  128n bits                 |              256 bits              |
|          |+---------+------------+-------------------+|+----------+-----------------------+|
|          ||  Nonce  | MSG Length |      Message      |||    IV    | AES Encrypted Message ||
|          || 32 bits |  32 bits   | m bits(Z-Padding) ||| 128 bits |       128n bits       ||
|          |+---------+------------+-------------------+|+----------+-----------------------+|
+----------+--------------------------------------------+------------------------------------+

Provide from Structure

• Data Confidentiality through AES(CBC).
• Data Integrity and Authentication through HMAC.
• In now, has plan that provide simple Availability like support blacklist system.

• AES_KEY, HMAC_KEY generate and exchange in the before time(in RSA) during the secure session.
• IV is randomly generated for each communication.
• Use the NONCE increased by 1 ~ 5 from last used, using in each write.
  • When read, if the NONCE did not increase based on last read NONCE, it is judged as an incorrect packet.
  • So, the write NONCE and the read NONCE are separated.

3rd. Usage Example

Key Generator

/// You must have RSA key pair before communication.
/// Don't worry. We provide RSA key pair generator!

using Openus.SecureProtocol.Key.Asymmetric;

KeyPair pair = KeyPair.GenerateRSA();

pair.PublicKey.Save("key.pub");
pair.PrivateKey.Save("key.priv");

Secure TCP Server

/// This is the Server side.

using Openus.SecureProtocol.Key.Asymmetric;
using Openus.SecureProtocol.Secure.Algorithm;
using Openus.SecureProtocol.Transport.Tcp;
using System.Net;

/// Load Private key
PrivateKey privkey = PrivateKey.Load(Asymmetric.RSA, "key.priv");

/// Algorithm set to use
Set set = new Set()
{
    Asymmetric = Asymmetric.RSA,
    Symmetric = Symmetric.AES,
    Hash = Hash.SHA256,
};

TcpServer server = TcpServer.Create(IPEndPoint.Parse($"127.0.0.1:12345"), privkey, set);
server.Start();

TcpServer.Client accept = server.AcceptClient()!;

for (int i = 0; i < 100; i++)
{
    byte[] buffer = accept.Read();
    accept.Write(buffer);

    accept.FlushStream();
}

server.Stop();

Secure TCP Client

/// This is the Client side.

using Openus.SecureProtocol.Key.Asymmetric;
using Openus.SecureProtocol.Secure.Algorithm;
using Openus.SecureProtocol.Transport.Tcp;
using System.Net;

/// Load Public key
PublicKey pubkey = PublicKey.Load(Asymmetric.RSA, "key.pub");

/// Algorithm set to use
Set set = new Set()
{
    Asymmetric = Asymmetric.RSA,
    Symmetric = Symmetric.AES,
    Hash = Hash.SHA256,
};

TcpClient client = TcpClient.Create(pubkey, set);
client.InitialConnect(IPEndPoint.Parse($"127.0.0.1:12345"));

byte[] buffer = new byte[1024];
new Random().NextBytes(buffer);

byte[] check = (byte[])buffer.Clone();

for (int i = 0; i < 100; i++)
{
    client.Write(buffer);
    buffer = client.Read();

    client.FlushStream();
}

if (buffer.SequenceEqual(check) == false)
    throw new Exception("buffer is corrupted");

client.Close();

• This example is like repeated 100 times Ping-Pong, through RSA, SP-AES over the TCP.
• And last, the program check that message is corrupted.