This project implements a secure, multi-client communication system in C++ using modern cryptographic algorithms: ChaCha20-Poly1305 for authenticated encryption and X25519 for secure key exchange. It allows simultaneous connections from multiple clients to a central server, enabling encrypted real-time messaging and file transfer with built-in logging and full control from the server side.
Designed as a robust, modular, and real-world secure communication platform.
Here’s a live demonstration showing:
- The server running and accepting connections.
- 3 clients connected, each with a unique ID.
- Using the
listcommand to view connected clients. - Sending a
broadcastmessage to all clients at once.
- ✅ End-to-end encryption using ChaCha20-Poly1305 (AEAD).
- ✅ Ephemeral session keys via X25519 ECDH key exchange.
- ✅ Multiclient support with unique session per client.
- ✅ Encrypted file transfer including metadata (name, size).
- ✅ Binary communication protocol (type + length + data).
- ✅ XML-based configuration for IP/PORT.
- ✅ Custom command interface for both client and server.
- ✅ Logging system for all communications.
- ✅ Safe packet reconstruction before decryption.
+------------+ +-------------+
| Client 1 | <--+ +->| Server |<--+--> Client N
+------------+ | | +-------------+ |
| ChaCha20 |<---+ +--| X25519 | +-> Logger
+------------+ +-------------+
- Each client initiates connection and performs ECDH handshake.
- A unique symmetric session key is derived.
- All communication is encrypted + authenticated using ChaCha20-Poly1305.
- Server handles multiple clients concurrently with threading.
graph LR
A[ChaCha20-Poly1305-X25519/] --> A1[README.md]
A --> A2[LICENSE]
A --> A3[client.cpp]
A --> A4[server.cpp]
A --> A5[common_crypto.h]
A --> A6[logger.h]
A --> A7[tinyxml2.cpp/.h]
A --> B[logs/]
B --> B1[communications_history.log]
A --> C[bin/]
C --> C1[client.exe]
C --> C2[server.exe]
A --> D[public/]
D --> D1[COMPILATION.md]
D --> D2[images/]
D2 --> D3[demo_execution.png]
A --> E[received_files/]
A --> F[src/]
F --> F1[client.bat]
F --> F2[server.bat]
F --> F3[client.xml]
F --> F4[server.xml]
- C++17 or higher
- OpenSSL (1.1.1+)
- TinyXML2
- g++ (MinGW-w64) for Windows
g++ client.cpp tinyxml2.cpp -lws2_32 -lssl -lcrypto -o bin/client.exe
g++ server.cpp tinyxml2.cpp -lws2_32 -lssl -lcrypto -o bin/server.exeEnsure that the DLLs from OpenSSL are accessible at runtime (libssl, libcrypto).
Use the .bat scripts to run:
src/client.bat
src/server.batThey load config from:
client.xmlfor the clientserver.xmlfor the server
Each file contains:
<config>
<ip>127.0.0.1</ip>
<port>40000</port>
</config>- X25519: Each connection uses ephemeral keys to derive a shared session key securely.
- ChaCha20-Poly1305:
- 256-bit key
- 96-bit nonce
- 128-bit authentication tag
- Nonces and keys are generated using secure RNG (OpenSSL).
Every message is sent in this format:
[ 4 bytes length ] [ 1 byte type ] [ encrypted content ] [ 16 bytes tag ]
- Types:
0x01Text message0xAAEncrypted file with metadata0x04Broadcast message0xFFExit / shutdown
- Command:
file <path> - Payload structure (encrypted):
[4 bytes client ID][4 bytes name_len][filename][8 bytes size][file_data]
- Files are saved on the server in
received_files/ - All parts (name, size, content) are encrypted.
- Client connects and receives server public key
- Client sends its public key
- Server derives shared key and sends nonce
- Communication begins: encrypted messages/files
- Messages are reconstructed based on length before decryption
- Each client gets a unique 4-digit ID
- Server operator can:
- List connected clients:
list - Send private messages:
send <id> <msg> - Broadcast to all:
broadcast <msg>
- List connected clients:
- Keys are ephemeral and regenerated on every connection
- No key is stored on disk
- Each session is uniquely encrypted
- AEAD cipher ensures confidentiality + authenticity
- No plaintext metadata transmitted
- Per-client encryption avoids shared state
- Secure random generation for all nonces and keypairs
- Logs never store plaintext content
mario@server:~$ list
[*] Connected clients:
ID: 1032
ID: 4821
mario@server:~$ send 1032 Hola, cliente 1032
[>] Message sent to Client 1032
mario@client[1032]:~$ file C:/Users/user/Desktop/test.pdf
[*] Archivo enviado: test.pdf (14358 bytes)Logs are automatically stored with timestamp, source, and message. Sample:
[2025-04-16 00:01:01.646] [Servidor 1842] Cliente conectado
[2025-04-16 00:01:08.984] [Servidor 7935] Cliente conectado
[2025-04-16 00:01:12.122] [Servidor 6263] Cliente conectado
[2025-04-16 00:03:20.371] [Broadcast 6263] Hola a todos los clientes
[2025-04-16 00:03:20.371] [Broadcast 7935] Hola a todos los clientes
[2025-04-16 00:03:20.371] [Broadcast 1842] Hola a todos los clientes
[2025-04-16 00:03:20.372] [Servidor -1] Broadcast: Hola a todos los clientes
[2025-04-16 00:03:45.434] [Servidor 7935] Hola cliente individual
[2025-04-16 00:04:11.820] [Cliente 1842] Hola Servidor, soy un Cliente
[2025-04-16 00:04:46.816] [Cliente 6263] Oye Servidor, te voy a enviar un NFT
[2025-04-16 00:05:42.763] [Cliente 6263] Archivo recibido: NFT_V5.jpg (72523 bytes)
[2025-04-16 00:06:09.480] [Servidor 6263] Recibido el NFT, muchas gracias
[2025-04-16 00:06:17.591] [Cliente 7935] Adios
[2025-04-16 00:06:20.620] [Servidor 7935] Cliente desconectado
[2025-04-16 00:06:35.365] [Cliente 6263] Tengo que irme
[2025-04-16 00:06:37.895] [Servidor 6263] Cliente desconectado
[2025-04-16 00:07:00.628] [Servidor -1] Server terminated via 'exit' command.
📄 Full log file available here: communications_history.log
This project is licensed under a custom educational license.
See the full license here: LICENSE
Developed by @marichu_kt
Official Repository: ChaCha20-Poly1305-X25519