A secure, chunk-based file transfer tool written in C.
ChunkNet is a file transfer tool that splits files into fixed-size chunks, encrypts everything with modern AEAD ciphers, and verifies integrity at both chunk and file levels.
- Chunk-based transmission: Files are split into 256KB chunks for efficient transfer
- End-to-end encryption: X25519 key exchange with ChaCha20-Poly1305 or AES-256-GCM
- Integrity verification: SHA-256 checksums per-chunk and whole-file hash validation
- Simple CLI: Easy-to-use send and receive commands
- C99 compatible compiler (gcc, clang)
- libsodium (
brew install libsodiumon macOS,apt install libsodium-devon Debian/Ubuntu) - POSIX-compatible system (Linux, macOS, BSD)
make # Build the project
make test # Run all tests (88 tests)
make clean # Remove object files
make re # Rebuild from scratchReceive a file:
# Start receiver (waits for incoming connection)
./chunknet receive
# Or specify a custom port
./chunknet receive --port 8080Send a file:
# Send a file to a receiver
./chunknet send 192.168.1.100 document.pdf
# Or specify a custom port
./chunknet send 192.168.1.100 document.pdf --port 8080Example session:
# Terminal 1 - Receiver
$ ./chunknet receive
Initializing receiver...
Listening on port 4200...
Waiting for connection...
Connection accepted. Receiving file...
File received and verified successfully!
# Terminal 2 - Sender
$ ./chunknet send 127.0.0.1 myfile.zip
Initializing sender...
Connecting to 127.0.0.1:4200...
Connected. Sending file: myfile.zip
File sent successfully!ChunkNet uses a binary protocol with a 12-byte header and length-prefixed messages. The transfer flow:
┌────────┐ ┌──────────┐
│ Sender │ │ Receiver │
└───┬────┘ └────┬─────┘
│ │
│ ─────────── HELLO ──────────────────► │
│ ◄────────── HELLO_ACK ─────────────── │
│ │
│ ─────────── KEY_EXCHANGE ───────────► │
│ ◄────────── KEY_EXCHANGE_ACK ──────── │
│ │
│ ══════ [Encrypted from here] ═══════ │
│ │
│ ─────────── FILE_INFO ──────────────► │
│ ◄────────── FILE_INFO_ACK ─────────── │
│ │
│ ─────────── CHUNK [0] ──────────────► │
│ ◄────────── CHUNK_ACK [0] ─────────── │
│ ─────────── CHUNK [1] ──────────────► │
│ ◄────────── CHUNK_ACK [1] ─────────── │
│ ... │
│ ─────────── TRANSFER_COMPLETE ──────► │
│ ◄────────── TRANSFER_VERIFIED ─────── │
│ │
For the complete protocol specification, see docs/PROTOCOL.md.
src/
├── main.c # Entry point, CLI dispatch
├── cli/
│ ├── cli.h # CLI types
│ └── parse.c # Argument parsing
├── protocol/
│ ├── message.h/c # Message serialization (12-byte header, all payloads)
│ ├── sender.h/c # Sender state machine
│ └── receiver.h/c # Receiver state machine
├── network/
│ └── socket.h/c # TCP socket abstraction
├── crypto/
│ └── crypto.h/c # libsodium wrappers (X25519, ChaCha20, SHA-256, HKDF)
├── file/
│ └── file.h/c # File reading, writing, chunking, hashing
├── common/
│ └── dbgprintf.h/c # Debug utilities
└── const.h # Protocol constants
ChunkNet has comprehensive test coverage with 88 unit and integration tests:
make test| Test Suite | Tests | Description |
|---|---|---|
| parse_receive | 16 | CLI parsing for receive command |
| parse_send | 22 | CLI parsing for send command |
| message | 13 | Protocol message serialization |
| socket | 7 | TCP socket operations |
| crypto | 13 | Cryptographic operations |
| file | 14 | File I/O and chunking |
| transfer | 3 | End-to-end transfer integration |
- X25519 Key Exchange: Ephemeral ECDH for forward secrecy
- ChaCha20-Poly1305: Authenticated encryption (AES-256-GCM also supported)
- HKDF-SHA256: Secure session key derivation
- SHA-256: Integrity verification at chunk and file level
- Constant-time operations: Via libsodium to prevent timing attacks
| Name | Value | Description |
|---|---|---|
DEFAULT_PORT |
4200 | Default listening port |
CHUNK_SIZE |
256 KB | Size of each file chunk |
MAGIC_NUMBER |
0x434E4554 | Protocol identifier ("CNET") |
MIT License