🔐 CN Secure File Transfer

This project is a Computer Networks (CN) course project that implements secure file transfer between machines over TCP with AES-based encryption.

Future Work Roadmap

🔐 Security Upgrades (High Impact)

• ✅ Add message authentication (MAC verification)

  • Explicitly verify AES-EAX authentication tags instead of only decrypting.
  • Reject tampered or incomplete files automatically.

• ✅ Use password confirmation handshake

  • Perform a small encrypted challenge-response before sending full file.
  • Prevent wasting bandwidth on wrong passwords.

• ✅ Implement replay-attack protection

  • Add per-session IDs or timestamps.
  • Reject reused nonces or duplicated sessions.

• ✅ Rate-limit authentication attempts

  • Prevent brute-forcing the preset authentication code.

🌐 Networking Enhancements

• ✅ Support multiple concurrent clients

  • Use threading or asyncio on the receiver side.
  • Handle each client in an isolated session.

• ✅ Chunk-based streaming encryption

  • Encrypt/send files in chunks instead of loading entire file into memory.
  • Enable large file support and lower RAM usage.

• ✅ Resume interrupted transfers

  • Track byte offsets with chunk manifests.
  • Use receiver-side bitmaps so the sender resumes only missing chunks.

• ✅ Add configurable socket timeouts

  • Prevent hanging connections.

🧾 Protocol & Architecture Improvements

• ✅ Define a formal application-layer protocol

  • Message types: AUTH, METADATA, DATA, ACK, ERROR.
  • Version the protocol (for example CNFT/1.0).

• ✅ Add integrity verification summary

  • Send SHA-256 hash of original file.
  • Verify hash after decryption.

• ✅ Introduce session keys

  • Derive one session key once.
  • Derive per-file keys from it (HKDF-style design).

🧑‍💻 Usability & UX Improvements

• CLI flags instead of interactive input

  • Example flags: --host, --port, --outdir, --file.
  • Make scripts automation-friendly.

• ✅ Progress reporting on both sides

  • Sender shows live tqdm progress bar.
  • Receiver should show live progress too.

• Transfer summary report

  • Include file size, duration, throughput, and encryption mode.

• Structured logging

  • Replace print statements with logging levels (INFO, WARN, ERROR).

📦 Engineering & Code Quality

• Split crypto, networking, and UI into separate modules

  • Example modules: crypto.py, protocol.py, network.py.

• Add unit tests for crypto and protocol logic

  • Key derivation consistency tests.
  • Metadata parsing correctness tests.

• Add requirements.txt and Makefile

  • Improve setup and reproducibility.

• Add type hints and docstrings

  • Improve maintainability and interview-readiness.

🔄 Feature Extensions (Very Impressive)

• End-to-end public-key exchange

  • Use RSA or ECC to exchange AES keys securely.
  • Eliminate direct password sharing.

• Encrypted directory transfer

  • Recursively send folders.
  • Preserve folder structure and metadata.

• Basic access control

  • Authorized sender list or user accounts.

• Encrypted file storage on receiver

  • Keep files encrypted at rest.
  • Decrypt only on demand.

🧠 Academic / Resume-Level Enhancements

• Threat model documentation

  • Define attacker capabilities and defenses.

• Security comparison section

  • Compare this protocol with SCP/SFTP at a high level.

• Performance benchmarks

  • Measure throughput across multiple file sizes.

• Protocol diagram

  • Visualize handshake, key derivation, transfer, and verification phases.