TCrypto — Hybrid Image Encryption (RSA + AES)

Requirements

• GCC (MinGW or WSL)
• OpenSSL (libssl, libcrypto)
• Python 3 with numpy, matplotlib, pillow (for analysis only)

Quick Start

# Build and run all 3 encryption tasks (Raw RSA, RSA+OAEP, Hybrid AES)
make run

# Build and run the custom-key demo
make test

# Clean build artifacts
make clean

What make run Does

Reads an input image, generates a 1024-bit RSA key, then runs:

1. Task 1 — Raw RSA block-by-block encryption/decryption
2. Task 2 — RSA + OAEP (semantic security)
3. Task 3 — Hybrid: RSA+OAEP wraps a random AES-256 key, AES-CBC encrypts the image

Both PNG (file bytes) and BMP (raw pixels) are processed. Results go to output_*/:

• performance.csv — timing data
• bmp_task*_encrypted.bmp — encrypted images for visual inspection
• bmp_task*_decrypted.bmp — decrypted roundtrip verification

Note: Tasks 1–2 on large images are slow (minutes to hours). Task 3 finishes in milliseconds.

What make test Does

Generates an RSA key, exports the primes as hex strings, rebuilds the key from those hex strings using rsa_key_from_hex(), and verifies encryption/decryption still works. Demonstrates how to use a custom key instead of generating one.

Analysis (Python)

After make run, generate security metrics and plots:

python scripts/analyze.py output_colored
python scripts/analyze.py output_blackandwhite

Produces metrics.csv and plots/ (histograms, entropy, correlation, etc.).

Report

typst compile --root . docs/report.typ

Project Structure

src/
  bignum.c      — Arbitrary-precision arithmetic (hand-implemented)
  rsa.c         — RSA keygen, encrypt/decrypt with CRT
  oaep.c        — OAEP padding (SHA-256 + MGF1)
  aes_cbc.c     — AES-256-CBC wrapper (OpenSSL)
  bmp_io.c      — BMP image reader/writer
  main.c        — Benchmark runner (make run)
  demo_custom_key.c — Custom key demo (make test)

include/        — Header files for each module
scripts/        — Python analysis scripts
docs/           — Typst report source