guptachitra — the hidden picture
Image Steganography
Bury a secret message, or a whole file — a PDF, a spreadsheet, even another photo — deep inside an ordinary picture. It is encrypted with a key only you know, then scattered bit by bit through the image's own colour data. The picture looks exactly the same. Only this page, and only your key, can bring the secret back.
How it actually works
- 1. Your message or file is encrypted right here in your browser with AES-256-GCM. The key is stretched from your secret phrase through 200,000 rounds of PBKDF2, so guessing it is punishing work.
- 2. Every pixel is three hex numbers — red, green, blue. The encrypted bytes are written into the very last bit of those numbers. A red of A4 might become A5. Your eye cannot see a difference of one in 255.
- 3. When you hide something large, like a whole file or a photo inside a photo, the tool automatically uses two or three low bits per colour instead of one, so it still fits. It always uses the fewest it can.
- 4. The bit positions come from a random walk seeded by your key itself, so without the key you cannot even find where the data sits, never mind decrypt it. Nothing is uploaded — everything happens on your own device.
Your image and files never leave your device. Site activity from this tool, including submitted text and file names, is recorded by the site owner for security and abuse prevention. Please do not use it for anything unlawful, and do not treat it as a substitute for proper end-to-end encrypted messaging.