Building a Privacy-First URL Shortener on Blockchain

Description and use

A privacy‑first URL shortener that encrypts links client‑side, stores ciphertext on the Cronos blockchain, and decrypts locally in the browser, eliminating server‑side visibility and centralized data storage.

Problem

Traditional URL shorteners log user data, track browsing patterns, and sell data, creating privacy risks and a single point of failure.

Outcome

The system provides a privacy‑first URL shortener where the server never sees the destination URL, no centralized database exists, and data is stored immutably on a blockchain, reducing hacking and censorship risks.

Workflow

• 1. User enters a URL in the client UI.
• 2. Client generates a random IV and AES‑GCM key using Web Crypto API.
• 3. Client encrypts the URL buffer with the key and IV.
• 4. Client sends the ciphertext to a Cloudflare Worker endpoint.
• 5. Worker writes the ciphertext to the Cronos blockchain via a transaction.
• 6. Worker returns a short code (hash of transaction or stored key).
• 7. User shares the short link (cryptly.workers.dev/<code>).
• 8. When the link is visited, the browser fetches the ciphertext from the blockchain via the Worker.
• 9. Browser decrypts the ciphertext locally with the stored key and IV.
• 10. Browser redirects to the original destination URL without exposing it to any server.

Evidence

Encrypted URL stored on Cronos blockchain

Source

Server never sees destination

Source