Building Rock-Solid Encrypted Applications
summary
A live chat app is built step‑by‑step and works in demos: plain text → server‑side symmetric → end-to-end encryption with per‑device public/private keys → multi‑recipient encryption → ephemeral keys for perfect forward secrecy and one‑minute expiry. Device linking uses a QR code + temporary key over a websocket for provisioning. Diffie‑Hellman is used to derive symmetric session keys so ciphertext stays compact; reencryption lets new members access history. Signal’s user base jumped 4,000% after WhatsApp changes.
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chapters (18)
- 0:00Introduction
- 3:54Encryption matters
- 7:19Chat app security flaws
- 10:25Symmetric encryption demo
- 13:16End-to-end encryption
- 16:24E2E encryption demo
- 21:21Multi-recipient encryption
- 28:51Ephemeral keys for PFS
- 31:40Ephemeral keys demo
- 40:27Key rotation strategies
- 48:08Multi-device key management
- 51:58Device linking with QR
- 55:26Scalability with public key
- 57:12Diffie-Hellman exchange
- 1:00:26Symmetric encryption with DH
- 1:02:13Metadata attacks
- 1:05:00Protecting against metadata
- 1:06:01Summary
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