## Title Show HN: TimeSeal – Cryptographic time-locked vaults with Dead Man's Switch

## Post Text

I built TimeSeal to solve a problem: most "future message" apps rely on trust. TimeSeal uses split-key cryptography to make early access mathematically impossible.

*How it works:*

Your browser generates two random AES-GCM-256 keys. Key A stays in the URL hash (never sent to server). Key B goes to Cloudflare Workers. The server refuses to release Key B until the unlock time. Without both keys, decryption is impossible—even for me.

*Three modes:*

1. *Timed Release* - Opens at exact future date (product launches, birthday messages) 2. *Dead Man's Switch* - Auto-unlocks if you stop checking in (crypto inheritance, whistleblower insurance) 3. *Ephemeral* - Self-destructs after N views (one-time passwords, confidential sharing)

*Architecture highlights:*

- Triple-layer encryption (client-side AES-GCM + server-side key encryption + master key) - Split-key design: no single party can decrypt early - Server-side time enforcement (client clock is irrelevant) - Cloudflare Workers + D1 database (edge-native, globally distributed) - Replay attack prevention with nonce-based pulse tokens - Rate limiting via SHA-256 browser fingerprinting - Open source (BSL license, converts to Apache 2.0 in 4 years)

*Security model:*

Even with full database access, an attacker cannot decrypt without: - Key A (in URL hash, never transmitted) - Master encryption key (environment secret) - Both keys combined

The server enforces time-locks via Cloudflare's NTP-synchronized infrastructure. No root access = no time manipulation.

*Use cases I didn't expect:*

- Estate planning (crypto seed phrases that unlock after 30 days of silence) - Journalist insurance (evidence auto-releases if arrested) - Marketing stunts (countdown timers for product drops) - Legal holds (contracts that activate on settlement date)

Live demo: https://timeseal.online

Source: https://github.com/teycir/timeseal

Docs cover threat model, attack scenarios, self-hosting, and trust assumptions. Happy to answer questions about the crypto, architecture, or edge cases.

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