How deadhand Works

The Problem: The Trust Paradox

When you die, your crypto dies with you—unless you've shared your seed phrase. But sharing creates risk:

• Share with family? They might steal it
• Use a lawyer? They don't understand crypto
• Use a service? You're trusting them with everything

This is the Trust Paradox: You need to share access, but sharing access is dangerous.

The Solution: Shamir's Secret Sharing

deadhand uses a cryptographic technique called Shamir's Secret Sharing (SSS), invented by Adi Shamir in 1979.

How SSS Works

Instead of storing your secret as a single piece of data, SSS splits it into multiple "shards" with a threshold scheme:

Secret → Split into N shards → Need K shards to recover (K ≤ N)

deadhand uses a 2-of-3 scheme: - 3 shards are created - Any 2 shards can recover the original - 1 shard alone reveals zero information

Mathematical Guarantee

This isn't just "hard to crack"—it's information-theoretically secure:

• With 1 shard, an attacker has infinite possible secrets
• No amount of computing power changes this
• It's not encryption that can be broken—it's math

The deadhand Architecture

┌─────────────────────────────────────────────────────────┐
│                    YOUR BROWSER                          │
│  ┌─────────────┐    ┌─────────────┐    ┌─────────────┐  │
│  │ Seed Phrase │ -> │ Shamir SSS  │ -> │  3 Shards   │  │
│  │ (plaintext) │    │ (JavaScript)│    │  A, B, C    │  │
│  └─────────────┘    └─────────────┘    └─────────────┘  │
│         ↓                                    ↓          │
│   Never leaves                         Distributed      │
│   your browser                                          │
└─────────────────────────────────────────────────────────┘
                              │
              ┌───────────────┼───────────────┐
              ↓               ↓               ↓
         ┌─────────┐    ┌─────────┐    ┌─────────┐
         │ Shard A │    │ Shard B │    │ Shard C │
         │   YOU   │    │  HEIR   │    │ SERVER  │
         └─────────┘    └─────────┘    └─────────┘

The Dead Man's Switch

Heartbeat System

1. Every 30 days: Server sends you an email
2. Click the link: Confirms you're alive, resets timer
3. Miss 3 checks: Switch triggers after 90 days

What Triggers Release?

Day 0    → Vault activated
Day 30   → Email #1 sent
Day 60   → Email #2 sent (if #1 missed)
Day 90   → Email #3 sent (if #2 missed)
Day 91+  → Shard C emailed to beneficiary

Why 90 Days?

• Short enough to be useful
• Long enough to account for vacation, hospital, etc.
• Can be customized in future versions

Recovery Process

When the switch triggers:

1. Beneficiary receives email with Shard C
2. They already have Shard B (the printed PDF)
3. They visit deadhand's recovery page
4. They enter both shards
5. Original seed phrase is reconstructed
6. They can now access the wallet

Trust Model Summary

The only way to recover is with 2 shards—exactly as designed.