Shardium

Trustless dead man's switch for crypto inheritance using Shamir's Secret Sharing

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The Problem

You die. Your crypto dies with you. Your family has no idea how to access it.

Traditional solutions require trusting someone with your seed phrase. That's not acceptable.

The Solution

Shardium uses Shamir's Secret Sharing to split your seed phrase into 3 shards. No single entity (including us) has the full key.

Inspired by @PixOnChain

Features

• Client-Side Encryption - Your seed phrase never leaves your browser unencrypted
• Shamir's Secret Sharing - Mathematically proven 2-of-3 threshold scheme
• Automated Dead Man's Switch - 30-day heartbeat checks, triggers after 90 days
• PDF Export - Print shards for physical backup
• Beneficiary System - Seamless crypto inheritance
• Zero Trust Architecture - Even we can't access your keys
• Fully Open Source - Audit the code yourself

How It Works

Shard Distribution

flowchart LR
    subgraph Browser["Client Browser"]
        SEED["Seed Phrase"]
        SPLIT["Shamir Split (2-of-3)"]
    end
    
    SEED --> SPLIT
    SPLIT --> A["Shard A<br/>User Keeps"]
    SPLIT --> B["Shard B<br/>Beneficiary"]
    SPLIT --> C["Shard C<br/>Server"]
    
    style SEED fill:#f59e0b,color:#000
    style A fill:#14b8a6,color:#000
    style B fill:#eab308,color:#000
    style C fill:#8b5cf6,color:#fff

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Dead Man's Switch Flow

sequenceDiagram
    participant U as User
    participant S as Shardium Server
    participant B as Beneficiary

    Note over U,S: Every 30 days
    S->>U: "Are you alive?" Email
    
    alt User Responds
        U->>S: Click heartbeat link
        S->>S: Reset 30-day timer
    else User Missing (90 days)
        S->>B: Email Shard C
        Note over B: Combines Shard B + C
        B->>B: Recovers Seed Phrase
    end

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Recovery Combinations

flowchart TB
    subgraph Valid["Valid Recovery (Any 2 Shards)"]
        AB["A + B"] --> RECOVER1["Seed Recovered"]
        AC["A + C"] --> RECOVER2["Seed Recovered"]
        BC["B + C"] --> RECOVER3["Seed Recovered"]
    end
    
    subgraph Invalid["Invalid (Single Shard = Zero Info)"]
        A1["A alone"] --> FAIL1["Nothing"]
        B1["B alone"] --> FAIL2["Nothing"]
        C1["C alone"] --> FAIL3["Nothing"]
    end
    
    style RECOVER1 fill:#22c55e,color:#000
    style RECOVER2 fill:#22c55e,color:#000
    style RECOVER3 fill:#22c55e,color:#000
    style FAIL1 fill:#ef4444,color:#fff
    style FAIL2 fill:#ef4444,color:#fff
    style FAIL3 fill:#ef4444,color:#fff

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Trust Model

Scenario	Outcome
Server hacked	Attacker has only Shard C → Useless
Beneficiary is malicious	They have only Shard B → Useless
You lose Shard A	Combine B + C → Still recoverable
You die	Server sends C to beneficiary → B + C = Recovery

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Tech Stack

• Backend: FastAPI, PostgreSQL, SQLAlchemy
• Frontend: HTML, TailwindCSS, HTMX
• Cryptography: secrets.js (Shamir's Secret Sharing) running in browser
• Hosting: Vercel

How to Run

1. Install dependencies:

   pip install -r requirements.txt

2. Run the server:

   python -m uvicorn app.main:app --reload --port 8000

3. Visit http://localhost:8000

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Security Note

This is an MVP/Proof of Concept. In a real production environment:

• Use HTTPS.
• Audit the secrets.js library.
• Ensure the database is secure.
• Use a real email provider (SendGrid/AWS SES) instead of the mock logger.

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Built by the Shardium Team

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Contributing

Contributions are welcome! Here's how you can help:

1. Fork the repository
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

Areas We Need Help With:

• Production-grade email integration
• Multi-language support
• Mobile app wrapper
• Hardware wallet integration
• Additional threshold schemes (3-of-5, etc.)

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License

This project is licensed under the MIT License - see below for details:

MIT License

Copyright (c) 2025 Shardium

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

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Star this repo if you find it useful!