Secret Sharing: Real World Examples

TL;DR

Yes! Secret sharing isn’t just theory. It’s used in things like key management for critical infrastructure, secure voting systems, and even protecting digital assets. This guide explains how it works in practice with examples.

What is Secret Sharing?

Secret sharing breaks a secret into multiple ‘shares’. No single share reveals the original secret. You need a threshold number of shares to reconstruct it. A common scheme is Shamir’s Secret Sharing, but others exist.

Real-World Implementations

1. Key Management Systems (KMS): This is probably the most widespread use.
   • How it works: Instead of one person holding a master encryption key, it’s split into shares distributed amongst trusted administrators.
   • Example: A data centre might have 5 admins each with a share. 3 shares are needed to unlock the key and decrypt sensitive data. This prevents a single compromised admin account from exposing everything.
2. Secure Voting Systems:
   • How it works: Each vote is encrypted, then split into shares. Shares are distributed to different servers/authorities. Reconstruction happens only after the voting period closes and requires a majority of shares.
   • Example: Helios Voting System (open-source) uses secret sharing for tallying votes securely. It prevents manipulation by ensuring no single entity can alter the results.
3. Digital Asset Protection (e.g., Cryptocurrency Wallets):
   • How it works: A cryptocurrency wallet’s private key is split into shares. This protects against loss or theft of a single device/key component.
   • Example: Multi-signature wallets often use secret sharing principles (though not always strictly Shamir’s). You need approvals from multiple devices to authorise transactions.
4. Protecting Database Credentials:
   • How it works: The database password or connection string is split into shares and stored separately.
   • Example: A company might store shares in different cloud providers, reducing the risk of a single provider breach exposing all credentials.

Tools & Libraries

You don’t usually build secret sharing from scratch; you use existing tools.

1. Shamir Secret Sharing (Python): The sss library is popular.

   pip install sss

   # Example: Split a secret into shares
   import sss
   secret = b'MySuperSecretPassword'
   num_shares = 5
   threshold = 3
   shares = sss.split(secret, num_shares, threshold)
   print(shares)

2. Keycloak: An open-source Identity and Access Management solution that can integrate with secret sharing mechanisms for key management.
3. HashiCorp Vault: A secrets management tool offering features like Shamir’s Secret Sharing for protecting dynamic credentials.

Practical Considerations

1. Share Security: The security of the shares is paramount. Protect them as you would any other sensitive data (encryption, access control).
2. Threshold Selection: Choose a threshold that balances security and usability. A higher threshold increases security but requires more parties to cooperate for reconstruction.
3. Auditing: Keep logs of share creation, distribution, and reconstruction attempts.
4. Loss/Compromise Recovery: Have procedures in place for dealing with lost or compromised shares (e.g., re-splitting the secret).