What is Shamir's Secret Sharing?
Split a secret into N pieces — require any K to reconstruct it.
Definition
Shamir's Secret Sharing (SSS) is a cryptographic algorithm invented by Adi Shamir in 1979. It splits a secret (such as an encryption key) into N shares, distributed among N parties. The secret can only be reconstructed when at least K of those N shares are combined — where K is a threshold you define. No single share reveals any information about the secret.
How It Works
For example, in a 2-of-3 scheme: the secret is split into 3 shares. Any 2 of the 3 holders can reconstruct the secret. One holder alone learns nothing. This is mathematically guaranteed — not just a policy. The scheme is based on polynomial interpolation over a finite field, meaning it is information-theoretically secure. Even an attacker with K-1 shares gains zero information about the secret.
How VaultPass Uses This
VaultPass uses a 2-of-3 Shamir scheme for vault key distribution. Your vault encryption key is split into three shards: one held by you (the owner), one designated to your heir, and one held by a VaultPass guardian node. Any two parties can reconstruct the key. This means: (1) VaultPass alone cannot decrypt your vault, (2) your heir alone cannot decrypt it until the switch fires, (3) you retain full control while alive.
Common Questions
What happens if one shard holder loses their shard?
With a 2-of-3 scheme, you only need any two of the three shards. Losing one does not prevent recovery — the remaining two are sufficient.
Is Shamir's Secret Sharing used by governments and banks?
Yes. Shamir's Secret Sharing is used in hardware security modules (HSMs), certificate authorities, and military systems worldwide. It is one of the most proven cryptographic primitives in existence.