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Security Fundamentals & Crypto · Advanced

Shamir's Secret Sharing (SSS)

Algorithm that splits a secret into N shares where any threshold of M shares can reconstruct it.

Definition

Developed by Adi Shamir in 1979, the scheme uses polynomial interpolation so fewer than M shares reveal nothing about the secret. It implements M-of-N control for master keys and recovery. HashiCorp Vault uses it by default to split the unseal key.

Example

vault operator init -key-shares=5 -key-threshold=3 creates five unseal key shares needing three to unseal.

Exam tip

Fewer than the threshold of shares reveal zero information about the secret.

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