@forgesworn/shamir-core

GF(256) Shamir's Secret Sharing for TypeScript. Split a secret into threshold-of-n shares and reconstruct from any threshold-sized subset.

Zero runtime dependencies. Pure TypeScript, Web Crypto only.

Install

npm install @forgesworn/shamir-core

Quick Start

import { splitSecret, reconstructSecret } from '@forgesworn/shamir-core';

// Split a 32-byte key into 5 shares, any 3 can reconstruct
const secret = crypto.getRandomValues(new Uint8Array(32));
const shares = splitSecret(secret, 3, 5);

// Reconstruct from any 3 shares
const recovered = reconstructSecret([shares[0], shares[2], shares[4]], 3);
// recovered is identical to secret

API

splitSecret(secret, threshold, shares)

Split a secret into Shamir shares.

| Parameter | Type | Description | |-----------|------|-------------| | secret | Uint8Array | The secret bytes to split (any length) | | threshold | number | Minimum shares needed to reconstruct (2--255) | | shares | number | Total shares to create (threshold--255) |

Returns ShamirShare[]. Each share has { id, threshold, data }.

reconstructSecret(shares, threshold)

Reconstruct a secret from shares using Lagrange interpolation.

| Parameter | Type | Description | |-----------|------|-------------| | shares | ShamirShare[] | At least threshold shares | | threshold | number | The threshold used during splitting |

Returns Uint8Array (the reconstructed secret).

Only the first threshold shares are used. Extra shares are ignored.

ShamirShare

interface ShamirShare {
  id: number;        // 1--255 (GF(256) evaluation point)
  threshold: number; // 2--255 (minimum shares to reconstruct)
  data: Uint8Array;  // Share data (same length as original secret)
}

Error Classes

• ShamirError -- base class
• ShamirValidationError -- invalid parameters
• ShamirCryptoError -- internal crypto errors

Why This Library

• Zero dependencies. No transitive supply chain. Only Web Crypto (crypto.getRandomValues).
• GF(256) log/exp table lookup. O(1) field multiplication, same polynomial as AES (0x11b).
• Memory zeroing. Polynomial coefficients are zeroed after use (defence-in-depth).
• Strict validation. Duplicate share IDs, threshold mismatches, and malformed inputs are caught with typed errors.
• No secret length limit. Split any size secret. The maths has no ceiling.
• TypeScript-first. Strict mode, noUncheckedIndexedAccess, full type declarations.

Ecosystem

| Package | Purpose | |---------|---------| | @forgesworn/shamir-words | BIP-39 word encoding for shares (depends on this package) | | dominion-protocol | Epoch-based encrypted access control (depends on this package) |

Licence

MIT