Secrets Sharing

A TypeScript library for Shamir's Secret Sharing using Buffers instead of strings.

Inspired by grempe/secrets.js, but operates on Buffer objects for native binary data support.

Features

• Split secrets into shares using Shamir's threshold scheme
• Reconstruct secrets from shares
• Generate new shares from existing ones without knowing the secret
• Works with arbitrary binary data (Buffers)
• Configurable bit-width for the finite field (3–20 bits)
• Pluggable RNG
• Zero dependencies

Installation

npm install secrets-sharing

Usage

import { share, combine } from 'secrets-sharing';

const secret = Buffer.from('my super secret data');

// Split into 5 shares, requiring any 3 to reconstruct
const shares = share(secret, 5, 3);

// Reconstruct from any 3 shares
const recovered = combine(shares.slice(0, 3));
console.log(recovered.toString()); // 'my super secret data'

API

share(secretBuffer, numShares, threshold, padLength?)

Split a secret Buffer into shares using Shamir's threshold secret sharing.

| Parameter | Type | Description | |---|---|---| | secretBuffer | Buffer | The secret to split. | | numShares | number | Total shares to produce (2 to config.max). | | threshold | number | Minimum shares required to reconstruct (2 to numShares). | | padLength | number | Zero-pad the binary secret to a multiple of this many bits before splitting. Defaults to 128. Must be 0–1024. |

Returns: Buffer[] — an array of share Buffers.

combine(shares, at?)

Reconstruct a secret Buffer from an array of share Buffers.

| Parameter | Type | Description | |---|---|---| | shares | Buffer[] | Array of share Buffers (must meet the threshold count). | | at | number | Evaluates the polynomial at this x value instead of 0. Defaults to 0. Used internally by newShare. |

Returns: Buffer — the reconstructed secret.

newShare(id, shares)

Generate a new share with the given numeric id from existing shares, without reconstructing the secret.

| Parameter | Type | Description | |---|---|---| | id | number | Share id, an integer in [1, config.max]. | | shares | Buffer[] | At least threshold existing share Buffers. |

Returns: Buffer — a new share Buffer for the requested id.

init(bits?)

Initialize (or reinitialize) the finite field used for sharing. Called automatically on import with 8 bits.

| Parameter | Type | Description | |---|---|---| | bits | number | Bit-width for the field (3–20). Defaults to 8. |

setRNG(rng)

Provide a custom random number generator. By default the library uses Math.random.

| Parameter | Type | Description | |---|---|---| | rng | (() => number) \| null | A function returning an integer in [0, config.max], or null to reset to the default. |

getConfig()

Return the current library configuration.

Returns: { bits: number; radix: number; maxShares: number }

extractShareComponents(shareBuffer)

Extract the components of a share Buffer.

| Parameter | Type | Description | |---|---|---| | shareBuffer | Buffer | A share Buffer produced by share() or newShare(). |

Returns: { bits: number; id: number; data: string } — where data is the hex payload.

shareBufferToString(shareBuffer)

Convert a share Buffer to its ASCII string representation.

Returns: string

shareStringToBuffer(shareString)

Convert an ASCII share string back to a Buffer.

Returns: Buffer

utf16beFromString(str)

Encode a JS string into a UTF-16BE Buffer with reversed code-unit ordering (matches the secrets.js str2hex convention).

Returns: Buffer

utf16beToString(buf)

Decode a UTF-16BE Buffer (with reversed code-unit ordering) back into a JS string.

Returns: string

Inspiration

Based on the well-known secrets.js library, adapted to work natively with Buffer objects and binary data.

License

ISC