@pbnjam/bandersnatch

Bandersnatch elliptic curve primitives built on top of @noble/curves.

This package provides:

• A Bandersnatch curve instance (Bandersnatch) configured with the official parameters.
• A high-level helper class (BandersnatchCurve) for point operations and arkworks-compatible serialization.
• Public curve parameters (BANDERSNATCH_PARAMS).

Note: VRF functionality and Elligator2 hash-to-curve are implemented in @pbnjam/bandersnatch-vrf.

Installation

This repository uses Bun workspaces. From the monorepo root, install deps once:

bun install

Within another workspace package, add a dependency on @pbnjam/bandersnatch via the workspace tooling you use (Bun/npm/pnpm/yarn).

Usage

Import the public API

import { Bandersnatch, BandersnatchCurve, BANDERSNATCH_PARAMS } from '@pbnjam/bandersnatch'
import type { CurvePoint } from '@pbnjam/bandersnatch'

Work with points (high-level helpers)

BandersnatchCurve exposes common operations over Noble Bandersnatch points (EdwardsPoint from @noble/curves), such as:

• GENERATOR: the canonical generator point
• INFINITY: point at infinity (identity)
• add(P, Q), negate(P), scalarMultiply(P, k)

import { BandersnatchCurve } from '@pbnjam/bandersnatch'

const P = BandersnatchCurve.GENERATOR
const Q = BandersnatchCurve.scalarMultiply(P, 2n)
const R = BandersnatchCurve.add(P, Q)
const negR = BandersnatchCurve.negate(R)

// Access affine coordinates (BigInt) via Noble helpers
const { x, y } = R.toAffine()
void x
void y

Arkworks-compatible point serialization

The helper methods are intended to be compatible with arkworks’ Twisted Edwards compression format.

import { Bandersnatch, BandersnatchCurve } from '@pbnjam/bandersnatch'

// Noble point → compressed bytes (arkworks-compatible)
const noblePoint = Bandersnatch.BASE
const compressed = BandersnatchCurve.pointToBytes(noblePoint)

// Compressed bytes → Noble point (throws on invalid encoding)
const parsed = BandersnatchCurve.bytesToPoint(compressed)

Public API

Exports

From src/index.ts:

• BandersnatchCurve
• Bandersnatch
• BANDERSNATCH_PARAMS
• CurvePoint (type)

CurvePoint

CurvePoint is a simple structural representation used by some algorithms (notably @pbnjam/bandersnatch-vrf’s Elligator2 hash-to-curve helpers):

• x: bigint
• y: bigint
• isInfinity: boolean

Parameters

All protocol constants are defined in src/config.ts as BANDERSNATCH_PARAMS (field modulus, curve order, generator, coefficients, and related configuration used by dependent packages).

Development

From packages/bandersnatch:

bun run test

bun run build

Security & correctness notes

• BandersnatchCurve uses BigInt arithmetic and performs modular operations over the Bandersnatch field.
• When handling serialized points, treat all external inputs as untrusted and rely on parsing/validation helpers (avoid manual decoding).