awaforge

bn

Apache-2.0Release 1L3

Big Number — arbitrary-precision integer arithmetic (SJCL-derived, BSD-2-Clause; see provenance) for ECDSA / RSA.

Module bn | Source packages/front/fw/src/crypto/utils/bn.js | Deps bitArray, random | Worker-safe yes

Representation: array of 24-bit limbs. Underlying ecc, rsa, rsaKeygen.

Resolve

const bn = runtime.resolve('bn');
// Returns: BN constructor + statics

API (excerpt)

Method Signature Returns
bn.fromBits(bits) / .toBits() — bitArray ↔ BN conversion
new bn(hex) / .toHex() (hex: string) / () => string Construct from hex string '0x…' (or number) ↔ hex serialisation '0x…'
add / sub / mul / mod / mulmod / power / powermod — Arithmetic
inverseMod(p) — Modular inverse (extended Euclidean)
equals(other) — Comparison (constant-time with same-limb-length)

API note: the hex method is named toHex() and not toString(). Object.prototype.toString is frozen by sanity/base.js; assigning Bn.prototype.toString would raise TypeError: Cannot assign to read only property 'toString'. All BN ↔ hex conversions go through toHex / the constructor.

Examples

const bn = fw.runtime.resolve('bn');
const a = new bn('0x1234');
const b = new bn('0xabcd');
const c = a.mulmod(b, new bn('0xffff'));   // (a*b) mod 0xffff

Worker Usage

const worker = fw.createWorker(
    function ({ libs, args }) {
        const a = new libs.bn(args[0]);
        self.postMessage(a.power(args[1]).toHex());
    },
    { dependencies: ['bn'], args: ['0x1234', 5] }
);

Notes

  • 24-bit limbs: trade-off inherited from the SJCL-derived design, for IEEE-754 precision + JS performance.
  • powermod: square-and-multiply with k-ary window (~O(bitLen) modmult).
  • equals: constant-time when BNs have the same limb length (prefer .normalize() before security-critical comparisons).

See also