ecc-jsbn/index.js

ECC JS code based on JSBN

"use strict";

const crypto = require("crypto");
const { BigInteger } = require("jsbn");

exports.ECCurves = require("./lib/sec.js");

// zero prepad
function unstupid(hex, len) {
  return hex.length >= len ? hex : unstupid("0" + hex, len);
}

exports.ECKey = function(curve, key, isPublic) {
  var priv;
  var c = curve();
  var n = c.getN();
  var bytes = Math.floor(n.bitLength() / 8);

  if (key) {
    if (isPublic) {
      var curve = c.getCurve();
      //      var x = key.slice(1,bytes+1); // skip the 04 for uncompressed format
      //      var y = key.slice(bytes+1);
      //      this.P = new ECPointFp(curve,
      //        curve.fromBigInteger(new BigInteger(x.toString("hex"), 16)),
      //        curve.fromBigInteger(new BigInteger(y.toString("hex"), 16)));
      this.P = curve.decodePointHex(key.toString("hex"));
    } else {
      if (key.length != bytes) return false;
      priv = new BigInteger(key.toString("hex"), 16);
    }
  } else {
    var n1 = n.subtract(BigInteger.ONE);
    var r = new BigInteger(crypto.randomBytes(n.bitLength()));
    priv = r.mod(n1).add(BigInteger.ONE);
    this.P = c.getG().multiply(priv);
  }
  if (this.P) {
    //  var pubhex = unstupid(this.P.getX().toBigInteger().toString(16),bytes*2)+unstupid(this.P.getY().toBigInteger().toString(16),bytes*2);
    //  this.PublicKey = Buffer.from("04"+pubhex,"hex");
    this.PublicKey = Buffer.from(
      c.getCurve().encodeCompressedPointHex(this.P),
      "hex"
    );
  }
  if (priv) {
    this.PrivateKey = Buffer.from(
      unstupid(priv.toString(16), bytes * 2),
      "hex"
    );
    this.deriveSharedSecret = function(key) {
      if (!key || !key.P) return false;
      var S = key.P.multiply(priv);
      return Buffer.from(
        unstupid(
          S.getX()
            .toBigInteger()
            .toString(16),
          bytes * 2
        ),
        "hex"
      );
    };
  }
};