@stellot/crypto/lib/esm/elGamal/decryption.js

Crypto libraries for front and backend

import { BigInteger as BigInt } from 'jsbn';
import * as Errors from './errors';
import { parseBigInt } from './utils';
import EncryptionElGamal from './encryption';
import * as Utils from "./utils";
export default class DecryptionElGamal extends EncryptionElGamal {
    constructor(p, g, y, x) {
        super(p, g, y);
        this.x = parseBigInt(x);
    }
    decrypt(m) {
        if (!this.x)
            throw new Errors.MissingPrivateKeyError();
        const p = this.p;
        const r = Utils.getRandomBigInt(Utils.BIG_TWO, this.p.subtract(BigInt.ONE));
        const aBlind = this.g.modPow(r, p).multiply(m.a).remainder(p);
        const ax = aBlind.modPow(this.x, p);
        const plaintextBlind = ax.modInverse(p).multiply(m.b).remainder(p);
        return this.y.modPow(r, p).multiply(plaintextBlind).remainder(p);
    }
}