@kotevode/ffjavascript/src/chacha.js

Finite Field Library in Javascript

import * as Scalar from "./scalar.js";


function quarterRound(st, a, b, c, d) {

    st[a] = (st[a] + st[b]) >>> 0;
    st[d] = (st[d] ^ st[a]) >>> 0;
    st[d] = ((st[d] << 16) | ((st[d]>>>16) & 0xFFFF)) >>> 0;

    st[c] = (st[c] + st[d]) >>> 0;
    st[b] = (st[b] ^ st[c]) >>> 0;
    st[b] = ((st[b] << 12) | ((st[b]>>>20) & 0xFFF)) >>> 0;

    st[a] = (st[a] + st[b]) >>> 0;
    st[d] = (st[d] ^ st[a]) >>> 0;
    st[d] = ((st[d] << 8) | ((st[d]>>>24) & 0xFF)) >>> 0;

    st[c] = (st[c] + st[d]) >>> 0;
    st[b] = (st[b] ^ st[c]) >>> 0;
    st[b] = ((st[b] << 7) | ((st[b]>>>25) & 0x7F)) >>> 0;
}

function doubleRound(st) {
    quarterRound(st, 0, 4, 8,12);
    quarterRound(st, 1, 5, 9,13);
    quarterRound(st, 2, 6,10,14);
    quarterRound(st, 3, 7,11,15);

    quarterRound(st, 0, 5,10,15);
    quarterRound(st, 1, 6,11,12);
    quarterRound(st, 2, 7, 8,13);
    quarterRound(st, 3, 4, 9,14);
}

export default class ChaCha {

    constructor(seed) {
        seed = seed || [0,0,0,0,0,0,0,0];
        this.state = [
            0x61707865,
            0x3320646E,
            0x79622D32,
            0x6B206574,
            seed[0],
            seed[1],
            seed[2],
            seed[3],
            seed[4],
            seed[5],
            seed[6],
            seed[7],
            0,
            0,
            0,
            0
        ];
        this.idx = 16;
        this.buff = new Array(16);
    }

    nextU32() {
        if (this.idx == 16) this.update();
        return this.buff[this.idx++];
    }

    nextU64() {
        return Scalar.add(Scalar.mul(this.nextU32(), 0x100000000), this.nextU32());
    }

    nextBool() {
        return (this.nextU32() & 1) == 1;
    }

    update() {
        // Copy the state
        for (let i=0; i<16; i++) this.buff[i] = this.state[i];

        // Apply the rounds
        for (let i=0; i<10; i++) doubleRound(this.buff);

        // Add to the initial
        for (let i=0; i<16; i++) this.buff[i] = (this.buff[i] + this.state[i]) >>> 0;

        this.idx = 0;

        this.state[12] = (this.state[12] + 1) >>> 0;
        if (this.state[12] != 0) return;
        this.state[13] = (this.state[13] + 1) >>> 0;
        if (this.state[13] != 0) return;
        this.state[14] = (this.state[14] + 1) >>> 0;
        if (this.state[14] != 0) return;
        this.state[15] = (this.state[15] + 1) >>> 0;
    }
}