miscreant/release/internals/constant-time.js

Misuse resistant symmetric encryption library providing AES-SIV (RFC 5297), AES-PMAC-SIV, and STREAM constructions

"use strict";
// Copyright (C) 2016 Dmitry Chestnykh
// MIT License. See LICENSE file for details.
Object.defineProperty(exports, "__esModule", { value: true });
/**
 * NOTE! Due to the inability to guarantee real constant time evaluation of
 * anything in JavaScript VM, this is module is the best effort.
 */
/**
 * Returns resultIfOne if subject is 1, or resultIfZero if subject is 0.
 *
 * Supports only 32-bit integers, so resultIfOne or resultIfZero are not
 * integers, they'll be converted to them with bitwise operations.
 */
function select(subject, resultIfOne, resultIfZero) {
    return (~(subject - 1) & resultIfOne) | ((subject - 1) & resultIfZero);
}
exports.select = select;
/**
 * Returns 1 if a and b are of equal length and their contents
 * are equal, or 0 otherwise.
 *
 * Note that unlike in equal(), zero-length inputs are considered
 * the same, so this function will return 1.
 */
function compare(a, b) {
    if (a.length !== b.length) {
        return 0;
    }
    let result = 0;
    for (let i = 0; i < a.length; i++) {
        result |= a[i] ^ b[i];
    }
    return (1 & ((result - 1) >>> 8));
}
exports.compare = compare;
/**
 * Returns true if a and b are of equal non-zero length,
 * and their contents are equal, or false otherwise.
 *
 * Note that unlike in compare() zero-length inputs are considered
 * _not_ equal, so this function will return false.
 */
function equal(a, b) {
    if (a.length === 0 || b.length === 0) {
        return false;
    }
    return compare(a, b) !== 0;
}
exports.equal = equal;