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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.// This module is browser compatible.
import { assert } from "../assert/assert.ts";
/** * When checking the values of cryptographic hashes are equal, default * comparisons can be susceptible to timing based attacks, where attacker is * able to find out information about the host system by repeatedly checking * response times to equality comparisons of values. * * It is likely some form of timing safe equality will make its way to the * WebCrypto standard (see: * {@link https://github.com/w3c/webcrypto/issues/270 | w3c/webcrypto#270}), but until * that time, `timingSafeEqual()` is provided: * * ```ts * import { timingSafeEqual } from "https://deno.land/std@$STD_VERSION/crypto/timing_safe_equal.ts"; * import { assert } from "https://deno.land/std@$STD_VERSION/assert/assert.ts"; * * const a = await crypto.subtle.digest( *   "SHA-384", *   new TextEncoder().encode("hello world"), * ); * const b = await crypto.subtle.digest( *   "SHA-384", *   new TextEncoder().encode("hello world"), * ); * * assert(timingSafeEqual(a, b)); * ``` */export function timingSafeEqual(  a: ArrayBufferView | ArrayBufferLike | DataView,  b: ArrayBufferView | ArrayBufferLike | DataView,): boolean {  if (a.byteLength !== b.byteLength) {    return false;  }  if (!(a instanceof DataView)) {    a = ArrayBuffer.isView(a)      ? new DataView(a.buffer, a.byteOffset, a.byteLength)      : new DataView(a);  }  if (!(b instanceof DataView)) {    b = ArrayBuffer.isView(b)      ? new DataView(b.buffer, b.byteOffset, b.byteLength)      : new DataView(b);  }  assert(a instanceof DataView);  assert(b instanceof DataView);  const length = a.byteLength;  let out = 0;  let i = -1;  while (++i < length) {    out |= a.getUint8(i) ^ b.getUint8(i);  }  return out === 0;}