getRandomValues gives 16- and 32-bit arrays only 8 random bits per element

[inancgumus]

Brief summary

crypto.getRandomValues() never puts a value above 255 into a 16-bit or 32-bit array. A Uint32Array element should carry 32 random bits and carries 8, so anyone using one for a nonce, salt, or token gets far less randomness than they asked for. Uint8Array and Int8Array are fine.

Environment

k6 version: reproduced on v2.2.0. The same code is in v1.8.1, and it has not changed since WebCrypto landed in v0.44.0.

OS: macOS 15 (arm64), not platform specific.

Steps to reproduce the problem

export default function () {
  let max = 0;
  for (let i = 0; i < 1000; i++) {
    const a = new Uint32Array(8);
    crypto.getRandomValues(a);
    max = Math.max(max, ...a);
  }
  console.log("largest of 8000 Uint32Array values:", max);
}

Expected behaviour

A number in the billions, the way browsers and Node do it. The same loop under Node:

node largest: 4294305038

Actual behaviour

largest of 8000 Uint32Array values: 255

Uint16Array has the same ceiling. examples/webcrypto/getRandomValues.js uses a Uint32Array, so the shipped example shows the wrong behaviour too.