PBKDF2 implementation in JS

pbkdf2.js

// A JS implementation of PBKDF2.
// For study only, don't use this.
// Use NodeJS native implementation `crypto.pbkdf2` instead.
const Crypto = require('node:crypto');

function hmac(hmacAlgo, key, data) {
    return Crypto.createHmac(hmacAlgo, key).update(data).digest();
}

const BUF_INT32_BE = Buffer.alloc(4);

function f(hmacAlgo, password, salt, i, c) {
    BUF_INT32_BE.writeUInt32BE(i, 0);
    const f = hmac(hmacAlgo, password, Buffer.concat([salt, BUF_INT32_BE]));
    let u = f;
    for (let i = 1; i < c; i++) {
        u = hmac(hmacAlgo, password, u);
        for (let j = 0; j < f.length; j++) {
            f[j] ^= u[j];
        }
    }
    return f;
}

/**
 * @param {string} hmacAlgo     The digest algo to be used with HMAC.
 * @param {Buffer} password     The password/passphrase
 * @param {Buffer} salt         The cryptography salt
 * @param {number} iterations   The count of iterations
 * @param {number} keylen       The byte-length of final key output
 *
 * @example pbkdf2('sha256', Buffer.from('password'), Buffer.from('salt'), 100000, 64);
 */
exports.pbkdf2 = function(hmacAlgo, password, salt, iterations, keylen) {

    let dk = Buffer.allocUnsafe(0);

    let i = 1;
    while (dk.length < keylen) {
        const u = f(hmacAlgo, password, salt, i++, iterations);
        dk = Buffer.concat([dk, u]);
    }
    return dk.subarray(0, keylen);
};