/**
* Experimental KDF for AES.
* @module
*/
import { hkdf } from "./hkdf.js";
import { pbkdf2 as _pbkdf2 } from "./pbkdf2.js";
import { scrypt as _scrypt } from "./scrypt.js";
import { sha256 } from "./sha2.js";
import { abytes, bytesToHex, clean, createView, hexToBytes, kdfInputToBytes, } from "./utils.js";
// A tiny KDF for various applications like AES key-gen.
// Uses HKDF in a non-standard way, so it's not "KDF-secure", only "PRF-secure".
// Which is good enough: assume sha2-256 retained preimage resistance.
// Fixed ESKDF scrypt work factor: interactive-latency target with about 512 MiB RAM per derivation.
const SCRYPT_FACTOR = /* @__PURE__ */ (() => 2 ** 19)();
// Fixed ESKDF PBKDF2 work factor: CPU-only companion branch in the same rough
// interactive-latency range.
const PBKDF2_FACTOR = /* @__PURE__ */ (() => 2 ** 17)();
/**
* Scrypt KDF with the fixed ESKDF policy tuple `{ N: 2^19, r: 8, p: 1, dkLen: 32 }`.
* @param password - user password string, UTF-8 encoded before entering RFC 7914
* @param salt - unique salt string, UTF-8 encoded before entering RFC 7914
* @returns Derived 32-byte key.
* @example
* Derive the 32-byte scrypt key used by ESKDF.
* ```ts
* scrypt('password123', 'user@example.com');
* ```
*/
export function scrypt(password, salt) {
return _scrypt(password, salt, { N: SCRYPT_FACTOR, r: 8, p: 1, dkLen: 32 });
}
/**
* PBKDF2-HMAC-SHA256 with the fixed ESKDF policy tuple `{ sha256, c: 2^17, dkLen: 32 }`.
* @param password - user password string, UTF-8 encoded before entering PBKDF2-HMAC-SHA-256
* @param salt - unique salt string, UTF-8 encoded before entering PBKDF2-HMAC-SHA-256
* @returns Derived 32-byte key.
* @example
* Derive the 32-byte PBKDF2 key used by ESKDF.
* ```ts
* pbkdf2('password123', 'user@example.com');
* ```
*/
export function pbkdf2(password, salt) {
return _pbkdf2(sha256, password, salt, { c: PBKDF2_FACTOR, dkLen: 32 });
}
// Combines two 32-byte byte arrays into a fresh 32-byte result without aliasing either input.
function xor32(a, b) {
abytes(a, 32);
abytes(b, 32);
const arr = new Uint8Array(32);
for (let i = 0; i < 32; i++) {
arr[i] = a[i] ^ b[i];
}
return arr;
}
// All local string length checks are in JS UTF-16 code units, not UTF-8 bytes.
function strHasLength(str, min, max) {
return typeof str === 'string' && str.length >= min && str.length <= max;
}
/**
* Derives main seed. Takes a lot of time; prefer the higher-level `eskdf(...)`
* flow unless you specifically need the raw main seed.
* Derives the main seed by xor'ing two branches:
* the scrypt branch uses a `0x01` separator byte on username/password,
* and the PBKDF2 branch uses `0x02`.
* Username and password strings are encoded by the underlying KDFs after the
* local separator bytes are appended.
* @param username - account identifier used as public salt
* @param password - user password string
* @returns Main 32-byte seed for the account.
* @throws If the username or password length is invalid. {@link Error}
* @example
* Derive the main ESKDF seed from username and password.
* ```ts
* deriveMainSeed('example-user', 'example-password');
* ```
*/
export function deriveMainSeed(username, password) {
if (!strHasLength(username, 8, 255))
throw new Error('invalid username');
if (!strHasLength(password, 8, 255))
throw new Error('invalid password');
// Keep the protocol separators as the literal bytes 0x01 / 0x02 even after minification.
// Embedding them as non-printable characters directly can be awkward across
// JS tooling and environments.
const codes = { _1: 1, _2: 2 };
const sep = { s: String.fromCharCode(codes._1), p: String.fromCharCode(codes._2) };
const scr = scrypt(password + sep.s, username + sep.s);
const pbk = pbkdf2(password + sep.p, username + sep.p);
const res = xor32(scr, pbk);
clean(scr, pbk);
return res;
}
/**
* Converts protocol & accountId pair to HKDF params:
* `info` is UTF-8 protocol bytes, numeric ids become 4-byte BE `salt`,
* and string ids become UTF-8 `salt` bytes.
*/
function getSaltInfo(protocol, accountId = 0) {
// Note that length here also repeats two lines below
// We do an additional length check here to reduce the scope of DoS attacks
if (!(strHasLength(protocol, 3, 15) && /^[a-z0-9]{3,15}$/.test(protocol))) {
throw new Error('invalid protocol');
}
// Exact-match only: substring matches like `assh` / `mentor` must not widen the public whitelist.
const allowsStr = /^(password\d{0,3}|ssh|tor|file)$/.test(protocol);
let salt; // Assigned below: either 4-byte BE account bytes or UTF-8 account bytes.
if (typeof accountId === 'string') {
if (!allowsStr)
throw new Error('accountId must be a number');
if (!strHasLength(accountId, 1, 255))
throw new Error('accountId must be string of length 1..255');
salt = kdfInputToBytes(accountId);
}
else if (Number.isSafeInteger(accountId)) {
if (accountId < 0 || accountId > Math.pow(2, 32) - 1)
throw new Error('invalid accountId');
// Convert to Big Endian Uint32
salt = new Uint8Array(4);
createView(salt).setUint32(0, accountId, false);
}
else {
throw new Error('accountId must be a number' + (allowsStr ? ' or string' : ''));
}
const info = kdfInputToBytes(protocol);
return { salt, info };
}
// Local modulus-size helper, not a general bigint-byte-length primitive:
// `<= 128n` is rejected by ESKDF policy.
function countBytes(num) {
if (typeof num !== 'bigint' || num <= BigInt(128))
throw new Error('invalid number');
return Math.ceil(num.toString(2).length / 8);
}
/**
* Parses keyLength and modulus options to extract length of result key.
* If modulus is used, adds 64 bits to it per the FIPS 186-5 Appendix A.3.1 /
* A.4.1 extra-bits guidance.
*/
function getKeyLength(options) {
if (!options || typeof options !== 'object')
return 32;
const hasLen = 'keyLength' in options;
const hasMod = 'modulus' in options;
if (hasLen && hasMod)
throw new Error('cannot combine keyLength and modulus options');
if (!hasLen && !hasMod)
throw new Error('must have either keyLength or modulus option');
// FIPS 186-5 Appendix A.3.1 / A.4.1 calls for at least 64 extra bits.
const l = hasMod ? countBytes(options.modulus) + 8 : options.keyLength;
if (!(typeof l === 'number' && l >= 16 && l <= 8192))
throw new Error('invalid keyLength');
return l;
}
/**
* Converts key to bigint and divides it by modulus. Big Endian.
* Adapts FIPS 186-5 Appendix A.4.1: `getKeyLength()` already requested the
* extra 64-bit margin, and this step maps the result into `1..modulus-1`.
*/
function modReduceKey(key, modulus) {
const _1 = BigInt(1);
const num = BigInt('0x' + bytesToHex(key)); // check for ui8a, then bytesToNumber()
const res = (num % (modulus - _1)) + _1; // Remove 0 from output
if (res < _1)
throw new Error('expected positive number'); // Guard against bad values
// Strip the extra 64-bit margin that `getKeyLength()` requested
// for bias reduction.
const len = key.length - 8;
const hex = res.toString(16).padStart(len * 2, '0'); // numberToHex()
const bytes = hexToBytes(hex);
if (bytes.length !== len)
throw new Error('invalid length of result key');
return bytes;
}
/**
* ESKDF
* @param username - username, email, or identifier, min: 8 characters, should have enough entropy
* @param password - password, min: 8 characters, should have enough entropy
* @returns Frozen API that derives child keys and exposes the account fingerprint.
* @throws If the username or password length is invalid. {@link Error}
* @example
* Derive account-specific child keys from the main ESKDF seed.
* ```ts
* const kdf = await eskdf('example-university', 'beginning-new-example');
* const key = kdf.deriveChildKey('aes', 0);
* const fingerprint = kdf.fingerprint;
* kdf.expire();
* ```
*/
export async function eskdf(username, password) {
// We are using closure + object instead of class because
// we want to make `seed` non-accessible for any external function.
let seed = deriveMainSeed(username, password);
function deriveCK(protocol, accountId = 0, options) {
// Reject expired instances before deriving any HKDF inputs from the closure-held seed.
abytes(seed, 32);
const { salt, info } = getSaltInfo(protocol, accountId); // validate protocol & accountId
// Validate option shape and coarse length bounds;
// `hkdf()` still rejects non-integer lengths.
const keyLength = getKeyLength(options);
const key = hkdf(sha256, seed, salt, info, keyLength);
// Modulus has already been validated
return options && 'modulus' in options ? modReduceKey(key, options.modulus) : key;
}
function expire() {
// Overwrite the closure-held seed before dropping the reference.
if (seed)
seed.fill(1);
seed = undefined;
}
// prettier-ignore
const fingerprint = Array.from(deriveCK('fingerprint', 0))
.slice(0, 6)
.map((char) => char.toString(16).padStart(2, '0').toUpperCase())
.join(':');
return Object.freeze({ deriveChildKey: deriveCK, expire, fingerprint });
}
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