I am trying to read "old" node-scrypt hashes with scrypt-async. So far with little success. This script needs `scrypt` and `scrypt-async` installed via `npm`

node-scrypt-to-scrypt-async.js

/* ATTEMPT TO PARSE A node-scrypt STRING CORRECTLY FOR USE WITH scrypt-async */

var scrypt = require('scrypt-async');
var scryptOld = require('scrypt');
var crypto = require('crypto');

// Format as seen in node-scrypt, written by Barry Steyn. Scrypt by Colin Percival.
// https://github.com/barrysteyn/node-scrypt/blob/master/scrypt/scrypt-1.2.0/keyderivation.c#L60-L77 and
// https://security.stackexchange.com/a/91050/50616
// scrypt paper: https://www.tarsnap.com/scrypt/scrypt.pdf (not helpful for this :-( )
function parseScrypt(hexString) {
	var b = Buffer.from(hexString, "hex");
	var sha256 = crypto.createHash('SHA256');

	if (b.toString("ASCII", 0, 6) !== 'scrypt') {
		throw "this is not scrypt";
	}

	var parsed = {
		first64bytes: b.slice(0, 64),
		logN: b.readUInt8(7),
		r: b.readUInt32BE(8),
		p: b.readUInt32BE(12),
		salt: b.slice(16, 48),
		checksum: b.slice(48, 64),
		signature: b.slice(64, 96)
	};

	sha256.update(b.slice(0, 48));
	var digest = sha256.digest().slice(0, 16);
	if (Buffer.compare(digest, parsed.checksum) !== 0) {
		throw "something is odd while parsing: checksums do not match";
	}
		
	return parsed;
}


// testing: this generates a hash from node-scrypt.
var hash = scryptOld.kdfSync("hello", scryptOld.paramsSync(0.1)).toString("hex"); 

// we'll parse it using our function from above.
var scryptParams = parseScrypt(hash);
console.log(scryptParams);
console.log("->   original: %s", scryptParams.signature.toString("hex"));

// let's see if we can verify it! This means recreating a hash with the same parameters and trying to get the same result.
scrypt(Buffer.from("hello", "UTF-8"), scryptParams.salt, {
	logN: scryptParams.logN,
	r: scryptParams.r,
	p: scryptParams.p,
	dkLen: 64,  // **** CHANGED ***
	encoding: "binary" // *** CHANGED ***
}, function (key) {
         // ***** ADDED ****
	var hmacKey = key.subarray(32);
	var result = crypto.createHmac('sha256', hmacKey).update(scryptParams.first64bytes).digest("hex");
	console.log("-> comparison: %s", result);
});

this revision includes changes by @dchest suggested in dchest/scrypt-async-js#44 (comment)