Major changes. Separating responsibilities. Orders builder, serializer.

lib/crypto/MGF1.js

@@ -0,0 +1,48 @@
+'use strict';
+
+const crypto = require('crypto');
+const BN = require('bn.js');
+
+const MFG_LEN = 32;
+
+const divceil = (a, b) => ~~(((a + b) - 1) / b); // eslint-disable-line no-bitwise
+const rjust = (string, width, padding) => {
+	padding = padding || ' ';
+	padding = padding.substr(0, 1);
+	if (string.length < width)
+		return padding.repeat(width - string.length) + string;
+	return string;
+};
+const xor = (a, b) => {
+	if (a.length !== b.length)
+		throw new Error('Different length for a and b');
+
+	for (let i = 0; i < a.length; i++)
+		a[i] ^= b[i]; // eslint-disable-line no-bitwise
+
+	return a;
+};
+const i2osp = (x, len) => {
+	if (x >= 256 ** len)
+		throw new Error('Integer too large');
+
+	return Buffer.from(rjust((Buffer.from((new BN(x)).toArray('be', 4)).toString()).replace(/\x00/gi, ''), len, '\x00')); // eslint-disable-line no-control-regex
+};
+
+module.exports = {
+	generate(seed, masklen) {
+		if (masklen > 4294967296 * MFG_LEN)
+			throw new Error('Mask too long');
+
+
+		const b = [];
+
+		for (let i = 0; i < divceil(masklen, MFG_LEN); i++)
+			b[i] = crypto.createHash('sha256').update(Buffer.concat([seed, i2osp(i, 4)])).digest();
+
+
+		return (Buffer.concat(b)).slice(0, masklen);
+	},
+	xor,
+	rjust,
+};