wip: implement BigNumber wrapper

lib/BigNumber.js

@@ -0,0 +1,20 @@
+'use strict';
+
+const { jsbn: { BigInteger } } = require('node-forge');
+
+class BigNumber {
+	constructor(value = '') {
+		this._n = new BigInteger(value);
+	}
+
+	toBEBuffer(length = undefined) {
+		const arr = this._n.toByteArray();
+		if (length && arr.length > length)
+			throw new Error('Number out of range.');
+		while (arr.length < length)
+			arr.unshift(0);
+		return Buffer.from(arr);
+	}
+}
+
+module.exports = BigNumber;