From 5ace2137231af9a3563ab31fa0f70fbdf4b148cb Mon Sep 17 00:00:00 2001
From: Vladislav Hristov <vlad@Vladislavs-Mac-mini.local>
Date: Thu, 31 May 2018 11:33:59 +0300
Subject: [PATCH] Add sign, _emsaPSS and _modPowe methods in Key.js file

---
 lib/Key.js | 47 ++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 44 insertions(+), 3 deletions(-)

diff --git a/lib/Key.js b/lib/Key.js
index bd48a06..7f44565 100644
--- a/lib/Key.js
+++ b/lib/Key.js
@@ -2,8 +2,10 @@
 
 const crypto = require('crypto');
 
-const NodeRSA = require("node-rsa");
 const BN      = require('bn.js');
+const NodeRSA = require("node-rsa");
+
+const MGF1    = require('./MGF1');
 
 module.exports = class Key {
     constructor(encodedKey, passphrase = null) {
@@ -20,8 +22,8 @@ module.exports = class Key {
 		return crypto.createHash('sha256').update(str).digest('base64').trim();
 	};
 
-	publicEncrypt(str) {
-		return this.key.encrypt(str);
+	publicEncrypt(buf) {
+		return crypto.publicEncrypt({ 'key': this.toPem(), padding: crypto.constants.RSA_PKCS1_PADDING }, buf);
 	}
 
     n() {
@@ -35,4 +37,43 @@ module.exports = class Key {
 	toPem() {
 		return this.key.isPrivate() ? this.key.exportKey("pkcs1-private-pem") : this.key.exportKey("pkcs8-public-pem");
 	}
+
+	sign(msg, salt = crypto.randomBytes(32)) {
+		const base  = new BN(this._emsaPSS(msg, salt));
+		const power = new BN(this.key.keyPair.d.toBuffer());
+		const mod   = new BN(this.key.keyPair.n.toBuffer());
+
+		return (this._modPow(base, power, mod)).toBuffer().toString('base64');
+	}
+
+	_emsaPSS(msg, salt) {
+		const eightNullBytes = Buffer.from("\x00".repeat(8));
+		const digestedMsg    = crypto.createHash('sha256').update(msg).digest();
+		const mTickHash      = crypto.createHash('sha256').update(Buffer.concat([eightNullBytes, digestedMsg, salt]), 'binary').digest();
+
+		const ps             = Buffer.from("\x00".repeat(190));
+		const db             = Buffer.concat([ps, Buffer.from("\x01"), salt]);
+
+		const dbMask         = MGF1.generate(mTickHash, db.length);
+		const maskedDb       = MGF1.xor(db, dbMask);					// so far so good
+
+		let maskedDbMsb      = (new MGF1)._rjust(new BN(maskedDb.slice(0, 1), 2).toString(2), 8, "0");
+		maskedDbMsb          = "0" + maskedDbMsb.substr(1);
+
+		maskedDb[0]          = (new BN(maskedDbMsb, 2).toBuffer())[0];
+
+		return Buffer.concat([maskedDb, mTickHash, Buffer.from('BC', 'hex')]);
+	}
+
+	_modPow(base, power, mod) {
+		let result = new BN(1);
+
+		while( power > 0 ) {
+			result = power.and(new BN(1)) == 1 ? (result.mul(base)).mod(mod) : result;
+			base = (base.mul(base)).mod(mod);
+			power = power.shrn(1);
+		}
+
+		return result;
+	}
 };