From a8e7f04551d722cc9cdc85e5b6c4fecf660beded Mon Sep 17 00:00:00 2001
From: Alex Mizrahi <alex.mizrahi@gmail.com>
Date: Mon, 30 Oct 2017 21:48:32 +0200
Subject: [PATCH] decoding negative integers, integer decoding tests

---
 lib/asn1/decoders/der.js |  4 ++++
 test/der-decode-test.js  | 17 +++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/lib/asn1/decoders/der.js b/lib/asn1/decoders/der.js
index b2984aa..c8ccecf 100644
--- a/lib/asn1/decoders/der.js
+++ b/lib/asn1/decoders/der.js
@@ -254,6 +254,10 @@ DERNode.prototype._decodeInt = function decodeInt(buffer, values) {
   const raw = buffer.raw();
   let res = new bignum(raw);
 
+  if ((raw[0] & 0x80) > 0) { // negative
+    res = res.fromTwos(raw.length * 8);
+  }
+
   if (values)
     res = values[res.toString(10)] || res;
 
diff --git a/test/der-decode-test.js b/test/der-decode-test.js
index 9d28754..d002dd7 100644
--- a/test/der-decode-test.js
+++ b/test/der-decode-test.js
@@ -3,6 +3,7 @@
 
 const assert = require('assert');
 const asn1 = require('..');
+const bignum = asn1.bignum;
 
 const Buffer = require('buffer').Buffer;
 
@@ -54,6 +55,22 @@ describe('asn1.js DER decoder', function() {
     });
   }
 
+  it('should decode integers', function() {
+    const Int = asn1.define('Int', function () { this.int(); });
+    const values = [
+      ['020101', 1],
+      ['0203008011', 0x8011],
+      ['02020080', 128],
+      ['0201FF', -1],
+      ['020180', -128],
+      ['0202FF7F', -129]
+    ];
+    values.forEach( function (v) {
+      const decoded = Int.decode(new Buffer(v[0], 'hex'), 'der');
+      assert(decoded.eq(new bignum(v[1])), v[1]);
+    });
+  });
+
   test('should decode choice', function() {
     this.choice({
       apple: this.bool(),