Handle edge case that invalid private key is derived

lib/hdprivatekey.js

@@ -225,6 +225,11 @@ HDPrivateKey.prototype._deriveWithNumber = function(index, hardened, nonComplian
     size: 32
   });
 
+  if (!PrivateKey.isValid(privateKey)) {
+    // Index at this point is already hardened, we can pass null as the hardened arg
+    return this._deriveWithNumber(index + 1, null, nonCompliant);
+  }
+
   var derived = new HDPrivateKey({
     network: this.network,
     depth: this.depth + 1,

test/hdkeys.js

@@ -13,6 +13,7 @@
 var _ = require('lodash');
 var should = require('chai').should();
 var expect = require('chai').expect;
+var sinon = require('sinon');
 var bitcore = require('..');
 var Networks = bitcore.Networks;
 var HDPrivateKey = bitcore.HDPrivateKey;
@@ -253,6 +254,42 @@ describe('BIP32 compliance', function() {
     derived.privateKey.toString().should.equal('4811a079bab267bfdca855b3bddff20231ff7044e648514fa099158472df2836');
   });
 
+  describe('edge cases', function() {
+    var sandbox = sinon.sandbox.create();
+    afterEach(function() {
+      sandbox.restore();
+    });
+    it('will handle edge case that derived private key is invalid', function() {
+      var invalid = new Buffer('0000000000000000000000000000000000000000000000000000000000000000', 'hex');
+      var privateKeyBuffer = new Buffer('5f72914c48581fc7ddeb944a9616389200a9560177d24f458258e5b04527bcd1', 'hex');
+      var chainCodeBuffer = new Buffer('39816057bba9d952fe87fe998b7fd4d690a1bb58c2ff69141469e4d1dffb4b91', 'hex');
+      var unstubbed = bitcore.crypto.BN.prototype.toBuffer;
+      var count = 0;
+      var stub = sandbox.stub(bitcore.crypto.BN.prototype, 'toBuffer', function(args) {
+        // On the fourth call to the function give back an invalid private key
+        // otherwise use the normal behavior.
+        count++;
+        if (count === 4) {
+          return invalid;
+        }
+        var ret = unstubbed.apply(this, arguments);
+        return ret;
+      });
+      sandbox.spy(bitcore.PrivateKey, 'isValid');
+      var key = HDPrivateKey.fromObject({
+        network: 'testnet',
+        depth: 0,
+        parentFingerPrint: 0,
+        childIndex: 0,
+        privateKey: privateKeyBuffer,
+        chainCode: chainCodeBuffer
+      });
+      var derived = key.derive("m/44'");
+      derived.privateKey.toString().should.equal('b15bce3608d607ee3a49069197732c656bca942ee59f3e29b4d56914c1de6825');
+      bitcore.PrivateKey.isValid.callCount.should.equal(2);
+    });
+  });
+
   describe('seed', function() {
 
     it('should initialize a new BIP32 correctly from test vector 1 seed', function() {