Mnemonic._entropyChecksum sometimes returning wrong result in IE and Edge

[Flavien]

The result of toString on a number can be different across browsers for large numbers. In particular, it's possible for IE to use exponential notation, which breaks Mnemonic._entropyChecksum.

This can be reproduced using this seed: patrol wise idea oyster inquiry crash dignity chronic scatter time admit pet, which is valid on Chrome and Firefox, but invalid on IE11 and Edge.

I tried a quick fix (https://github.com/bitpay/bitcore-mnemonic/pull/29), but I'm not super familiar with BIP39, and calculating the checksum seems more complicated than what I initially thought.

[Flavien]

Actually, it's worse than that, on IE, the mnemonics generated by Bitcore have an invalid checksum. IE will find them valid, but other browsers won't (and vice versa).

[matiu]

Thanks a lot for the report. We will check it ASAP.

On Sat, Aug 22, 2015 at 7:17 AM, Flavien Charlon notifications@github.com wrote:

Actually, it's worse than that, on IE, the mnemonics generated by Bitcore have an invalid checksum. IE will find them valid, but other browsers won't (and vice versa).

— Reply to this email directly or view it on GitHub https://github.com/bitpay/bitcore-mnemonic/issues/30#issuecomment-133675128 .

BitPay.com

[braydonf]

There are tests against these vectors: https://github.com/trezor/python-mnemonic/blob/master/vectors.json

A possible patch:

diff --git a/lib/mnemonic.js b/lib/mnemonic.js                                                                                                                                                                         
index 70e3e7a..1c25faa 100644                                                                                                                                                                                          
--- a/lib/mnemonic.js                                                                                                                                                                                                  
+++ b/lib/mnemonic.js                                                                                                                                                                                                  
@@ -1,6 +1,7 @@
 'use strict';                                                                                                                                                                                                         

 var bitcore = require('bitcore');                                                                                                                                                                                     
+var BN = bitcore.crypto.BN;                                                                                                                                                                                           
 var unorm = require('unorm');                                                                                                                                                                                         
 var _ = bitcore.deps._;                                                                                                                                                                                               

@@ -274,11 +275,14 @@ Mnemonic._entropyChecksum = function(entropy) {
   var bits = entropy.length * 8;                                                                                                                                                                                      
   var cs = bits / 32;                                                                                                                                                                                                 

-  var hashbits = parseInt(hash.toString('hex'), 16).toString(2);                                                                                                                                                      
+  var hashbitsbn = new BN(hash.toString('hex'), 16);                                                                                                                                                                  
+  var hashbits = hashbitsbn.toString(2);                                                                                                                                                                              
+                                                                                                                                                                                                                      
   // zero pad the hash bits                                                                                                                                                                                           
-  hashbits = (new Array(256).join('0') + hashbits).slice(-256).slice(0, cs);                                                                                                                                          
+  var zerohashbits = (new Array(256).join('0') + hashbits).slice(-256);                                                                                                                                               
+  var checksum = zerohashbits.slice(0, cs);                                                                                                                                                                           

-  return hashbits;                                                                                                                                                                                                    
+  return checksum;                                                                                                                                                                                                    
 };                                                                                                                                                                                                                    

 module.exports = Mnemonic;

However, it could be useful to have a test that is breaking to reveal the problem.

[matiu]

fixed by https://github.com/bitpay/bitcore-mnemonic/pull/33

thanks for the report

[Flavien]

Awesome, thanks. Are you going to update the bower package?

[braydonf]

Should be in the v0.13.2 tag and release.

[braydonf]

Also if you can verify that this fixes the issue, that would be helpful.

[Flavien]

I've just checked, and it works now on Internet Explorer 11 and Edge. Thanks guys.