bip39pad.js

var bip39 = require('bip39');
if (!String.prototype.repeat) {
    String.prototype.repeat = function(count) {
        'use strict';
        if (this == null) {
            throw new TypeError('can\'t convert ' + this + ' to object');
        }
        var str = '' + this;
        count = +count;
        if (count != count) {
            count = 0;
        }
        if (count < 0) {
            throw new RangeError('repeat count must be non-negative');
        }
        if (count == Infinity) {
            throw new RangeError('repeat count must be less than infinity');
        }
        count = Math.floor(count);
        if (str.length == 0 || count == 0) {
            return '';
        }
        // Ensuring count is a 31-bit integer allows us to heavily optimize the
        // main part. But anyway, most current (August 2014) browsers can't handle
        // strings 1 << 28 chars or longer, so:
        if (str.length * count >= 1 << 28) {
            throw new RangeError('repeat count must not overflow maximum string size');
        }
        var rpt = '';
        for (;;) {
            if ((count & 1) == 1) {
                rpt += str;
            }
            count >>>= 1;
            if (count == 0) {
                break;
            }
            str += str;
        }
        // Could we try:
        // return Array(count + 1).join(this);
        return rpt;
    }
}


// create original mock entropy buffer
var entropyBuffer = new Buffer('11'.repeat(65), 'hex');

// this fails
try {
    console.log('entropyToMnemonic: ' + bip39.entropyToMnemonic(entropyBuffer));
    console.log("length: " + bip39.entropyToMnemonic(entropyBuffer).split(" ").length);
    console.log('mnemonicToEntropy: ' + bip39.mnemonicToEntropy(bip39.entropyToMnemonic(entropyBuffer)));
} catch (e) {
    console.error("" + e);
}

// length of entropy in bytes
var entropyByteLength = entropyBuffer.length;
console.log('entropyByteLength: ' + entropyByteLength);

// payload for mnemonic including checksum
var bip39ByteLength = (entropyByteLength + entropyByteLength / 32.0);
var bip39BitsLength = bip39ByteLength * 8;
console.log('bip39ByteLength: ' + bip39ByteLength);

// words is ceil of chunks of 11 bits
var words = Math.ceil(bip39BitsLength / 11);
console.log('words: ' + words);

// words need to be %3==0 so we fix the word count
words = words + (3 - words % 3);
console.log('words: ' + words);

// reverse of the entropyByteLength -> words formula
var requiredBitsLength = ((words * 32) / 33) * 11;
var requiredByteLength = Math.floor(requiredBitsLength / 8);
console.log('requiredByteLength: ' + requiredByteLength);

// padd the entropy
entropyBuffer = Buffer.concat([new Buffer('00'.repeat(requiredByteLength - entropyByteLength), 'hex'), entropyBuffer]);

console.log('entropyToMnemonic: ' + bip39.entropyToMnemonic(entropyBuffer));
console.log("length: " + bip39.entropyToMnemonic(entropyBuffer).split(" ").length);
console.log('mnemonicToEntropy: ' + bip39.mnemonicToEntropy(bip39.entropyToMnemonic(entropyBuffer)));