Bitcoin address form validation JavaScript and PHP

Here's a JSFiddle: http://jsfiddle.net/timrpeterson/XsCQq/2/

And here's the full code upon which the JSFiddle is based:

<html>
<head>
<script type="text/javascript" src="http://dl.dropboxusercontent.com/u/28441300/BigInt.js"></script> 
<script type="text/javascript" src="http://dl.dropboxusercontent.com/u/28441300/sha256.js"></script> 
</head>
<body>

<div id="text">
</div>

<script type="text/javascript">
var address = "1Eym7pyJcaambv8FG4ZoU8A4xsiL9us2zz";
if (check(address)) {
    document.getElementById('text').innerHTML += "valid";
} else {
    document.getElementById('text').innerHTML += "invalid";
}


function check(address) {
  var decoded = base58_decode(address);     
  if (decoded.length != 25) return false;

  var cksum = decoded.substr(decoded.length - 4); 
  var rest = decoded.substr(0, decoded.length - 4);  

  var good_cksum = hex2a(sha256_digest(hex2a(sha256_digest(rest)))).substr(0, 4);

  if (cksum != good_cksum) return false;
  return true;
}

function base58_decode(string) {
  var table = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz';
  var table_rev = new Array();

  var i;
  for (i = 0; i < 58; i++) {
    table_rev[table[i]] = int2bigInt(i, 8, 0);
  } 

  var l = string.length;
  var long_value = int2bigInt(0, 1, 0);  

  var num_58 = int2bigInt(58, 8, 0);

  var c;
  for(i = 0; i < l; i++) {
    c = string[l - i - 1];
    long_value = add(long_value, mult(table_rev[c], pow(num_58, i)));
  }

  var hex = bigInt2str(long_value, 16);  

  var str = hex2a(hex);  

  var nPad;
  for (nPad = 0; string[nPad] == table[0]; nPad++);  

  var output = str;
  if (nPad > 0) output = repeat("\0", nPad) + str;

  return output;
}

function hex2a(hex) {
    var str = '';
    for (var i = 0; i < hex.length; i += 2)
        str += String.fromCharCode(parseInt(hex.substr(i, 2), 16));
    return str;
}

function a2hex(str) {
    var aHex = "0123456789abcdef";
    var l = str.length;
    var nBuf;
    var strBuf;
    var strOut = "";
    for (var i = 0; i < l; i++) {
      nBuf = str.charCodeAt(i);
      strBuf = aHex[Math.floor(nBuf/16)];
      strBuf += aHex[nBuf % 16];
      strOut += strBuf;
    }
    return strOut;
}

function pow(big, exp) {
    if (exp == 0) return int2bigInt(1, 1, 0);
    var i;
    var newbig = big;
    for (i = 1; i < exp; i++) {
        newbig = mult(newbig, big);
    }

    return newbig;
}

function repeat(s, n){
    var a = [];
    while(a.length < n){
        a.push(s);
    }
    return a.join('');
}
</script>
</body>
</html>

And here is a PHP example (assuming your have PHP BC-Math):

<?php

function checkAddress($address)
{
    $origbase58 = $address;
    $dec = "0";

    for ($i = 0; $i < strlen($address); $i++)
    {
        $dec = bcadd(bcmul($dec,"58",0),strpos("123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz",substr($address,$i,1)),0);
    }

    $address = "";

    while (bccomp($dec,0) == 1)
    {
        $dv = bcdiv($dec,"16",0);
        $rem = (integer)bcmod($dec,"16");
        $dec = $dv;
        $address = $address.substr("0123456789ABCDEF",$rem,1);
    }

    $address = strrev($address);

    for ($i = 0; $i < strlen($origbase58) && substr($origbase58,$i,1) == "1"; $i++)
    {
        $address = "00".$address;
    }

    if (strlen($address)%2 != 0)
    {
        $address = "0".$address;
    }

    if (strlen($address) != 50)
    {
        return false;
    }

    if (hexdec(substr($address,0,2)) > 0)
    {
        return false;
    }

    return substr(strtoupper(hash("sha256",hash("sha256",pack("H*",substr($address,0,strlen($address)-8)),true))),0,8) == substr($address,strlen($address)-8);
}

?>

Here is a better version of @Tim-Peterson 's answer. It fixes the base58 implementation he was using (which would not validate the address "12EJmB3cMGRNveskzA7g7kxW32gSbo2dHF".

I combined the validation code with all the needed libraries and removed a lot that wasn't needed. It only exposes a single api: "checkAddress". I created a little home-page for it, where you can download the module source or the minified version: http://www.julianhaight.com/javascript.shtml

The corrected base58_decode (from https://github.com/cryptocoinjs/bs58):

// from https://github.com/cryptocoinjs/bs58
// Base58 encoding/decoding
// Originally written by Mike Hearn for BitcoinJ
// Copyright (c) 2011 Google Inc
// Ported to JavaScript by Stefan Thomas
// Merged Buffer refactorings from base58-native by Stephen Pair
// Copyright (c) 2013 BitPay Inc

var ALPHABET = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
var ALPHABET_MAP = {}
for(var i = 0; i < ALPHABET.length; i++) {
  ALPHABET_MAP[ALPHABET.charAt(i)] = i
}
var BASE = 58

function base58_decode(string) {
  if (string.length === 0) return []

  var i, j, bytes = [0]
  for (i = 0; i < string.length; i++) {
    var c = string[i]
    if (!(c in ALPHABET_MAP)) throw new Error('Non-base58 character')

    for (j = 0; j < bytes.length; j++) bytes[j] *= BASE
    bytes[0] += ALPHABET_MAP[c]

    var carry = 0
    for (j = 0; j < bytes.length; ++j) {
      bytes[j] += carry

      carry = bytes[j] >> 8
      bytes[j] &= 0xff
    }

    while (carry) {
      bytes.push(carry & 0xff)

      carry >>= 8
    }
  }

  // deal with leading zeros
  for (i = 0; string[i] === '1' && i < string.length - 1; i++) bytes.push(0)

  bytes = bytes.reverse()
  output = '';
  for (i=0; i<bytes.length; i++) {
      output += String.fromCharCode(bytes[i]);
  }
  return output;
}

Tags:

Javascript

Php

Validation

Bitcoin

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