Analysis on the MD5 method of WeChat applet

/* 
 * A JavaScript implementation of the RSA Data Security, Inc. MD5 Message 
 * Digest Algorithm, as defined in RFC 1321. 
 * Version 1.1 Copyright (C) Paul Johnston 1999 - 2002. 
 * Code also contributed by Greg Holt 
 * See http://pajhome.org.uk/site/legal.html for details. 
 */  
  
/* 
 * Add integers, wrapping at 2^32. This uses 16-bit operations internally 
 * to work around bugs in some JS interpreters. 
 */  
function safe_add(x, y)  
{  
 var lsw = (x & 0xFFFF) + (y & 0xFFFF)  
 var msw = (x >> 16) + (y >> 16) + (lsw >> 16)  
 return (msw << 16) | (lsw & 0xFFFF)  
}  
  
/* 
 * Bitwise rotate a 32-bit number to the left. 
 */  
function rol(num, cnt)  
{  
 return (num << cnt) | (num >>> (32 - cnt))  
}  
  
/* 
 * These functions implement the four basic operations the algorithm uses. 
 */  
function cmn(q, a, b, x, s, t)  
{  
 return safe_add(rol(safe_add(safe_add(a, q), safe_add(x, t)), s), b)  
}  
function ff(a, b, c, d, x, s, t)  
{  
 return cmn((b & c) | ((~b) & d), a, b, x, s, t)  
}  
function gg(a, b, c, d, x, s, t)  
{  
 return cmn((b & d) | (c & (~d)), a, b, x, s, t)  
}  
function hh(a, b, c, d, x, s, t)  
{  
 return cmn(b ^ c ^ d, a, b, x, s, t)  
}  
function ii(a, b, c, d, x, s, t)  
{  
 return cmn(c ^ (b | (~d)), a, b, x, s, t)  
}  
  
/* 
 * Calculate the MD5 of an array of little-endian words, producing an array 
 * of little-endian words. 
 */  
function coreMD5(x)  
{  
 var a = 1732584193  
 var b = -271733879  
 var c = -1732584194  
 var d = 271733878  
  
 for(var i = 0; i < x.length; i += 16)  
 {  
  var olda = a  
  var oldb = b  
  var oldc = c  
  var oldd = d  
  
  a = ff(a, b, c, d, x[i+ 0], 7 , -680876936)  
  d = ff(d, a, b, c, x[i+ 1], 12, -389564586)  
  c = ff(c, d, a, b, x[i+ 2], 17, 606105819)  
  b = ff(b, c, d, a, x[i+ 3], 22, -1044525330)  
  a = ff(a, b, c, d, x[i+ 4], 7 , -176418897)  
  d = ff(d, a, b, c, x[i+ 5], 12, 1200080426)  
  c = ff(c, d, a, b, x[i+ 6], 17, -1473231341)  
  b = ff(b, c, d, a, x[i+ 7], 22, -45705983)  
  a = ff(a, b, c, d, x[i+ 8], 7 , 1770035416)  
  d = ff(d, a, b, c, x[i+ 9], 12, -1958414417)  
  c = ff(c, d, a, b, x[i+10], 17, -42063)  
  b = ff(b, c, d, a, x[i+11], 22, -1990404162)  
  a = ff(a, b, c, d, x[i+12], 7 , 1804603682)  
  d = ff(d, a, b, c, x[i+13], 12, -40341101)  
  c = ff(c, d, a, b, x[i+14], 17, -1502002290)  
  b = ff(b, c, d, a, x[i+15], 22, 1236535329)  
  
  a = gg(a, b, c, d, x[i+ 1], 5 , -165796510)  
  d = gg(d, a, b, c, x[i+ 6], 9 , -1069501632)  
  c = gg(c, d, a, b, x[i+11], 14, 643717713)  
  b = gg(b, c, d, a, x[i+ 0], 20, -373897302)  
  a = gg(a, b, c, d, x[i+ 5], 5 , -701558691)  
  d = gg(d, a, b, c, x[i+10], 9 , 38016083)  
  c = gg(c, d, a, b, x[i+15], 14, -660478335)  
  b = gg(b, c, d, a, x[i+ 4], 20, -405537848)  
  a = gg(a, b, c, d, x[i+ 9], 5 , 568446438)  
  d = gg(d, a, b, c, x[i+14], 9 , -1019803690)  
  c = gg(c, d, a, b, x[i+ 3], 14, -187363961)  
  b = gg(b, c, d, a, x[i+ 8], 20, 1163531501)  
  a = gg(a, b, c, d, x[i+13], 5 , -1444681467)  
  d = gg(d, a, b, c, x[i+ 2], 9 , -51403784)  
  c = gg(c, d, a, b, x[i+ 7], 14, 1735328473)  
  b = gg(b, c, d, a, x[i+12], 20, -1926607734)  
  
  a = hh(a, b, c, d, x[i+ 5], 4 , -378558)  
  d = hh(d, a, b, c, x[i+ 8], 11, -2022574463)  
  c = hh(c, d, a, b, x[i+11], 16, 1839030562)  
  b = hh(b, c, d, a, x[i+14], 23, -35309556)  
  a = hh(a, b, c, d, x[i+ 1], 4 , -1530992060)  
  d = hh(d, a, b, c, x[i+ 4], 11, 1272893353)  
  c = hh(c, d, a, b, x[i+ 7], 16, -155497632)  
  b = hh(b, c, d, a, x[i+10], 23, -1094730640)  
  a = hh(a, b, c, d, x[i+13], 4 , 681279174)  
  d = hh(d, a, b, c, x[i+ 0], 11, -358537222)  
  c = hh(c, d, a, b, x[i+ 3], 16, -722521979)  
  b = hh(b, c, d, a, x[i+ 6], 23, 76029189)  
  a = hh(a, b, c, d, x[i+ 9], 4 , -640364487)  
  d = hh(d, a, b, c, x[i+12], 11, -421815835)  
  c = hh(c, d, a, b, x[i+15], 16, 530742520)  
  b = hh(b, c, d, a, x[i+ 2], 23, -995338651)  
  
  a = ii(a, b, c, d, x[i+ 0], 6 , -198630844)  
  d = ii(d, a, b, c, x[i+ 7], 10, 1126891415)  
  c = ii(c, d, a, b, x[i+14], 15, -1416354905)  
  b = ii(b, c, d, a, x[i+ 5], 21, -57434055)  
  a = ii(a, b, c, d, x[i+12], 6 , 1700485571)  
  d = ii(d, a, b, c, x[i+ 3], 10, -1894986606)  
  c = ii(c, d, a, b, x[i+10], 15, -1051523)  
  b = ii(b, c, d, a, x[i+ 1], 21, -2054922799)  
  a = ii(a, b, c, d, x[i+ 8], 6 , 1873313359)  
  d = ii(d, a, b, c, x[i+15], 10, -30611744)  
  c = ii(c, d, a, b, x[i+ 6], 15, -1560198380)  
  b = ii(b, c, d, a, x[i+13], 21, 1309151649)  
  a = ii(a, b, c, d, x[i+ 4], 6 , -145523070)  
  d = ii(d, a, b, c, x[i+11], 10, -1120210379)  
  c = ii(c, d, a, b, x[i+ 2], 15, 718787259)  
  b = ii(b, c, d, a, x[i+ 9], 21, -343485551)  
  
  a = safe_add(a, olda)  
  b = safe_add(b, oldb)  
  c = safe_add(c, oldc)  
  d = safe_add(d, oldd)  
 }  
 return [a, b, c, d]  
}  
  
/* 
 * Convert an array of little-endian words to a hex string. 
 */  
function binl2hex(binarray)  
{  
 var hex_tab = "0123456789abcdef"  
 var str = ""  
 for(var i = 0; i < binarray.length * 4; i++)  
 {  
  str += hex_tab.charAt((binarray[i>>2] >> ((i%4)*8+4)) & 0xF) +  
      hex_tab.charAt((binarray[i>>2] >> ((i%4)*8)) & 0xF)  
 }  
 return str  
}  
  
/* 
 * Convert an array of little-endian words to a base64 encoded string. 
 */  
function binl2b64(binarray)  
{  
 var tab = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"  
 var str = ""  
 for(var i = 0; i < binarray.length * 32; i += 6)  
 {  
  str += tab.charAt(((binarray[i>>5] << (i%32)) & 0x3F) |  
           ((binarray[i>>5+1] >> (32-i%32)) & 0x3F))  
 }  
 return str  
}  
  
/* 
 * Convert an 8-bit character string to a sequence of 16-word blocks, stored 
 * as an array, and append appropriate padding for MD4/5 calculation. 
 * If any of the characters are >255, the high byte is silently ignored. 
 */  
function str2binl(str)  
{  
 var nblk = ((str.length + 8) >> 6) + 1 // number of 16-word blocks  
 var blks = new Array(nblk * 16)  
 for(var i = 0; i < nblk * 16; i++) blks[i] = 0  
 for(var i = 0; i < str.length; i++)  
  blks[i>>2] |= (str.charCodeAt(i) & 0xFF) << ((i%4) * 8)  
 blks[i>>2] |= 0x80 << ((i%4) * 8)  
 blks[nblk*16-2] = str.length * 8  
 return blks  
}  
  
/* 
 * Convert a wide-character string to a sequence of 16-word blocks, stored as 
 * an array, and append appropriate padding for MD4/5 calculation. 
 */  
function strw2binl(str)  
{  
 var nblk = ((str.length + 4) >> 5) + 1 // number of 16-word blocks  
 var blks = new Array(nblk * 16)  
 for(var i = 0; i < nblk * 16; i++) blks[i] = 0  
 for(var i = 0; i < str.length; i++)  
  blks[i>>1] |= str.charCodeAt(i) << ((i%2) * 16)  
 blks[i>>1] |= 0x80 << ((i%2) * 16)  
 blks[nblk*16-2] = str.length * 16  
 return blks  
}  
  
/* 
 * External interface 
 */  
function hexMD5 (str) { return binl2hex(coreMD5( str2binl(str))) }  
function hexMD5w(str) { return binl2hex(coreMD5(strw2binl(str))) }  
function b64MD5 (str) { return binl2b64(coreMD5( str2binl(str))) }  
function b64MD5w(str) { return binl2b64(coreMD5(strw2binl(str))) }  
/* Backward compatibility */  
function calcMD5(str) { return binl2hex(coreMD5( str2binl(str))) }  
module.exports = {  
 hexMD5: hexMD5  
}

var utilMd5 = require('../../utils/md5.js');  
var password = utilMd5.hexMD5(password);