简述Javascript MD4

/*
 * A JavaScript implementation of the RSA Data Security, Inc. MD4 Message
 * Digest Algorithm, as defined in RFC 1320.
 * Version 2.1 Copyright (C) Jerrad Pierce, Paul Johnston 1999 - 2002.
 * Other contributors: Greg Holt, Andrew Kepert, Ydnar, Lostinet
 * Distributed under the BSD License
 * See http://pajhome.org.uk/crypt/md5 for more info.
 */

/*
 * Configurable variables. You may need to tweak these to be compatible with
 * the server-side, but the defaults work in most cases.
 */
var hexcase = 0; /* hex output format. 0 - lowercase; 1 - uppercase    */
var b64pad = ""; /* base-64 pad character. "=" for strict RFC compliance  */
var chrsz  = 8; /* bits per input character. 8 - ASCII; 16 - Unicode   */

/*
 * These are the functions you'll usually want to call
 */
function hex_md4(s){ return binl2hex(core_md4(str2binl(s), s.length * chrsz));}
function b64_md4(s){ return binl2b64(core_md4(str2binl(s), s.length * chrsz));}
function str_md4(s){ return binl2str(core_md4(str2binl(s), s.length * chrsz));}
function hex_hmac_md4(key, data) { return binl2hex(core_hmac_md4(key, data)); }
function b64_hmac_md4(key, data) { return binl2b64(core_hmac_md4(key, data)); }
function str_hmac_md4(key, data) { return binl2str(core_hmac_md4(key, data)); }

/* 
 * Perform a simple self-test to see if the VM is working 
 */
function md4_vm_test()
{
 return hex_md4("abc") == "a448017aaf21d8525fc10ae87aa6729d";
}

/*
 * Calculate the MD4 of an array of little-endian words, and a bit length
 */
function core_md4(x, len)
{
 /* append padding */
 x[len >> 5] |= 0x80 << (len % 32);
 x[(((len + 64) >>> 9) << 4) + 14] = len;
 
 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 = md4_ff(a, b, c, d, x[i+ 0], 3 );
  d = md4_ff(d, a, b, c, x[i+ 1], 7 );
  c = md4_ff(c, d, a, b, x[i+ 2], 11);
  b = md4_ff(b, c, d, a, x[i+ 3], 19);
  a = md4_ff(a, b, c, d, x[i+ 4], 3 );
  d = md4_ff(d, a, b, c, x[i+ 5], 7 );
  c = md4_ff(c, d, a, b, x[i+ 6], 11);
  b = md4_ff(b, c, d, a, x[i+ 7], 19);
  a = md4_ff(a, b, c, d, x[i+ 8], 3 );
  d = md4_ff(d, a, b, c, x[i+ 9], 7 );
  c = md4_ff(c, d, a, b, x[i+10], 11);
  b = md4_ff(b, c, d, a, x[i+11], 19);
  a = md4_ff(a, b, c, d, x[i+12], 3 );
  d = md4_ff(d, a, b, c, x[i+13], 7 );
  c = md4_ff(c, d, a, b, x[i+14], 11);
  b = md4_ff(b, c, d, a, x[i+15], 19);

  a = md4_gg(a, b, c, d, x[i+ 0], 3 );
  d = md4_gg(d, a, b, c, x[i+ 4], 5 );
  c = md4_gg(c, d, a, b, x[i+ 8], 9 );
  b = md4_gg(b, c, d, a, x[i+12], 13);
  a = md4_gg(a, b, c, d, x[i+ 1], 3 );
  d = md4_gg(d, a, b, c, x[i+ 5], 5 );
  c = md4_gg(c, d, a, b, x[i+ 9], 9 );
  b = md4_gg(b, c, d, a, x[i+13], 13);
  a = md4_gg(a, b, c, d, x[i+ 2], 3 );
  d = md4_gg(d, a, b, c, x[i+ 6], 5 );
  c = md4_gg(c, d, a, b, x[i+10], 9 );
  b = md4_gg(b, c, d, a, x[i+14], 13);
  a = md4_gg(a, b, c, d, x[i+ 3], 3 );
  d = md4_gg(d, a, b, c, x[i+ 7], 5 );
  c = md4_gg(c, d, a, b, x[i+11], 9 );
  b = md4_gg(b, c, d, a, x[i+15], 13);

  a = md4_hh(a, b, c, d, x[i+ 0], 3 );
  d = md4_hh(d, a, b, c, x[i+ 8], 9 );
  c = md4_hh(c, d, a, b, x[i+ 4], 11);
  b = md4_hh(b, c, d, a, x[i+12], 15);
  a = md4_hh(a, b, c, d, x[i+ 2], 3 );
  d = md4_hh(d, a, b, c, x[i+10], 9 );
  c = md4_hh(c, d, a, b, x[i+ 6], 11);
  b = md4_hh(b, c, d, a, x[i+14], 15);
  a = md4_hh(a, b, c, d, x[i+ 1], 3 );
  d = md4_hh(d, a, b, c, x[i+ 9], 9 );
  c = md4_hh(c, d, a, b, x[i+ 5], 11);
  b = md4_hh(b, c, d, a, x[i+13], 15);
  a = md4_hh(a, b, c, d, x[i+ 3], 3 );
  d = md4_hh(d, a, b, c, x[i+11], 9 );
  c = md4_hh(c, d, a, b, x[i+ 7], 11);
  b = md4_hh(b, c, d, a, x[i+15], 15);

  a = safe_add(a, olda);
  b = safe_add(b, oldb);
  c = safe_add(c, oldc);
  d = safe_add(d, oldd);

 }
 return Array(a, b, c, d);

}

/*
 * These functions implement the basic operation for each round of the
 * algorithm.
 */
function md4_cmn(q, a, b, x, s, t)
{
 return safe_add(rol(safe_add(safe_add(a, q), safe_add(x, t)), s), b);
}
function md4_ff(a, b, c, d, x, s)
{
 return md4_cmn((b & c) | ((~b) & d), a, 0, x, s, 0);
}
function md4_gg(a, b, c, d, x, s)
{
 return md4_cmn((b & c) | (b & d) | (c & d), a, 0, x, s, 1518500249);
}
function md4_hh(a, b, c, d, x, s)
{
 return md4_cmn(b ^ c ^ d, a, 0, x, s, 1859775393);
}

/*
 * Calculate the HMAC-MD4, of a key and some data
 */
function core_hmac_md4(key, data)
{
 var bkey = str2binl(key);
 if(bkey.length > 16) bkey = core_md4(bkey, key.length * chrsz);

 var ipad = Array(16), opad = Array(16);
 for(var i = 0; i < 16; i++) 
 {
  ipad[i] = bkey[i] ^ 0x36363636;
  opad[i] = bkey[i] ^ 0x5C5C5C5C;
 }

 var hash = core_md4(ipad.concat(str2binl(data)), 512 + data.length * chrsz);
 return core_md4(opad.concat(hash), 512 + 128);
}

/*
 * 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));
}

/*
 * Convert a string to an array of little-endian words
 * If chrsz is ASCII, characters >255 have their hi-byte silently ignored.
 */
function str2binl(str)
{
 var bin = Array();
 var mask = (1 << chrsz) - 1;
 for(var i = 0; i < str.length * chrsz; i += chrsz)
  bin[i>>5] |= (str.charCodeAt(i / chrsz) & mask) << (i%32);
 return bin;
}

/*
 * Convert an array of little-endian words to a string
 */
function binl2str(bin)
{
 var str = "";
 var mask = (1 << chrsz) - 1;
 for(var i = 0; i < bin.length * 32; i += chrsz)
  str += String.fromCharCode((bin[i>>5] >>> (i % 32)) & mask);
 return str;
}

/*
 * Convert an array of little-endian words to a hex string.
 */
function binl2hex(binarray)
{
 var hex_tab = hexcase ? "0123456789ABCDEF" : "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 base-64 string
 */
function binl2b64(binarray)
{
 var tab = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 var str = "";
 for(var i = 0; i < binarray.length * 4; i += 3)
 {
  var triplet = (((binarray[i  >> 2] >> 8 * ( i  %4)) & 0xFF) << 16)
        | (((binarray[i+1 >> 2] >> 8 * ((i+1)%4)) & 0xFF) << 8 )
        | ((binarray[i+2 >> 2] >> 8 * ((i+2)%4)) & 0xFF);
  for(var j = 0; j < 4; j++)
  {
   if(i * 8 + j * 6 > binarray.length * 32) str += b64pad;
   else str += tab.charAt((triplet >> 6*(3-j)) & 0x3F);
  }
 }
 return str;
}