javascript - How to decode/decrypt MD5 encryption using Java

Question

I am using the ExtJS framework. I have a MD5 function in JavaScript to encrypt some JSON. My backend uses Java so I wanted to know how to decrypt an MD5 Javascript encryption using Java?

Here is the JS equiv of MD5 function that I am using:

Ext.util.MD5 = function(s,raw,hexcase,chrsz) {
        raw = raw || false;     
        hexcase = hexcase || false;
        chrsz = chrsz || 8;

        function safe_add(x, y){
                var lsw = (x & 0xFFFF) + (y & 0xFFFF);
                var msw = (x >> 16) + (y >> 16) + (lsw >> 16);
                return (msw << 16) | (lsw & 0xFFFF);
        }
        function bit_rol(num, cnt){
                return (num << cnt) | (num >>> (32 - cnt));
        }
        function md5_cmn(q, a, b, x, s, t){
                return safe_add(bit_rol(safe_add(safe_add(a, q), safe_add(x, t)), s),b);
        }
        function md5_ff(a, b, c, d, x, s, t){
                return md5_cmn((b & c) | ((~b) & d), a, b, x, s, t);
        }
        function md5_gg(a, b, c, d, x, s, t){
                return md5_cmn((b & d) | (c & (~d)), a, b, x, s, t);
        }
        function md5_hh(a, b, c, d, x, s, t){
                return md5_cmn(b ^ c ^ d, a, b, x, s, t);
        }
        function md5_ii(a, b, c, d, x, s, t){
                return md5_cmn(c ^ (b | (~d)), a, b, x, s, t);
        }

        function core_md5(x, len){
                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 = md5_ff(a, b, c, d, x[i+ 0], 7 , -680876936);
                        d = md5_ff(d, a, b, c, x[i+ 1], 12, -389564586);
                        c = md5_ff(c, d, a, b, x[i+ 2], 17,  606105819);
                        b = md5_ff(b, c, d, a, x[i+ 3], 22, -1044525330);
                        a = md5_ff(a, b, c, d, x[i+ 4], 7 , -176418897);
                        d = md5_ff(d, a, b, c, x[i+ 5], 12,  1200080426);
                        c = md5_ff(c, d, a, b, x[i+ 6], 17, -1473231341);
                        b = md5_ff(b, c, d, a, x[i+ 7], 22, -45705983);
                        a = md5_ff(a, b, c, d, x[i+ 8], 7 ,  1770035416);
                        d = md5_ff(d, a, b, c, x[i+ 9], 12, -1958414417);
                        c = md5_ff(c, d, a, b, x[i+10], 17, -42063);
                        b = md5_ff(b, c, d, a, x[i+11], 22, -1990404162);
                        a = md5_ff(a, b, c, d, x[i+12], 7 ,  1804603682);
                        d = md5_ff(d, a, b, c, x[i+13], 12, -40341101);
                        c = md5_ff(c, d, a, b, x[i+14], 17, -1502002290);
                        b = md5_ff(b, c, d, a, x[i+15], 22,  1236535329);
                        a = md5_gg(a, b, c, d, x[i+ 1], 5 , -165796510);
                        d = md5_gg(d, a, b, c, x[i+ 6], 9 , -1069501632);
                        c = md5_gg(c, d, a, b, x[i+11], 14,  643717713);
                        b = md5_gg(b, c, d, a, x[i+ 0], 20, -373897302);
                        a = md5_gg(a, b, c, d, x[i+ 5], 5 , -701558691);
                        d = md5_gg(d, a, b, c, x[i+10], 9 ,  38016083);
                        c = md5_gg(c, d, a, b, x[i+15], 14, -660478335);
                        b = md5_gg(b, c, d, a, x[i+ 4], 20, -405537848);
                        a = md5_gg(a, b, c, d, x[i+ 9], 5 ,  568446438);
                        d = md5_gg(d, a, b, c, x[i+14], 9 , -1019803690);
                        c = md5_gg(c, d, a, b, x[i+ 3], 14, -187363961);
                        b = md5_gg(b, c, d, a, x[i+ 8], 20,  1163531501);
                        a = md5_gg(a, b, c, d, x[i+13], 5 , -1444681467);
                        d = md5_gg(d, a, b, c, x[i+ 2], 9 , -51403784);
                        c = md5_gg(c, d, a, b, x[i+ 7], 14,  1735328473);
                        b = md5_gg(b, c, d, a, x[i+12], 20, -1926607734);
                        a = md5_hh(a, b, c, d, x[i+ 5], 4 , -378558);
                        d = md5_hh(d, a, b, c, x[i+ 8], 11, -2022574463);
                        c = md5_hh(c, d, a, b, x[i+11], 16,  1839030562);
                        b = md5_hh(b, c, d, a, x[i+14], 23, -35309556);
                        a = md5_hh(a, b, c, d, x[i+ 1], 4 , -1530992060);
                        d = md5_hh(d, a, b, c, x[i+ 4], 11,  1272893353);
                        c = md5_hh(c, d, a, b, x[i+ 7], 16, -155497632);
                        b = md5_hh(b, c, d, a, x[i+10], 23, -1094730640);
                        a = md5_hh(a, b, c, d, x[i+13], 4 ,  681279174);
                        d = md5_hh(d, a, b, c, x[i+ 0], 11, -358537222);
                        c = md5_hh(c, d, a, b, x[i+ 3], 16, -722521979);
                        b = md5_hh(b, c, d, a, x[i+ 6], 23,  76029189);
                        a = md5_hh(a, b, c, d, x[i+ 9], 4 , -640364487);
                        d = md5_hh(d, a, b, c, x[i+12], 11, -421815835);
                        c = md5_hh(c, d, a, b, x[i+15], 16,  530742520);
                        b = md5_hh(b, c, d, a, x[i+ 2], 23, -995338651);
                        a = md5_ii(a, b, c, d, x[i+ 0], 6 , -198630844);
                        d = md5_ii(d, a, b, c, x[i+ 7], 10,  1126891415);
                        c = md5_ii(c, d, a, b, x[i+14], 15, -1416354905);
                        b = md5_ii(b, c, d, a, x[i+ 5], 21, -57434055);
                        a = md5_ii(a, b, c, d, x[i+12], 6 ,  1700485571);
                        d = md5_ii(d, a, b, c, x[i+ 3], 10, -1894986606);
                        c = md5_ii(c, d, a, b, x[i+10], 15, -1051523);
                        b = md5_ii(b, c, d, a, x[i+ 1], 21, -2054922799);
                        a = md5_ii(a, b, c, d, x[i+ 8], 6 ,  1873313359);
                        d = md5_ii(d, a, b, c, x[i+15], 10, -30611744);
                        c = md5_ii(c, d, a, b, x[i+ 6], 15, -1560198380);
                        b = md5_ii(b, c, d, a, x[i+13], 21,  1309151649);
                        a = md5_ii(a, b, c, d, x[i+ 4], 6 , -145523070);
                        d = md5_ii(d, a, b, c, x[i+11], 10, -1120210379);
                        c = md5_ii(c, d, a, b, x[i+ 2], 15,  718787259);
                        b = md5_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];
        }
        function str2binl(str){
                var bin = [];
                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;
        }
        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;
        }

        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;
        }
        return (raw ? binl2str(core_md5(str2binl(s), s.length * chrsz)) : binl2hex(core_md5(str2binl(s), s.length * chrsz))     );
};

Answer 1

MD5 is a hash (i.e. one-way transformation), so you can't decrypt it. You can compare a known hash with hash computed from a cleartext to verify validity of input. Java has inbuilt library for this. I have used this code below, adapt as necessary, also verify that your hashes generated in javascript have the same encoding.

import java.security.MessageDigest;    
import sun.misc.BASE64Encoder;

public class MD5Sample {
  /**
   * Cipher for encode
   */
  private final MessageDigest md;

  public MD5Sample() throws SecurityException {
    try {
      md = MessageDigest.getInstance("MD5", "SUN");
    }catch(Exception se) {
      throw new SecurityException("In MD5 constructor " + se);
    }
  }

  public String encode(String in) throws Exception {
    if (in == null) {
      return null;
    }
    try {
      byte[] raw = null;
      byte[] stringBytes = null;
      stringBytes = in.getBytes("UTF8");
      synchronized(md) {
        raw = md.digest(stringBytes);
      }
      BASE64Encoder encoder = new BASE64Encoder();
      return encoder.encode(raw);
    } catch (Exception se) {
      throw new Exception("Exception while encoding " + se);
    }

  }

  public String decode(String in) {
    throw new RuntimeException("NOT SUPPORTED");
  }

  /**
   * Test harness
   * @param args
   */
  public static void main(String[] args) {
     String clearText = "apple";
    try {
      MD5Sample app = new MD5Sample();
      String encryptedHash = app.encode(clearText);
      System.out.println(encryptedHash);
    } catch (Exception e) {
      e.printStackTrace();
    }

  }
}