Discuz! is a forum software developed by Comsenz. authcode is a function that able to encrypt the string into human unreadable form and also can decrypt it. The beauty inside is how many times you make encryption, the encrypted string is not same at all, but when you make decryption it is able to change back to original string. Comsenz had made great contribution to the PHP world by authcode function, whereas nowadays many of the PHP developers are using authcode function in their project, even me.

Now, I would like to find some way using Java to manipulate authcode function. However my skill is not talentable from getting authcode function works. Therefore, I searched online and found that the post rain.xie posted on Javaeye Forum. I changed a little bit from there to be hosted on Google Appengine along with my project. Notice that the implementation of Base64 Decoder I am using Google Appengine Library API.

Here is the code:

AuthCode.java

package com.fyhao.gift.helper;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Calendar;
import java.util.Random;
import com.google.appengine.repackaged.com.google.common.util.Base64;

public class AuthCode {

    public enum DiscuzAuthcodeMode {
        Encode, Decode
    };

    public static String CutString(String str, int startIndex, int length) {
        if (startIndex >= 0) {
            if (length < 0) {
                length = length * -1;
                if (startIndex – length < 0) {
                    length = startIndex;
                    startIndex = 0;
                } else {
                    startIndex = startIndex – length;
                }
            }

            if (startIndex > str.length()) {
                return "";
            }

        } else {
            if (length < 0) {
                return "";
            } else {
                if (length + startIndex > 0) {
                    length = length + startIndex;
                    startIndex = 0;
                } else {
                    return "";
                }
            }
        }

        if (str.length() – startIndex < length) {

            length = str.length() – startIndex;
        }

        return str.substring(startIndex, startIndex + length);
    }

    public static String CutString(String str, int startIndex) {
        return CutString(str, startIndex, str.length());
    }

    public static String MD5(String pass) {
        byte[] defaultBytes = pass.getBytes();
        try{
             MessageDigest algorithm = MessageDigest.getInstance("MD5");
             algorithm.reset();
             algorithm.update(defaultBytes);
             byte messageDigest[] = algorithm.digest();

             StringBuffer hexString = new StringBuffer();
             for (int i=0;i<messageDigest.length;i++) {
            String hex = Integer.toHexString(0xFF & messageDigest[i]);
            if(hex.length()==1)
            hexString.append(’0′);

            hexString.append(hex);
             }
             return hexString.toString();
        }
        catch(NoSuchAlgorithmException nsae){
        }

        return "";
    }

    public static boolean StrIsNullOrEmpty(String str) {
        //#if NET1
        if (str == null || str.trim().equals("")) {
            return true;
        }

        return false;
    }

    static private byte[] GetKey(byte[] pass, int kLen) {
        byte[] mBox = new byte[kLen];

        for (int i = 0; i < kLen; i++) {
            mBox[i] = (byte) i;
        }

        int j = 0;
        for (int i = 0; i < kLen; i++) {

            j = (j + (int) ((mBox[i] + 256) % 256) + pass[i % pass.length])
                    % kLen;

            byte temp = mBox[i];
            mBox[i] = mBox[j];
            mBox[j] = temp;
        }

        return mBox;
    }

    public static String RandomString(int lens) {
        char[] CharArray = { ‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’, ‘g’, ‘h’, ‘j’, ‘k’,
                ‘l’, ‘m’, ‘n’, ‘o’, ‘p’, ‘q’, ‘r’, ‘s’, ‘t’, ‘u’, ‘v’, ‘w’,
                ‘x’, ‘y’, ‘z’, ’0′, ’1′, ’2′, ’3′, ’4′, ’5′, ’6′, ’7′, ’8′, ’9′ };
        int clens = CharArray.length;
        String sCode = "";
        Random random = new Random();
        for (int i = 0; i < lens; i++) {
            sCode += CharArray[Math.abs(random.nextInt(clens))];
        }
        return sCode;
    }

    public static String authcodeEncode(String source, String key, int expiry) {
        return authcode(source, key, DiscuzAuthcodeMode.Encode, expiry);

    }

    public static String authcodeEncode(String source, String key) {
        return authcode(source, key, DiscuzAuthcodeMode.Encode, 0);

    }

    public static String authcodeDecode(String source, String key) {
        return authcode(source, key, DiscuzAuthcodeMode.Decode, 0);

    }

    private static String authcode(String source, String key,
            DiscuzAuthcodeMode operation, int expiry) {
        try {
            if (source == null || key == null) {
                return "";
            }

            int ckey_length = 4;
            String keya, keyb, keyc, cryptkey, result;

            key = MD5(key);

            keya = MD5(CutString(key, 0, 16));

            keyb = MD5(CutString(key, 16, 16));

            keyc = ckey_length > 0 ? (operation == DiscuzAuthcodeMode.Decode ? CutString(
                    source, 0, ckey_length)
                    : RandomString(ckey_length))
                    : "";

            cryptkey = keya + MD5(keya + keyc);

            if (operation == DiscuzAuthcodeMode.Decode) {
                byte[] temp;
                temp = Base64.decode(CutString(source, ckey_length));
                result = new String(RC4(temp, cryptkey));
                if (CutString(result, 10, 16).equals(CutString(MD5(CutString(result, 26) + keyb), 0, 16))) {
                    return CutString(result, 26);
                } else {
                    temp = Base64.decode(CutString(source+"=", ckey_length));
                    result = new String(RC4(temp, cryptkey));
                    if (CutString(result, 10, 16).equals(CutString(MD5(CutString(result, 26) + keyb), 0, 16))) {
                        return CutString(result, 26);
                    } else {
                        temp = Base64.decode(CutString(source+"==", ckey_length));
                        result = new String(RC4(temp, cryptkey));
                        if (CutString(result, 10, 16).equals(CutString(MD5(CutString(result, 26) + keyb), 0, 16))) {
                            return CutString(result, 26);
                        }else{
                            return "2";
                        }
                    }
                }
            } else {
                source = "0000000000" + CutString(MD5(source + keyb), 0, 16)
                        + source;

                byte[] temp = RC4(source.getBytes("GBK"), cryptkey);

                return keyc + Base64.encode(temp);

            }
        } catch (Exception e) {
            return "";
        }

    }

    private static byte[] RC4(byte[] input, String pass) {
        if (input == null || pass == null)
            return null;

        byte[] output = new byte[input.length];
        byte[] mBox = GetKey(pass.getBytes(), 256);

        int i = 0;
        int j = 0;

        for (int offset = 0; offset < input.length; offset++) {
            i = (i + 1) % mBox.length;
            j = (j + (int) ((mBox[i] + 256) % 256)) % mBox.length;

            byte temp = mBox[i];
            mBox[i] = mBox[j];
            mBox[j] = temp;
            byte a = input[offset];

            byte b = mBox[(toInt(mBox[i]) + toInt(mBox[j])) % mBox.length];

            output[offset] = (byte) ((int) a ^ (int) toInt(b));
        }

        return output;
    }

    public static int toInt(byte b) {
        return (int) ((b + 256) % 256);
    }

    public long getUnixTimestamp() {
        Calendar cal = Calendar.getInstance();
        return cal.getTimeInMillis() / 1000;
    }

}