Numdroid - ASIS CTF Finals 2014

ArrayTools.java

package io.asis.ctf2014.numdriod.tools;

import java.util.*;

public class ArrayTools
{
    public static Integer[] Range(final int n, final int n2) {
        final Integer[] array = new Integer[n2 - n];
        for (int i = 0; i < array.length; ++i) {
            array[i] = n + i;
        }
        return array;
    }
    
    public static <T> void each(final List<T> list, final EachAction<T> eachAction) {
        final Iterator<T> iterator = list.iterator();
        while (iterator.hasNext()) {
            eachAction.action((T)((Object)iterator.next()));
        }
    }
    
    public static <T> void each(final T[] array, final EachAction<T> eachAction) {
        for (int length = array.length, i = 0; i < length; ++i) {
            eachAction.action(array[i]);
        }
    }
    
    public static <T> void each_with_index(final T[] array, final EachIndexAction<T> eachIndexAction) {
        for (int i = 0; i < array.length; ++i) {
            eachIndexAction.action(i, array[i]);
        }
    }
    
    public static <T, S> List<S> map(final List<T> list, final MapAction<T, S> mapAction) {
        final ArrayList<?> list2 = new ArrayList<?>();
        final Iterator<T> iterator = list.iterator();
        while (iterator.hasNext()) {
            list2.add((Object)mapAction.action((T)((Object)iterator.next())));
        }
        return list2;
    }
    
    public static <T, S> List<S> map(final T[] array, final MapAction<T, S> mapAction) {
        final ArrayList<?> list = new ArrayList<?>();
        for (int length = array.length, i = 0; i < length; ++i) {
            list.add((Object)mapAction.action(array[i]));
        }
        return list;
    }
    
    public static <T> List<T> select(final List<T> list, final SelectAction<T> selectAction) {
        final ArrayList<?> list2 = new ArrayList<?>();
        for (final T t : list) {
            if (selectAction.action(t)) {
                list2.add((Object)t);
            }
        }
        return list2;
    }
    
    public static <T> List<T> select(final T[] array, final SelectAction<T> selectAction) {
        final ArrayList<?> list = new ArrayList<?>();
        for (final T t : array) {
            if (selectAction.action(t)) {
                list.add((Object)t);
            }
        }
        return list;
    }
}

Verify.java

package io.asis.ctf2014.numdriod;

import java.security.*;
import java.util.*;
import android.content.*;
import io.asis.ctf2014.numdriod.tools.*;

public class Verify
{
    private static String OneWayFunction(final String s) {
        final MessageDigest instance;
        final byte[] digest;
        final List<Object> map = ArrayTools.map(ArrayTools.select((List<Object>)ArrayTools.map(new String[] { "MD2", "MD5", "SHA-1", "SHA-256", "SHA-384", "SHA-512" }, (MapAction<String, S>)new MapAction<String, byte[]>() {
            public byte[] action(final String algorithm) {
                final byte[] digest;
                try {
                    final MessageDigest instance = MessageDigest.getInstance(algorithm);
                    instance.update(s.getBytes());
                    digest = instance.digest();
                }
                catch (NoSuchAlgorithmException ex) {
                    return null;
                }
                return digest;
            }
        }), (SelectAction<Object>)new SelectAction<byte[]>() {
            public boolean action(final byte[] array) {
                return array != null;
            }
        }), (MapAction<Object, Object>)new MapAction<byte[], byte[]>() {
            public byte[] action(final byte[] array) {
                final byte[] array2 = new byte[8];
                for (int i = 0; i < array2.length / 2; ++i) {
                    array2[i] = array[i];
                }
                for (int j = 0; j < array2.length / 2; ++j) {
                    array2[j + array2.length / 2] = array[-2 + (array.length - j)];
                }
                return array2;
            }
        });
        final byte[] input = new byte[8 * map.size()];
        for (int i = 0; i < input.length; ++i) {
            input[i] = ((byte[])((Object)map.get(i % map.size())))[i / map.size()];
        }
        final StringBuilder sb;
        final int length;
        try {
            instance = MessageDigest.getInstance("MD5");
            instance.update(input);
            digest = instance.digest();
            sb = new StringBuilder();
            length = digest.length;
        }
        catch (NoSuchAlgorithmException) {
            return "";
        }
        int j = 0;
        while (j < length) {
            while (true) {
                Object hexString = null;
                try {
                    hexString = Integer.toHexString(255 & digest[j]);
                }
                catch (NoSuchAlgorithmException) {}
                Label_0190: {
                    final String string;
                    Label_0213: {
                        try {
                            if (((String)hexString).length() < 2) {
                                break Label_0213;
                            }
                            sb.append((String)hexString);
                        }
                        catch (NoSuchAlgorithmException) {}
                        ++j;
                        break;
                        try {
                            string = "0" + (String)hexString;
                        }
                        catch (NoSuchAlgorithmException) {}
                    }
                    
                    hexString = string;
                    break Label_0190;
                }
                
            }
        }
        final String string2;
        try {
            string2 = sb.toString();
        }
        catch (NoSuchAlgorithmException) {}
        return string2;
    }
    
    public static boolean isOk(final Context context, final String s) {
        String substring = s;
        if (s.length() > 7) {
            substring = s.substring(0, 7);
        }
        final String oneWayFunction = OneWayFunction(substring);
        DebugTools.log("digest: " + substring + " => " + oneWayFunction);
        final boolean equals = oneWayFunction.equals("be790d865f2cea9645b3f79c0342df7e");
        boolean b = false;
        if (equals) {
            b = true;
        }
        return b;
    }
}