Lula's Chronicles

Android SDK Manager can't find latest updates!

2012-11-14T10:26:00.001-05:00

I had a nice surprise today. After updating the ADT plugin in Eclipse it says that I must update the android tools.

Ok, one more time I opened the SDK Manager and searched for the updates. But wait... there is no updates. And Eclipse doesn't work! WTF?

"It must be a bad nightmare, take it easy" I think. Just do the obvious thing, close the SDK Manager and open it again. Stupid solution, it doesn't work.

Ok, something is bad, so I enter to the preferences and what I see is "Cache size" with the option "Delete cache". Oh yea! Now it works. God exists.

Stupid cache, you think you know everything, but I am better than you :D

Development tools I can't live without

2012-11-06T03:03:00.002-05:00

Every developer has his own set of preferred tools. Me too. In my case all these tools are Java oriented because is the language I use more often. Obviously these are not the best tools you can find on internet, I'm sure you use other tools better and you hate my tools, but they gave me so many satisfactions that I think my work can't be finished without them. Too bad uh?

Eclipse: "naaaaaaaaaaa, no way" maybe you think. I understand people complaining this fantastic IDE, but I am in love with this tool. I tried all IntelliJ, Netbeans, etc. and I think I know Eclipse so well that I can face any problem that it can have, I accept it's buggy due to the free plugins we install all the time.
Findbugs: great free tool to detect common programming problems.
CheckStyle: the best tool to detect coding standard violations. I use it inside Eclipse of course.
UCDetector: Unused Code Detector. When your project it's really big you notice a lot of code that it is not being used. You can remove it automatically with proguard, but the best option is to delete it. Less code, less problems. This free Eclipse plugin will do the hard work for you, with many options, and allowing to remove multiple things with quickfix.
ASM Bytecode Plugin: amazing plugin to see the java bytecode in real time. Sometimes when you want to improve something it is good to check the bytecode, you will get some nice surprises. You can change the code, but the bytecode could be exactly the same or even worst.
Lint: checks for problems in Android projects. It is included in the android SDK and the ADT plugin.
Total Commander: wtf? This is not for java. Of course not, it is only THE file commander. Extremely powerful, and with lot of free plugins. It's for windows only but I use it with "wine" in MacOS. If you create a plugin the author will send you a personal license for free! Thanks Ghisler, you made me happy on christmas ;)
Sonar: easily receive reports with code coverage and errors.
PlantUML: combined with Javadoc is an amazing tool to add UML graphs to your documentation.
Google: do I need to put the link? When you don't know something he knows it :D

And the last thing I can say is: use the tools that are more comfortable for you, and use them well and wisely. You will love your daily job.

Cheers,

Lula

What I want to see in Logcat plugin for Eclipse

2011-10-19T13:55:00.001-04:00

The new logcat plugin is cool, now has regex and more options to filter. But it lacks of:

highlight searched text
syntax coloring for XML and others
selection of log format (brief, full, etc.) and ring buffer (main, radio, events)

I developed a small logcat plugin with those both features. Warning, this logcat plugin is ugly (I'm not a UI designer), it's just a small example.

You can download it here: https://skydrive.live.com/redir.aspx?cid=511e6cc6d535b08d&resid=511E6CC6D535B08D!123

A few screenshots

highlight searched text in yellow

syntax highlight in XML

I will continue using the original logcat plugin, is really great, but still has many things to improve. Congratulations to all the developers, they did a great job.

BR,

Lula

Another option to disassemble APK files

2011-08-31T11:10:00.002-04:00

http://code.google.com/p/dex2jar/

I didn't tested it, just found the project.

BR,

Lula

New DEX disassembler

2011-08-31T11:05:00.003-04:00

Checkout this new DEX file disassembler

https://code.google.com/p/smali/

it looks good and has lots of options

BR,

Lula

Obfuscate android builds using proguard

2011-05-31T14:15:00.000-04:00

The new android SDK comes with proguard included in the build system. You can check how to use it at http://developer.android.com/guide/developing/tools/proguard.html

Not all the proguard options can be used, specially those used for optimizations.

You should keep all classes used in xml files. The best way to do it is to keep classes that extend from android.content.Context due to almost everything related to android UI and services belong to the android context.

After some research I give you the best proguard.cfg for almost any application.

-dontpreverify
-dontskipnonpubliclibraryclasses
-dontskipnonpubliclibraryclassmembers
-optimizations !code/simplification/arithmetic
-optimizationpasses 5
-useuniqueclassmembernames
-dontusemixedcaseclassnames
-verbose
-target 1.6
# -repackageclasses mypackage

-keep public class * extends android.content.Context {
*** (...);
}

-keepclassmembers enum * {
    public static **[] values();
    public static ** valueOf(java.lang.String);
}

-keepattributes Exceptions, InnerClasses, Signature

# Keep names - Native method names. Keep all native class/method names.
-keepclasseswithmembers,allowshrinking class * {
    native ;
}

-assumenosideeffects public class android.util.Log {
*** *(...);
}

# Remove - System method calls. Remove all invocations of System
# methods without side effects whose return values are not used.
-assumenosideeffects public class java.lang.System {
    public static long currentTimeMillis();
    static java.lang.Class getCallerClass();
    public static int identityHashCode(java.lang.Object);
    public static java.lang.SecurityManager getSecurityManager();
    public static java.util.Properties getProperties();
    public static java.lang.String getProperty(java.lang.String);
    public static java.lang.String getenv(java.lang.String);
    public static java.lang.String mapLibraryName(java.lang.String);
    public static java.lang.String getProperty(java.lang.String,java.lang.String);
}

# Remove - Math method calls. Remove all invocations of Math
# methods without side effects whose return values are not used.
-assumenosideeffects public class java.lang.Math {
    public static double sin(double);
    public static double cos(double);
    public static double tan(double);
    public static double asin(double);
    public static double acos(double);
    public static double atan(double);
    public static double toRadians(double);
    public static double toDegrees(double);
    public static double exp(double);
    public static double log(double);
    public static double log10(double);
    public static double sqrt(double);
    public static double cbrt(double);
    public static double IEEEremainder(double,double);
    public static double ceil(double);
    public static double floor(double);
    public static double rint(double);
    public static double atan2(double,double);
    public static double pow(double,double);
    public static int round(float);
    public static long round(double);
    public static double random();
    public static int abs(int);
    public static long abs(long);
    public static float abs(float);
    public static double abs(double);
    public static int max(int,int);
    public static long max(long,long);
    public static float max(float,float);
    public static double max(double,double);
    public static int min(int,int);
    public static long min(long,long);
    public static float min(float,float);
    public static double min(double,double);
    public static double ulp(double);
    public static float ulp(float);
    public static double signum(double);
    public static float signum(float);
    public static double sinh(double);
    public static double cosh(double);
    public static double tanh(double);
    public static double hypot(double,double);
    public static double expm1(double);
    public static double log1p(double);
}

# Remove - Number method calls. Remove all invocations of Number
# methods without side effects whose return values are not used.
-assumenosideeffects public class java.lang.* extends java.lang.Number {
    public static java.lang.String toString(byte);
    public static java.lang.Byte valueOf(byte);
    public static byte parseByte(java.lang.String);
    public static byte parseByte(java.lang.String,int);
    public static java.lang.Byte valueOf(java.lang.String,int);
    public static java.lang.Byte valueOf(java.lang.String);
    public static java.lang.Byte decode(java.lang.String);
    public int compareTo(java.lang.Byte);
    public static java.lang.String toString(short);
    public static short parseShort(java.lang.String);
    public static short parseShort(java.lang.String,int);
    public static java.lang.Short valueOf(java.lang.String,int);
    public static java.lang.Short valueOf(java.lang.String);
    public static java.lang.Short valueOf(short);
    public static java.lang.Short decode(java.lang.String);
    public static short reverseBytes(short);
    public int compareTo(java.lang.Short);
    public static java.lang.String toString(int,int);
    public static java.lang.String toHexString(int);
    public static java.lang.String toOctalString(int);
    public static java.lang.String toBinaryString(int);
    public static java.lang.String toString(int);
    public static int parseInt(java.lang.String,int);
    public static int parseInt(java.lang.String);
    public static java.lang.Integer valueOf(java.lang.String,int);
    public static java.lang.Integer valueOf(java.lang.String);
    public static java.lang.Integer valueOf(int);
    public static java.lang.Integer getInteger(java.lang.String);
    public static java.lang.Integer getInteger(java.lang.String,int);
    public static java.lang.Integer getInteger(java.lang.String,java.lang.Integer);
    public static java.lang.Integer decode(java.lang.String);
    public static int highestOneBit(int);
    public static int lowestOneBit(int);
    public static int numberOfLeadingZeros(int);
    public static int numberOfTrailingZeros(int);
    public static int bitCount(int);
    public static int rotateLeft(int,int);
    public static int rotateRight(int,int);
    public static int reverse(int);
    public static int signum(int);
    public static int reverseBytes(int);
    public int compareTo(java.lang.Integer);
    public static java.lang.String toString(long,int);
    public static java.lang.String toHexString(long);
    public static java.lang.String toOctalString(long);
    public static java.lang.String toBinaryString(long);
    public static java.lang.String toString(long);
    public static long parseLong(java.lang.String,int);
    public static long parseLong(java.lang.String);
    public static java.lang.Long valueOf(java.lang.String,int);
    public static java.lang.Long valueOf(java.lang.String);
    public static java.lang.Long valueOf(long);
    public static java.lang.Long decode(java.lang.String);
    public static java.lang.Long getLong(java.lang.String);
    public static java.lang.Long getLong(java.lang.String,long);
    public static java.lang.Long getLong(java.lang.String,java.lang.Long);
    public static long highestOneBit(long);
    public static long lowestOneBit(long);
    public static int numberOfLeadingZeros(long);
    public static int numberOfTrailingZeros(long);
    public static int bitCount(long);
    public static long rotateLeft(long,int);
    public static long rotateRight(long,int);
    public static long reverse(long);
    public static int signum(long);
    public static long reverseBytes(long);
    public int compareTo(java.lang.Long);
    public static java.lang.String toString(float);
    public static java.lang.String toHexString(float);
    public static java.lang.Float valueOf(java.lang.String);
    public static java.lang.Float valueOf(float);
    public static float parseFloat(java.lang.String);
    public static boolean isNaN(float);
    public static boolean isInfinite(float);
    public static int floatToIntBits(float);
    public static int floatToRawIntBits(float);
    public static float intBitsToFloat(int);
    public static int compare(float,float);
    public boolean isNaN();
    public boolean isInfinite();
    public int compareTo(java.lang.Float);
    public static java.lang.String toString(double);
    public static java.lang.String toHexString(double);
    public static java.lang.Double valueOf(java.lang.String);
    public static java.lang.Double valueOf(double);
    public static double parseDouble(java.lang.String);
    public static boolean isNaN(double);
    public static boolean isInfinite(double);
    public static long doubleToLongBits(double);
    public static long doubleToRawLongBits(double);
    public static double longBitsToDouble(long);
    public static int compare(double,double);
    public boolean isNaN();
    public boolean isInfinite();
    public int compareTo(java.lang.Double);
    public (byte);
    public (short);
    public (int);
    public (long);
    public (float);
    public (double);
    public (java.lang.String);
    public byte byteValue();
    public short shortValue();
    public int intValue();
    public long longValue();
    public float floatValue();
    public double doubleValue();
    public int compareTo(java.lang.Object);
    public boolean equals(java.lang.Object);
    public int hashCode();
    public java.lang.String toString();
}

# Remove - String method calls. Remove all invocations of String
# methods without side effects whose return values are not used.
-assumenosideeffects public class java.lang.String {
    public ();
    public (byte[]);
    public (byte[],int);
    public (byte[],int,int);
    public (byte[],int,int,int);
    public (byte[],int,int,java.lang.String);
    public (byte[],java.lang.String);
    public (char[]);
    public (char[],int,int);
    public (java.lang.String);
    public (java.lang.StringBuffer);
    public static java.lang.String copyValueOf(char[]);
    public static java.lang.String copyValueOf(char[],int,int);
    public static java.lang.String valueOf(boolean);
    public static java.lang.String valueOf(char);
    public static java.lang.String valueOf(char[]);
    public static java.lang.String valueOf(char[],int,int);
    public static java.lang.String valueOf(double);
    public static java.lang.String valueOf(float);
    public static java.lang.String valueOf(int);
    public static java.lang.String valueOf(java.lang.Object);
    public static java.lang.String valueOf(long);
    public boolean contentEquals(java.lang.StringBuffer);
    public boolean endsWith(java.lang.String);
    public boolean equalsIgnoreCase(java.lang.String);
    public boolean equals(java.lang.Object);
    public boolean matches(java.lang.String);
    public boolean regionMatches(boolean,int,java.lang.String,int,int);
    public boolean regionMatches(int,java.lang.String,int,int);
    public boolean startsWith(java.lang.String);
    public boolean startsWith(java.lang.String,int);
    public byte[] getBytes();
    public byte[] getBytes(java.lang.String);
    public char charAt(int);
    public char[] toCharArray();
    public int compareToIgnoreCase(java.lang.String);
    public int compareTo(java.lang.Object);
    public int compareTo(java.lang.String);
    public int hashCode();
    public int indexOf(int);
    public int indexOf(int,int);
    public int indexOf(java.lang.String);
    public int indexOf(java.lang.String,int);
    public int lastIndexOf(int);
    public int lastIndexOf(int,int);
    public int lastIndexOf(java.lang.String);
    public int lastIndexOf(java.lang.String,int);
    public int length();
    public java.lang.CharSequence subSequence(int,int);
    public java.lang.String concat(java.lang.String);
    public java.lang.String replaceAll(java.lang.String,java.lang.String);
    public java.lang.String replace(char,char);
    public java.lang.String replaceFirst(java.lang.String,java.lang.String);
    public java.lang.String[] split(java.lang.String);
    public java.lang.String[] split(java.lang.String,int);
    public java.lang.String substring(int);
    public java.lang.String substring(int,int);
    public java.lang.String toLowerCase();
    public java.lang.String toLowerCase(java.util.Locale);
    public java.lang.String toString();
    public java.lang.String toUpperCase();
    public java.lang.String toUpperCase(java.util.Locale);
    public java.lang.String trim();
}

# Remove - StringBuffer method calls. Remove all invocations of StringBuffer
# methods without side effects whose return values are not used.
-assumenosideeffects public class java.lang.StringBuffer {
    public ();
    public (int);
    public (java.lang.String);
    public (java.lang.CharSequence);
    public java.lang.String toString();
    public char charAt(int);
    public int capacity();
    public int codePointAt(int);
    public int codePointBefore(int);
    public int indexOf(java.lang.String,int);
    public int lastIndexOf(java.lang.String);
    public int lastIndexOf(java.lang.String,int);
    public int length();
    public java.lang.String substring(int);
    public java.lang.String substring(int,int);
}

# Remove - StringBuilder method calls. Remove all invocations of StringBuilder
# methods without side effects whose return values are not used.
-assumenosideeffects public class java.lang.StringBuilder {
    public ();
    public (int);
    public (java.lang.String);
    public (java.lang.CharSequence);
    public java.lang.String toString();
    public char charAt(int);
    public int capacity();
    public int codePointAt(int);
    public int codePointBefore(int);
    public int indexOf(java.lang.String,int);
    public int lastIndexOf(java.lang.String);
    public int lastIndexOf(java.lang.String,int);
    public int length();
    public java.lang.String substring(int);
    public java.lang.String substring(int,int);
}

BR,

Lula

How to check if an APK has the flag android:debuggable="true"

2011-04-26T16:37:00.000-04:00

Using the aapt tool you can check lots of things inside an apk. Use the following command:

aapt list -v -a myfile.apk

this shows hundreds of lines, but you must search the following text "android:debuggable"

this flag can have the values:

0x0: debuggable false
0xffffffff: debugabble true

in my case the entire line is the following

A: android:debuggable(0x0101000f)=(type 0x12)0xffffffff

Ups! My release build had the flag enabled ;)

Cheers,

Lula

Proguard 4.x error - java.lang.ArrayIndexOutOfBoundsException - How to fix it

2010-03-02T18:29:00.000-05:00

Using Proguard to obfuscate your classes in your midlets is a must. The jar size is reduced and the code is optimized.

But when I obfuscated my app an error is displayed and the jar is not obfustaced. The error is similar to:

java.lang.ArrayIndexOutOfBoundsException: 2

WTF is this? :)

I don't know why, I didn't download the source of proguard (BTW this amazing tool is opensource)

How to fix it? Two options:
* disable optimization. It's not the best option but it helps. Use parameter -dontoptimize
* disable optimization partially. I used this option. The last proguard has many parameters for optimization, and I found the parameter that worked in my midlet:

-optimizations !method/marking/static

this means the optimizer will avoid marking methods as static.

It worked for me, I hope it works for you.

Proguard optimizations site: http://proguard.sourceforge.net/manual/optimizations.html

Samsung - Java Error: Invalid Format. How to fix it.

2010-03-02T18:17:00.001-05:00

There is a strange error in Samsung phones. When you try to launch a midlet the phone displays the message "Java Error: Invalid format".

Why?

This means the virtual machine can't load the classes of the midlet. It could be:
- the classes are not preverified
- the classes are corrupted
- the classes are ok but the VM can't load them, because an exception is launched while they are loading..

We will focus in the last option. Why a class can't be loaded and how to fix it?

- Sometimes we write some lines of code in the midlet constructor. But this lines can have method calls to other classes and so on, and all classes must be loaded BEFORE the midlet is initializad. If the midlet is not initialized it can't manage well things like screen.getWidth and getHeight, etc. Avoid method calls in the midlet constructor.
- Other cause can be to write method calls in static blocks or static variables. It's the same problem than before, lots of things must be loaded BEFORE the midlet is instantiated.

So, now the midlet is instantiated before the classes are loaded. Now the error "Invalid Formatd" shouldn't appear. Your phone must launch now an exception or anything similar.

E.g: Samsung S8000 Jet. This phone has a problem in some firmwares. The method Font.getSize() returns a non standard value, and when you want to obtain a new font using the size returned by Font.getSize() an exception is launched. If this code is called by the constructor block an exception is thrown before the midlet is instantiated, so the error "Invalid Format" is displayed.

I worked with lots of samsungs and generally the solution is the same. Avoid coding in the constructor to find easily the errors.

I hope it works for you.

Cheers,

Lula

Bug Sony W580: error displaying text using UTF8 encoding

2010-02-27T00:27:00.002-05:00

There is a strange bug with SonyEricsson W580. When drawing strings in UTF8 format some special characters are not displayed.
The strings are created using the following:

new String(bytearray, offset, size, "UTF-8")

and to fix the bug it must be created using:

                StringBuffer sb = new StringBuffer();
                for (int i = offset; i < offset + size; i++) {
                    sb.append(new String(bytearray, i, bytearray[i] < 0 ? 2 : 1, "UTF-8"));
                    if (bytearray[i] < 0){ i++; }
                }
                String txt = sb.toString();

A tiny bug, and a very ugly fix ;)

Lula

Java Class unpacker v0.7.1 released

2009-12-10T21:41:00.000-05:00

Java Class Unpacker v0.7.1 released.
Plugin for Total Commander

Changes:
* fixed LDC_W opcode
* fixed MULTIANEWARRAY opcode
* fixed GOTO_W opcode
* fixed NEWARRAY opcode
- refactoring
- implemented basic configuration
- fixed char type in constant pool

Download: http://cid-511e6cc6d535b08d.skydrive.live.com/self.aspx/JavaClassUnpacker

Cheers,

Lula

Java Class Unpacker v0.7.0

2009-12-01T09:42:00.000-05:00

Java Class Unpacker v0.7.0 released.
Plugin for Total Commander

Changes:
- fixed NEW opcode
- fixed error with classes containing many attribute types: SourceFile, ConstantValue, Exceptions, InnerClasses, Synthetic, LineNumberTable, LocalVariableTable, Deprecated,
- fixed native methods
+ added header.txt in class unpack containing class header info
- fixed locals and stack size in method unpack
- fixed integer, long, float and double in constant pool

Download: http://cid-511e6cc6d535b08d.skydrive.live.com/self.aspx/JavaClassUnpacker

Cheers,

Lula

Java Class Unpacker v0.6.0

2009-11-27T22:24:00.001-05:00

Java Class Unpacker v0.6.0 released.
Plugin for Total Commander

Changes:
- fixed: abstract classes and methods
- added constant pool
- implemented decompilation of tableswitch and lookupswitch
- file offsets and hexa bytes in code
- renamed file to JavaClassUnpacker.wcx

Download: http://cid-511e6cc6d535b08d.skydrive.live.com/self.aspx/JavaClassUnpacker

Cheers,

Lula

New Total Commander Plugin - Java Class Unpacker v0.5.0

2009-11-26T23:53:00.000-05:00

I developed a new plugin for the amazing Total Commander. Using this plugin you can enter to class files as compressed files and see fields and methods as files.
Methods can be viewed using F3, the java bytecode is displayed as text.

I have no site so I uploaded to megaupload, you can download it from:

http://www.megaupload.com/?d=8BW30ZAD

Please feel free to send me bugs, comments or suggestions.

Enjoy!

J2ME: Fixing Cannot find class java/lang/NoClassDefFoundError at preverify

2009-11-13T09:34:00.000-05:00

I had a strange error when preverifying a midlet.

     [exec] Error preverifying class temp.TestMidlet
     [exec]     VERIFIER ERROR temp/TestMidlet.()V:
     [exec] Cannot find class java/lang/NoClassDefFoundError

The midlet is ok, Eclipse doesn't display an error. Searching in all the library jars in WTK I found the class NoClassDefFoundError is inside cldcapi11.jar. I modified the cldc jar and nows compiles.

But is not enough for me, I'm not using float or doubles so I want to compile the midlet for CLDC10. So I continued playing and I found the reason: I'm using the field named "class" to obtain the name of a class.

E.g:

To obtain the Class object of class TestMidlet I'm using the following code:

Class clazz = TestMidlet.class;

this is ok for CLDC11 but for CLDC10 is wrong, I must use this.getClass or something similar.

I hope you can find this useful.

Cheers,

Lula

All mobile developer sites

2009-11-13T07:47:00.001-05:00

Just for reference, I'm writing here all developer sites useful for mobile frikis:

Java Mobile
http://developers.sun.com/mobility

Sony
http://developer.sonyericsson.com

Motorola
http://developer.motorola.com

Nokia
http://www.nokia.com/developers

Samsung
http://innovator.samsungmobile.com

IPhone
http://developer.apple.com/iphone

Android
http://developer.android.com

Blackberry
http://na.blackberry.com/eng/developers

BREW
http://brew.qualcomm.com/brew/en/developer/overview.html

HTC
http://developer.htc.com

Windows Mobile
http://developer.windowsmobile.com
http://msdn.microsoft.com/en-us/windowsmobile/default.aspx

OpenGL ES
http://www.khronos.org/opengles

Let's go mobile!

Cheers,

Lula

Convert Android DEX to Java

2009-11-10T10:28:00.000-05:00

I'm playing with a great Android to Java converter named UnDX. You can find it at

http://www.illegalaccess.org/undx

it uses BCEL to convert the files. It's in beta, has some errors.

So, I decided to create my own converter using ASM. The idea is simple:

- Create a DEX reader extending ClassReader. Here call all the Visitor events to generate the java code.
- Use ASM to manipulate the java bytecode.
- Create a DEX ClassWriter. It must be exactly the same for java, but after generating all the bytearrays it must use dx command to create de DEX file.

The idea is simple, I had some tests and it works! I'm generating the java code and I can manipulate it.

I'll tell you later what happens with some big DEX files.

Cheers,

Lula

How to manipulate bytecode in android

2009-11-05T00:04:00.001-05:00

The following was tested successfully in Android SDK 1.1 and 2.0

Step 1: Create an android project in eclipse

Step 2: open the activity class and change the event onCreate with the following

boolean flag = false;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TextView tv = new TextView(this);
if(flag){
tv.setText("CONGRATS! YOU CRACKED MY CODE! ;)");
} else{
tv.setText("NOT CRACKED YET... :(");
}
setContentView(tv);
}

Check the new variable named flag, it is our main objective.

Step 3: run the project in the emulator, you will see a screen showing the text "NOT CRACKED YET... :("

Step 4: go to the folder YOUR_PROJECT\bin and remove the signature from the APK file. If you don't know how to do it read my previous entry here

Step 5

disassemble the file classes.dex. If you don't know how to do it read my previous entry here.
Search the text "onCreate" to find the body of the onCreate method. You will find something like this:

Virtual methods -
#0 : (in La/a/Start;)
name : 'onCreate'
type : '(Landroid/os/Bundle;)V'
access : 0x0001 (PUBLIC)
code -
registers : 4
ins : 2
outs : 2
insns size : 27 16-bit code units
0003c4: |[0003c4] a.a.Start.onCreate:(Landroid/os/Bundle;)V
0003d4: 6f20 0900 3200 |0000: invoke-super {v2, v3}, Landroid/app/Activity;.onCreate:(Landroid/os/Bundle;)V // method@0009
0003da: 2200 0b00 |0003: new-instance v0, Landroid/widget/TextView; // class@000b
0003de: 7020 0a00 2000 |0005: invoke-direct {v0, v2}, Landroid/widget/TextView;.:(Landroid/content/Context;)V // method@000a
0003e4: 5521 0400 |0008: iget-boolean v1, v2, La/a/Start;.flag:Z // field@0004
0003e8: 3801 0b00 |000a: if-eqz v1, 0015 // +000b
0003ec: 1a01 0100 |000c: const-string v1, "CONGRATS! YOU CRACKED MY CODE! ;)" // string@0001
0003f0: 6e20 0b00 1000 |000e: invoke-virtual {v0, v1}, Landroid/widget/TextView;.setText:(Ljava/lang/CharSequence;)V // method@000b
0003f6: 6e20 0700 0200 |0011: invoke-virtual {v2, v0}, La/a/Start;.setContentView:(Landroid/view/View;)V // method@0007
0003fc: 0e00 |0014: return-void
0003fe: 1a01 1300 |0015: const-string v1, "NOT CRACKED YET... :(" // string@0013
000402: 6e20 0b00 1000 |0017: invoke-virtual {v0, v1}, Landroid/widget/TextView;.setText:(Ljava/lang/CharSequence;)V // method@000b
000408: 28f7 |001a: goto 0011 // -0009
catches : (none)
positions :
0x0000 line=15
0x0003 line=16
0x0008 line=17
0x000c line=18
0x0011 line=22
0x0014 line=23
0x0015 line=20
locals :
0x0008 - 0x001b reg=0 tv Landroid/widget/TextView;
0x0000 - 0x001b reg=2 this La/a/Start;
0x0000 - 0x001b reg=3 savedInstanceState Landroid/os/Bundle;

You need to understand how bytecode works. If you don't have any experience with bytecode manipulation please stop here.
I marked in red the line we want to change, because it is a jump that involves the lines of code showing texts. We must invert the jump so the screen will display another text.
edit in hexadecimal the file classes.dex and go to the offset 03E8, you will se the hex numbers 38 01 0b 00
Why? Check the following line:

0003e8: 3801 0b00 |000a: if-eqz v1, 0015 // +000b

the first number is the offset in the classes.dex file, the following numbers are the opcode and parameters.
If you check the opcode numbers HERE you can see the value 0x38 is for the opcode if-eqz, we must change this opcode to if-nez to invert the jump. Checking the opcodes list we see the value for if-nez is 0x39, so change the 38 value at offset 0x3E8 by 39
Now you must fix the checksum or you will have errors when installing the app. You can calculate the checksum with the following code:

public class FixDEXChecksum(){

/**
* Calculates the checksum for the .dex file in the
* given array, and modify the array to contain it.
*
* @param bytes non-null; the bytes of the file
*/
private static void calcChecksum(byte[] bytes) {
Adler32 a32 = new Adler32();

a32.update(bytes, 12, bytes.length - 12);

int sum = (int) a32.getValue();

bytes[8] = (byte) sum;
bytes[9] = (byte) (sum >> 8);
bytes[10] = (byte) (sum >> 16);
bytes[11] = (byte) (sum >> 24);
}

public static void main(String[] args) {
try {
File file = new File(args[0]);
FileInputStream fis = new FileInputStream(file);
byte[] data = new byte[fis.available()];
System.out.println("Reading DEX file");
fis.read(data);
System.out.println("Calculating new checksum");
calcChecksum(data);
fis.close();
System.out.println("Making backup");
file.renameTo(new File(args[0]+".bak"));
System.out.println("Writing new DEX file with checksum "+ Integer.toHexString(data[8]) +" "+ Integer.toHexString(data[9]) +" "+ Integer.toHexString(data[10]) +" "+ Integer.toHexString(data[11]));
FileOutputStream fos = new FileOutputStream(new File(args[0]));
fos.write(data);
fos.close();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}
}

Put the new classes.dex inside your unsigned APK
Sign the APK file again.
Run the program and voila! The text displayed is "CONGRATS! YOU CRACKED MY CODE! ;)"

I know it is a very small program and we know how the code works, but this is useful to see what can be done with bytecode manipulation.

Removing bytecode is not so simple, but you can try replacing the bytecode values in the lines you want to remove by zeros 00, it is the NOP bytecode.

Injecting bytecode is another story, lots of offsets must be modified in the classes.dex file. I will tell you later.

And I will test this in SDK 1.5, 1.6, but another day, i'm tired now :)

Enjoy!

How to check the signature in APK files or JAR files

2009-11-04T23:42:00.000-05:00

You can use the jarsigner tool from JDK.

JDKFOLDER\bin\jarsigner.exe -verify -verbose -certs myAndroidProgram.apk

or

JDKFOLDER\bin\jarsigner.exe -verify -verbose -certs myJavaProgram.jar

the output will be the list of files with a detail of the signature, as following:

sm 3366 Thu Nov 05 00:57:58 ART 2009 res/drawable/icon.png

X.509, CN=Android Debug, O=Android, C=US
[certificate is valid from 05/11/09 00:01 to 05/11/10 00:01]

sm 640 Thu Nov 05 00:57:58 ART 2009 res/layout/main.xml

X.509, CN=Android Debug, O=Android, C=US
[certificate is valid from 05/11/09 00:01 to 05/11/10 00:01]

sm 1248 Thu Nov 05 00:57:58 ART 2009 AndroidManifest.xml

X.509, CN=Android Debug, O=Android, C=US
[certificate is valid from 05/11/09 00:01 to 05/11/10 00:01]

sm 1012 Thu Nov 05 00:57:58 ART 2009 resources.arsc

X.509, CN=Android Debug, O=Android, C=US
[certificate is valid from 05/11/09 00:01 to 05/11/10 00:01]

sm 1984 Thu Nov 05 00:57:58 ART 2009 classes.dex

X.509, CN=Android Debug, O=Android, C=US
[certificate is valid from 05/11/09 00:01 to 05/11/10 00:01]

401 Thu Nov 05 00:57:58 ART 2009 META-INF/MANIFEST.MF
454 Thu Nov 05 00:57:58 ART 2009 META-INF/CERT.SF
771 Thu Nov 05 00:57:58 ART 2009 META-INF/CERT.RSA

s = signature was verified
m = entry is listed in manifest
k = at least one certificate was found in keystore
i = at least one certificate was found in identity scope

jar verified.

Cheers

Remove signature from APK file and sign it again

2009-11-04T23:32:00.000-05:00

The APK file is just a zip file with another extension. To remove the signature just unzip it, remove the folder META-INF and zip it again.

but how to sign it again? You can use your own signature or the debug signature used by Android SDK named debug.keystore

You can copy the debug signature from C:\Documents and Settings\\Local Settings\Application Data\Android\

The data of the signature is the following:

* Keystore name: "debug.keystore"
* Keystore password: "android"
* Key alias: "androiddebugkey"
* Key password: "android"
* CN: "CN=Android Debug,O=Android,C=US"

for more details go to http://developer.android.com/guide/publishing/app-signing.html

Now, how to sign the apk again? Use the jarsigner.exe tool, this tool comes with the JDK.

JDKFOLDER\bin\jarsigner.exe -verbose -storepass android -keystore debug.keystore myprogram.apk androiddebugkey

replace myprogram.apk with your own unsigned apk.

Is this useful? Maybe, if you want to modify the build with reverse engineering or something similar, use your imagination.

voila!

Disassemble dex files

2009-11-04T23:29:00.000-05:00

Android SDK comes with the tool dexdump.exe

To disassemble a dex file just use the following command:

dexdump.exe -d -f -h classes.dex >dexdump.txt

The output will be stored in the file dexdump.txt, and the format is dalvik bytecode, not java bytecode.

I will investigate how to modify this file.