ProGuardand DexGuard

for Optimizationand Protection

Eric LafortuneCreator of ProGuard and DexGuard

Technical director at Saikoa

Topics

ProGuard

– Techniques– Results

More application protection

– Goals– Attackers– Types of attacks– Protection

ProGuard

Applicationcode

Shrink

Libraries

Androidruntime

Optimize Obfuscate Processedcode

Androidruntime

Results

● Size reduction:

– Code (classes.dex): 20 … 90%– Application (.apk): 5 ... 70%

● Performance improvements: 0 … 20%

How to enable ProGuard?

Ant and Eclipse: project.properties

→ only applied when building release versions

# To enable ProGuard to shrink and obfuscate your code, uncomment this#proguard.config= ${sdk.dir}/tools/proguard/proguard-android.txt: proguard-project.txt

# To enable ProGuard to shrink and obfuscate your code, uncomment this#proguard.config= ${sdk.dir}/tools/proguard/proguard-android.txt: proguard-project.txt

Tip

How to enable ProGuard?

Gradle: build.gradle

→ completely flexible

android { buildTypes { release { runProguard true proguardFile getDefaultProguardFile('proguard-android.txt') } }

productFlavors { some_flavor { proguardFile 'proguard-project.txt' } }}

android { buildTypes { release { runProguard true proguardFile getDefaultProguardFile('proguard-android.txt') } }

productFlavors { some_flavor { proguardFile 'proguard-project.txt' } }}

New

Notes and warnings

“Closed-world assumption”

→ if debug build works fine,then ok to ignore in proguard-project.txt:

Warning: com.dropbox.client2.DropboxAPI: can't find referenced class org.json.simple.JSONArrayWarning: com.dropbox.client2.DropboxAPI: can't find referenced class org.json.simple.JSONArray

-dontwarn twitter4j.internal.logging.**-dontwarn com.dropbox.client2.**-dontwarn twitter4j.internal.logging.**-dontwarn com.dropbox.client2.**

Warning: twitter4j.internal.logging.Log4JLoggerFactory: can't find referenced class org.apache.log4j.LoggerWarning: twitter4j.internal.logging.SLF4JLoggerFactory: can't find referenced class org.slf4j.LoggerFactory...

Warning: twitter4j.internal.logging.Log4JLoggerFactory: can't find referenced class org.apache.log4j.LoggerWarning: twitter4j.internal.logging.SLF4JLoggerFactory: can't find referenced class org.slf4j.LoggerFactory...

Tip

Notes and warnings

Straight to the Troubleshooting page:

Warning: there were 12 unresolved references to classes or interfaces. You may need to add missing library jars or update their versions. If your code works fine without the missing classes, you can suppress the warnings with '-dontwarn' options. (http://proguard.sourceforge.net/manual/troubleshooting.html#unresolvedclass)

Warning: there were 12 unresolved references to classes or interfaces. You may need to add missing library jars or update their versions. If your code works fine without the missing classes, you can suppress the warnings with '-dontwarn' options. (http://proguard.sourceforge.net/manual/troubleshooting.html#unresolvedclass)

New

Shrinking

● Classes, fields, methods

Entry points

1) Activities, applications, services, fragments,...

→ provided automatically by Android build process

2) Introspection

→ must be specified in proguard-project.txt:

-keep public class * extends android.app.Activity-keep public class * extends android.app.Application-keep public class * extends android.app.Service…

-keep public class * extends android.app.Activity-keep public class * extends android.app.Application-keep public class * extends android.app.Service…

Optimization

At the bytecode instruction level:

● Dead code elimination

● Constant propagation

● Method inlining

● Class merging

● Remove logging code

● Peephole optimizations

● Devirtualization

● ...

Optimization exampleint answer = getAnswer(MyEnum.GREEN);int answer = getAnswer(MyEnum.GREEN);

int getAnswer(MyEnum e) { switch (e) { case RED: return 1; case GREEN: return 42; default: return 0; }}

int getAnswer(MyEnum e) { switch (e) { case RED: return 1; case GREEN: return 42; default: return 0; }}

enum MyEnum { RED, GREEN, BLUE}

enum MyEnum { RED, GREEN, BLUE}

New

Optimization exampleint answer = getAnswer(MyEnum.GREEN);int answer = getAnswer(MyEnum.GREEN);

int getAnswer(MyEnum e) { switch (e) { case RED: return 1; case GREEN: return 42; default: return 0; }}

int getAnswer(MyEnum e) { switch (e) { case RED: return 1; case GREEN: return 42; default: return 0; }}

enum MyEnum { RED, GREEN, BLUE}

enum MyEnum { RED, GREEN, BLUE}

int getAnswer(MyEnum e) { switch (Internal.$SwitchMap[e.ordinal()]) { case 1: return 1; case 2: return 42; default: return 0; }}

int getAnswer(MyEnum e) { switch (Internal.$SwitchMap[e.ordinal()]) { case 1: return 1; case 2: return 42; default: return 0; }}

class MyEnum { static final MyEnum RED = new MyEnum(“RED”, 0); static final MyEnum GREEN = new MyEnum(“GREEN”, 0); static final MyEnum BLUE = new MyEnum(“BLUE”, 0); static final MyEnum[] $VALUES = new MyEnum[] { RED, GREEN, BLUE }; ...}

class MyEnum { static final MyEnum RED = new MyEnum(“RED”, 0); static final MyEnum GREEN = new MyEnum(“GREEN”, 0); static final MyEnum BLUE = new MyEnum(“BLUE”, 0); static final MyEnum[] $VALUES = new MyEnum[] { RED, GREEN, BLUE }; ...}

New

Optimization exampleint answer = getAnswer(MyEnum.GREEN);int answer = getAnswer(MyEnum.GREEN);

int getAnswer(MyEnum e) { switch (e) { case RED: return 1; case GREEN: return 42; default: return 0; }}

int getAnswer(MyEnum e) { switch (e) { case RED: return 1; case GREEN: return 42; default: return 0; }}

enum MyEnum { RED, GREEN, BLUE}

enum MyEnum { RED, GREEN, BLUE}

int getAnswer(MyEnum e) { switch (Internal.$SwitchMap[e.ordinal()]) { case 1: return 1; case 2: return 42; default: return 0; }}

int getAnswer(MyEnum e) { switch (Internal.$SwitchMap[e.ordinal()]) { case 1: return 1; case 2: return 42; default: return 0; }}

class MyEnum { static final MyEnum RED = new MyEnum(“RED”, 0); static final MyEnum GREEN = new MyEnum(“GREEN”, 0); static final MyEnum BLUE = new MyEnum(“BLUE”, 0); static final MyEnum[] $VALUES = new MyEnum[] { RED, GREEN, BLUE }; ...}

class MyEnum { static final MyEnum RED = new MyEnum(“RED”, 0); static final MyEnum GREEN = new MyEnum(“GREEN”, 0); static final MyEnum BLUE = new MyEnum(“BLUE”, 0); static final MyEnum[] $VALUES = new MyEnum[] { RED, GREEN, BLUE }; ...}

New

class Internal { static final int[] $SwitchMap = new int[MyEnum.values().length];

static { $SwitchMap[MyEnum.RED.ordinal()] = 1; $SwitchMap[MyEnum.GREEN.ordinal()] = 2; }}

class Internal { static final int[] $SwitchMap = new int[MyEnum.values().length];

static { $SwitchMap[MyEnum.RED.ordinal()] = 1; $SwitchMap[MyEnum.GREEN.ordinal()] = 2; }}

Optimization exampleint answer = getAnswer(MyEnum.GREEN);int answer = getAnswer(MyEnum.GREEN);

int getAnswer(MyEnum e) { switch (e) { case RED: return 1; case GREEN: return 42; default: return 0; }}

int getAnswer(MyEnum e) { switch (e) { case RED: return 1; case GREEN: return 42; default: return 0; }}

enum MyEnum { RED, GREEN, BLUE}

enum MyEnum { RED, GREEN, BLUE}

int getAnswer(MyEnum e) { switch (Internal.$SwitchMap[e.ordinal()]) { case 1: return 1; case 2: return 42; default: return 0; }}

int getAnswer(MyEnum e) { switch (Internal.$SwitchMap[e.ordinal()]) { case 1: return 1; case 2: return 42; default: return 0; }}

class MyEnum { static final MyEnum RED = new MyEnum(“RED”, 0); static final MyEnum GREEN = new MyEnum(“GREEN”, 0); static final MyEnum BLUE = new MyEnum(“BLUE”, 0); static final MyEnum[] $VALUES = new MyEnum[] { RED, GREEN, BLUE }; ...}

class MyEnum { static final MyEnum RED = new MyEnum(“RED”, 0); static final MyEnum GREEN = new MyEnum(“GREEN”, 0); static final MyEnum BLUE = new MyEnum(“BLUE”, 0); static final MyEnum[] $VALUES = new MyEnum[] { RED, GREEN, BLUE }; ...}

New

class Internal { static final int[] $SwitchMap new int[MyEnum.values().length];

static { $SwitchMap[MyEnum.GREEN.ordinal()] = 1; $SwitchMap[MyEnum.RED.ordinal()] = 2; }}

class Internal { static final int[] $SwitchMap new int[MyEnum.values().length];

static { $SwitchMap[MyEnum.GREEN.ordinal()] = 1; $SwitchMap[MyEnum.RED.ordinal()] = 2; }}

int answer = getAnswer(2);int answer = getAnswer(2);

int getAnswer(int e) { switch (Internal.$SwitchMap[e]) { case 1: return 1; case 2: return 42; default: return 0; }}

int getAnswer(int e) { switch (Internal.$SwitchMap[e]) { case 1: return 1; case 2: return 42; default: return 0; }}

class Internal { static final int[] $SwitchMap = new int[3];

static { $SwitchMap[1] = 1; $SwitchMap[2] = 2; }}

class Internal { static final int[] $SwitchMap = new int[3];

static { $SwitchMap[1] = 1; $SwitchMap[2] = 2; }}

Optimization exampleint answer = getAnswer(MyEnum.GREEN);int answer = getAnswer(MyEnum.GREEN);

int getAnswer(MyEnum e) { switch (e) { case RED: return 1; case GREEN: return 42; default: return 0; }}

int getAnswer(MyEnum e) { switch (e) { case RED: return 1; case GREEN: return 42; default: return 0; }}

enum MyEnum { RED, GREEN, BLUE}

enum MyEnum { RED, GREEN, BLUE}

int getAnswer(MyEnum e) { switch (Internal.$SwitchMap[e.ordinal()]) { case 1: return 1; case 2: return 42; default: return 0; }}

int getAnswer(MyEnum e) { switch (Internal.$SwitchMap[e.ordinal()]) { case 1: return 1; case 2: return 42; default: return 0; }}

class MyEnum { static final MyEnum RED = new MyEnum(“RED”, 0); static final MyEnum GREEN = new MyEnum(“GREEN”, 0); static final MyEnum BLUE = new MyEnum(“BLUE”, 0); static final MyEnum[] $VALUES = new MyEnum[] { RED, GREEN, BLUE }; ...}

class MyEnum { static final MyEnum RED = new MyEnum(“RED”, 0); static final MyEnum GREEN = new MyEnum(“GREEN”, 0); static final MyEnum BLUE = new MyEnum(“BLUE”, 0); static final MyEnum[] $VALUES = new MyEnum[] { RED, GREEN, BLUE }; ...}

New

class Internal { static final int[] $SwitchMap new int[MyEnum.values().length];

static { $SwitchMap[MyEnum.GREEN.ordinal()] = 1; $SwitchMap[MyEnum.RED.ordinal()] = 2; }}

class Internal { static final int[] $SwitchMap new int[MyEnum.values().length];

static { $SwitchMap[MyEnum.GREEN.ordinal()] = 1; $SwitchMap[MyEnum.RED.ordinal()] = 2; }}

int answer = getAnswer(2);int answer = getAnswer(2);

int getAnswer(int e) { switch (Internal.$SwitchMap[e]) { case 1: return 1; case 2: return 42; default: return 0; }}

int getAnswer(int e) { switch (Internal.$SwitchMap[e]) { case 1: return 1; case 2: return 42; default: return 0; }}

class Internal { static final int[] $SwitchMap = new int[3];

static { $SwitchMap[1] = 1; $SwitchMap[2] = 2; }}

class Internal { static final int[] $SwitchMap = new int[3];

static { $SwitchMap[1] = 1; $SwitchMap[2] = 2; }}

int getAnswer(int e) { switch (e) { case 1: return 1; case 2: return 42; default: return 0; }}

int getAnswer(int e) { switch (e) { case 1: return 1; case 2: return 42; default: return 0; }}

Optimization exampleint answer = getAnswer(MyEnum.GREEN);int answer = getAnswer(MyEnum.GREEN);

int getAnswer(MyEnum e) { switch (e) { case RED: return 1; case GREEN: return 42; default: return 0; }}

int getAnswer(MyEnum e) { switch (e) { case RED: return 1; case GREEN: return 42; default: return 0; }}

enum MyEnum { RED, GREEN, BLUE}

enum MyEnum { RED, GREEN, BLUE}

int getAnswer(MyEnum e) { switch (Internal.$SwitchMap[e.ordinal()]) { case 1: return 1; case 2: return 42; default: return 0; }}

int getAnswer(MyEnum e) { switch (Internal.$SwitchMap[e.ordinal()]) { case 1: return 1; case 2: return 42; default: return 0; }}

class MyEnum { static final MyEnum RED = new MyEnum(“RED”, 0); static final MyEnum GREEN = new MyEnum(“GREEN”, 0); static final MyEnum BLUE = new MyEnum(“BLUE”, 0); static final MyEnum[] $VALUES = new MyEnum[] { RED, GREEN, BLUE }; ...}

class MyEnum { static final MyEnum RED = new MyEnum(“RED”, 0); static final MyEnum GREEN = new MyEnum(“GREEN”, 0); static final MyEnum BLUE = new MyEnum(“BLUE”, 0); static final MyEnum[] $VALUES = new MyEnum[] { RED, GREEN, BLUE }; ...}

New

class Internal { static final int[] $SwitchMap new int[MyEnum.values().length];

static { $SwitchMap[MyEnum.GREEN.ordinal()] = 1; $SwitchMap[MyEnum.RED.ordinal()] = 2; }}

class Internal { static final int[] $SwitchMap new int[MyEnum.values().length];

static { $SwitchMap[MyEnum.GREEN.ordinal()] = 1; $SwitchMap[MyEnum.RED.ordinal()] = 2; }}

int answer = getAnswer(2);int answer = getAnswer(2);

int getAnswer(int e) { switch (Internal.$SwitchMap[e]) { case 1: return 1; case 2: return 42; default: return 0; }}

int getAnswer(int e) { switch (Internal.$SwitchMap[e]) { case 1: return 1; case 2: return 42; default: return 0; }}

class Internal { static final int[] $SwitchMap = new int[3];

static { $SwitchMap[1] = 1; $SwitchMap[2] = 2; }}

class Internal { static final int[] $SwitchMap = new int[3];

static { $SwitchMap[1] = 1; $SwitchMap[2] = 2; }}

int getAnswer(int e) { switch (e) { case 1: return 1; case 2: return 42; default: return 0; }}

int getAnswer(int e) { switch (e) { case 1: return 1; case 2: return 42; default: return 0; }}

int answer = 42;int answer = 42;

How to enable optimization?

Ant and Eclipse: project.properties

# To enable ProGuard to shrink and obfuscate your code, uncomment thisproguard.config= ${sdk.dir}/tools/proguard/proguard-android-optimize.txt: proguard-project.txt

# To enable ProGuard to shrink and obfuscate your code, uncomment thisproguard.config= ${sdk.dir}/tools/proguard/proguard-android-optimize.txt: proguard-project.txt

Tip

How to enable optimization?

Gradle: build.gradle

android { buildTypes { release { runProguard true proguardFile getDefaultProguardFile('proguard-android-optimize.txt') } }

productFlavors { some_flavor { proguardFile 'proguard-project.txt' } }}

android { buildTypes { release { runProguard true proguardFile getDefaultProguardFile('proguard-android-optimize.txt') } }

productFlavors { some_flavor { proguardFile 'proguard-project.txt' } }}

New

Obfuscation

Traditional name obfuscation:

● Rename identifiers:class/field/method names

● Remove debug information: line numbers, local variable names,...

Obfuscation examplepublic class MyComputationClass { private MySettings settings; private MyAlgorithm algorithm; private int answer;

public int computeAnswer(int input) { … return answer; }}

public class MyComputationClass { private MySettings settings; private MyAlgorithm algorithm; private int answer;

public int computeAnswer(int input) { … return answer; }}

Obfuscation examplepublic class MyComputationClass { private MySettings settings; private MyAlgorithm algorithm; private int answer;

public int computeAnswer(int input) { … return answer; }}

public class MyComputationClass { private MySettings settings; private MyAlgorithm algorithm; private int answer;

public int computeAnswer(int input) { … return answer; }}

public class a { private b a; private c b; private int c;

public int a(int a) { … return c; }}

public class a { private b a; private c b; private int c;

public int a(int a) { … return c; }}

ProGuard documentation

developer.android.comdeveloper.android.com

proguard.sourceforge.netproguard.sourceforge.net

More application protection?

public class MyVerificationClass { public int checkSignatures() { … return activity .getPackageManager() .checkSignatures(“mypackage1”, “mypackage2”); }}

public class MyVerificationClass { public int checkSignatures() { … return activity .getPackageManager() .checkSignatures(“mypackage1”, “mypackage2”); }}

More application protection?

public class MyVerificationClass { public int checkSignatures() { … return activity .getPackageManager() .checkSignatures(“mypackage1”, “mypackage2”); }}

public class MyVerificationClass { public int checkSignatures() { … return activity .getPackageManager() .checkSignatures(“mypackage1”, “mypackage2”); }}

public class a { public int a() { … return a .getPackageManager() .checkSignatures(“mypackage1”, “mypackage2”); }}

public class a { public int a() { … return a .getPackageManager() .checkSignatures(“mypackage1”, “mypackage2”); }}

What to protect?

● Application

● Algorithms

● Communication

● Assets

● Keys

Code

Resources

Assets

Signatures

Attackers

Attackers

Time

Choice

Static analysis

● Disassemblers: dexdump, baksmali

● Decompilers: dex2jar + jad, JD-GUI, JEB,...

● Resources: aapt, apktool,...

Dynamic analysis

● Debuggers: adb,...

● Subverted runtime

● Cracking tools

Server-side code

Client-sideapplication

Server-sideapplication

?

String encryption

Be creative!

String KEY = “Secret key”;String KEY = “Secret key”;

String KEY = new String(Base64.decode(“U2VjcmV0IGtleQo=”));String KEY = new String(Base64.decode(“U2VjcmV0IGtleQo=”));

Reflection

java.lang.reflect

System.out.println(“Hello world!”);System.out.println(“Hello world!”);

Class clazz = Class.forName(“java.io.PrintStream”);

Method method = clazz.getMethod(“println”, new Class[] { String.class });

method.invoke(nul, new Object[] { “Hello world!” });

Class clazz = Class.forName(“java.io.PrintStream”);

Method method = clazz.getMethod(“println”, new Class[] { String.class });

method.invoke(nul, new Object[] { “Hello world!” });

Dynamic class loading

http://android-developers.blogspot.be/2011/07/custom-class-loading-in-dalvik.html

classes.dex

extra.dex

classes.dex

classes.dex

libutil.solibutil.so

Native code

Java Native Interface

libutil.so

classes.dex

Data encryption

● Standard cryptography APIs

● SQLCipher

Cipher cipher = Cipher.getInstance(“AES/CFB/NoPadding”);cipher.init(Cipher.ENCRYPT_MODE, key, initializationVector);

byte[] decrypted = cipher.doFinal(encrypted);

Cipher cipher = Cipher.getInstance(“AES/CFB/NoPadding”);cipher.init(Cipher.ENCRYPT_MODE, key, initializationVector);

byte[] decrypted = cipher.doFinal(encrypted);

White-box cryptography

Research: www.whiteboxcrypto.com

Real examples: DES, AES

final int KEY = 42;

int decryptValue(int encryptedValue) { return encryptedValue * KEY;}

final int KEY = 42;

int decryptValue(int encryptedValue) { return encryptedValue * KEY;}

int decryptValue(int encryptedValue) { encryptedValue += 5; encryptedValue *= 21; encryptedValue -= 105; encryptedValue += encryptedValue; return encryptedValue;}

int decryptValue(int encryptedValue) { encryptedValue += 5; encryptedValue *= 21; encryptedValue -= 105; encryptedValue += encryptedValue; return encryptedValue;}

Application checks

● Check application certificate:

● Check debug flag:

boolean debug = (activity.getApplicationInfo().flags & ApplicationInfo.FLAG_DEBUGGABLE) != 0;

boolean debug = (activity.getApplicationInfo().flags & ApplicationInfo.FLAG_DEBUGGABLE) != 0;

byte[] certificateData = activity .getPackageManager() .getPackageInfo(activity.getPackageName(), PackageManager.GET_SIGNATURES) .signatures[0] .toByteArray();

byte[] certificateData = activity .getPackageManager() .getPackageInfo(activity.getPackageName(), PackageManager.GET_SIGNATURES) .signatures[0] .toByteArray();

Environment checks

● Emulator detection

● Root detection

Conclusion

Nothing is unbreakable, but you can raise the bar:

● ProGuard

● String encryption

● Reflection

● Dynamic class loading

● Native code

● Data encryption

● Application checks

● Environment checks

● … DexGuard

DexGuard

● Specialized for Android

● Code and data

● Layers of protection

● Recommended techniques

● Low-level techniques

● Transparent

Tip

Code

Resources

Assets

Signatures

Saikoa website

www.saikoa.comwww.saikoa.com

Questions?

Open source

ShrinkingOptimizationObfuscation

Java bytecode

ProGuard

Saikoa

DexGuard

Dalvik bytecode

Protection