Need help with simplify?
Click the “chat” button below for chat support from the developer who created it, or find similar developers for support.

About the developer

Global Rank
#7,329
Topics of expertise
dalvik
deobfus...
malware...
deobfus...
malware...
email-n...
malware...
malware...
Location
Union City, CA
3.7K Stars 379 Forks Other 913 Commits 24 Opened issues

Description

Android virtual machine and deobfuscator

Services available

!
?

Need anything else?

Contributors list

# 7,329
Java
Android
dalvik
malware...
721 commits
# 20,956
Android
C
webasse...
deobfus...
25 commits
# 28,063
Lisp
malware...
deobfus...
c-sharp
7 commits
# 164,124
Java
deobfus...
Kotlin
Shell
4 commits
# 164,108
Java
deobfus...
Kotlin
Shell
4 commits
# 35,616
Android
Shell
Java
deobfus...
1 commit

Simplify

Build Status Coverage Status Coverity Scan Build Status

Generic Android Deobfuscator

Simplify virtually executes an app to understand its behavior and then tries to optimize the code so that it behaves identically but is easier for a human to understand. Each optimization type is simple and generic, so it doesn't matter what the specific type of obfuscation is used.

Before and After

The code on the left is a decompilation of an obfuscated app, and the code on the right has been deobfuscated.

Lots of method calls, no clear meaning Wow, such literal, much meaning

Overview

There are three parts to the project: smalivm, simplify, and the demo app.

  1. smalivm: Provides a virtual machine sandbox for executing Dalvik methods. After executing a method, it returns a graph containing all possible register and class values for every execution path. It works even if some values are unknown, such as file and network I/O. For example, any
    if
    or
    switch
    conditional with an unknown value results in both branches being taken.
  2. simplify: Analyzes the execution graphs from smalivm and applies optimizations such as constant propagation, dead code removal, unreflection, and some peephole optimizations. These are fairly simple, but when applied together repeatedly, they'll decrypt strings, remove reflection, and greatly simplify code. It does not rename methods and classes.
  3. demoapp: Contains simple, heavily commented examples for using smalivm in your own project. If you're building something that needs to execute Dalvik code, check it out.

Usage

usage: java -jar simplify.jar  [options]
deobfuscates a dalvik executable
 -et,--exclude-types    Exclude classes and methods which include REGEX, eg: "com/android", applied after include-types
 -h,--help                       Display this message
 -ie,--ignore-errors             Ignore errors while executing and optimizing methods. This may lead to unexpected behavior.
    --include-support            Attempt to execute and optimize classes in Android support library packages, default: false
 -it,--include-types    Limit execution to classes and methods which include REGEX, eg: ";->targetMethod\("
    --max-address-visits      Give up executing a method after visiting the same address N times, limits loops, default: 10000
    --max-call-depth          Do not call methods after reaching a call depth of N, limits recursion and long method chains, default: 50
    --max-execution-time      Give up executing a method after N seconds, default: 300
    --max-method-visits       Give up executing a method after executing N instructions in that method, default: 1000000
    --max-passes              Do not run optimizers on a method more than N times, default: 100
 -o,--output               Output simplified input to FILE
    --output-api-level    Set output DEX API compatibility to LEVEL, default: 15
 -q,--quiet                      Be quiet
    --remove-weak                Remove code even if there are weak side effects, default: true
 -v,--verbose             Set verbosity to LEVEL, default: 0

Building

Building requires the Java Development Kit 8 (JDK) to be installed.

Because this project contains submodules for Android frameworks, either clone with

--recursive
:
git clone --recursive https://github.com/CalebFenton/simplify.git

Or update submodules at any time with:

git submodule update --init --recursive

Then, to build a single jar which contains all dependencies:

./gradlew fatjar

The Simplify jar will be in

simplify/build/libs/
. You can test it's working by simplifying the provided obfuscated example app. Here's how you'd run it (you may need to change
simplify.jar
):
java -jar simplify/build/libs/simplify.jar -it "org/cf/obfuscated" -et "MainActivity" simplify/obfuscated-app.apk

To understand what's getting deobfuscated, check out Obfuscated App's README.

Troubleshooting

If Simplify fails, try these recommendations, in order:

  1. Only target a few methods or classes by using
    -it
    option.
  2. If failure is because of maximum visits exceeded, try using higher
    --max-address-visits
    ,
    --max-call-depth
    , and
    --max-method-visits
    .
  3. Try with
    -v
    or
    -v 2
    and report the issue with the logs and a hash of the DEX or APK.
  4. Try again, but do not break eye contact. Simplify can sense fear.

If building on Windows, and building fails with an error similar to:

Could not find tools.jar. Please check that C:\Program Files\Java\jre1.8.0_151 contains a valid JDK installation.

This means Gradle is unable to find a proper JDK path. Make sure the JDK is installed, set the

JAVA_HOME
environment variable to your JDK path, and make sure to close and re-open the command prompt you use to build.

Contributing

Don't be shy. I think virtual execution and deobfuscation are fascinating problems. Anyone who's interested is automatically cool and contributions are welcome, even if it's just to fix a typo. Feel free to ask questions in the issues and submit pull requests.

Reporting Issues

Please include a link to the APK or DEX and the full command you're using. This makes it much easier to reproduce (and thus fix) your issue.

If you can't share the sample, please include the file hash (SHA1, SHA256, etc).

Optimization Strategies

Constant Propagation

If an op places a value of a type which can be turned into a constant such as a string, number, or boolean, this optimization will replace that op with the constant. For example:

const-string v0, "VGVsbCBtZSBvZiB5b3VyIGhvbWV3b3JsZCwgVXN1bC4="
invoke-static {v0}, Lmy/string/Decryptor;->decrypt(Ljava/lang/String;)Ljava/lang/String;
# Decrypts to: "Tell me of your homeworld, Usul."
move-result v0

In this example, an encrypted string is decrypted and placed into

v0
. Since strings are "constantizable", the
move-result v0
can be replaced with a
const-string
:
const-string v0, "VGVsbCBtZSBvZiB5b3VyIGhvbWV3b3JsZCwgVXN1bC4="
invoke-static {v0}, Lmy/string/Decryptor;->decrypt(Ljava/lang/String;)Ljava/lang/String;
const-string v0, "Tell me of your homeworld, Usul."

Dead Code Removal

Code is dead if removing it cannot possibly alter the behavior of the app. The most obvious case is if the code is unreachable, e.g.

if (false) { // dead }
). If code is reachable, it may be considered dead if it doesn't affect any state outside of the method, i.e. it has no side effect. For example, code may not affect the return value for the method, alter any class variables, or perform any IO. This is a difficult to determine in static analysis. Luckily, smalivm doesn't have to be clever. It just stupidly executes everything it can and assumes there are side effects if it can't be sure. Consider the example from Constant Propagation:
const-string v0, "VGVsbCBtZSBvZiB5b3VyIGhvbWV3b3JsZCwgVXN1bC4="
invoke-static {v0}, Lmy/string/Decryptor;->decrypt(Ljava/lang/String;)Ljava/lang/String;
const-string v0, "Tell me of your homeworld, Usul."

In this code, the

invoke-static
no longer affects the return value of the method and let's assume it doesn't do anything weird like write bytes to the file system or a network socket so it has no side effects. It can simply be removed.
const-string v0, "VGVsbCBtZSBvZiB5b3VyIGhvbWV3b3JsZCwgVXN1bC4="
const-string v0, "Tell me of your homeworld, Usul."

Finally, the first

const-string
assigns a value to a register, but that value is never used, i.e. the assignment is dead. It can also be removed.
const-string v0, "Tell me of your homeworld, Usul."

Huzzah!

Unreflection

One major challenge with static analysis of Java is reflection. It's just not possible to know the arguments are for reflection methods without doing careful data flow analysis. There are smart, clever ways of doing this, but smalivm does it by just executing the code. When it finds a reflected method invocation such as:

invoke-virtual {v0, v1, v2}, Ljava/lang/reflect/Method;->invoke(Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;

It can know the values of

v0
,
v1
, and
v2
. If it's sure what the values are, it can replace the call to
Method.invoke()
with an actual non-reflected method invocation. The same applies for reflected field and class lookups.

Peephole

For everything that doesn't fit cleanly into a particular category, there's peephole optimizations. This includes removing useless

check-cast
ops, replacing
Ljava/lang/String;->
calls with
const-string
, and so on.

Deobfuscation Example

Before Optimization

.method public static test1()I
    .locals 2

new-instance v0, Ljava/lang/Integer;
const/4 v1, 0x1
invoke-direct {v0, v1}, Ljava/lang/Integer;-&gt;<init>(I)V

invoke-virtual {v0}, Ljava/lang/Integer;-&gt;intValue()I
move-result v0

return v0

.end method

All this does is

v0 = 1
.

After Constant Propagation

.method public static test1()I
    .locals 2

new-instance v0, Ljava/lang/Integer;
const/4 v1, 0x1
invoke-direct {v0, v1}, Ljava/lang/Integer;-&gt;<init>(I)V

invoke-virtual {v0}, Ljava/lang/Integer;-&gt;intValue()I
const/4 v0, 0x1

return v0

.end method

The

move-result v0
is replaced with
const/4 v0, 0x1
. This is because there is only one possible return value for
intValue()I
and the return type can be made a constant. The arguments
v0
and
v1
are unambiguous and do not change. That is to say, there's a consensus of values for every possible execution path at
intValue()I
. Other types of values that can be turned into constants:
  • numbers -
    const/4
    ,
    const/16
    , etc.
  • strings -
    const-string
  • classes -
    const-class

After Dead Code Removal

.method public static test1()I
    .locals 2

const/4 v0, 0x1

return v0

.end method

Because the code above

const/4 v0, 0x1
does not affect state outside of the method (no side-effects), it can be removed without changing behavior. If there was a method call that wrote something to the file system or network, it couldn't be removed because it affects state outside the method. Or if
test()I
took a mutable argument, such as a
LinkedList
, any instructions that accessed it couldn't be considered dead.

Other examples of dead code:

  • unreferenced assignments - assigning registers and not using them
  • unreached / unreachable instructions -
    if (false) { dead_code(); }

License

This tool is available under a dual license: a commercial one suitable for closed source projects and a GPL license that can be used in open source software.

Depending on your needs, you must choose one of them and follow its policies. A detail of the policies and agreements for each license type are available in the LICENSE.COMMERCIAL and LICENSE.GPL files.

Further Reading

We use cookies. If you continue to browse the site, you agree to the use of cookies. For more information on our use of cookies please see our Privacy Policy.