Skater .NET Obfuscator

Rustemsoft LLC proposes Skater .NET Obfuscator, an obfuscation tool for .NET code protection. It implements all known software protection techniques and obfuscation algorithms.
If you would like periodically obfuscate your .NET products the Skater .NET Obfuscator is for you. Rustemsoft LLC is using the Skater for internal needs securing all Rustemsoft LLC .NET executables and assemblies. Its command-line version running in batch mode is much useful for your scheduled products updates. You have to assign settings for an assembly in GUI version first. Then the batch obfuscate task will use the settings.

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Main features of Skater .NET Obfuscator

Prohibits reverse engineering
Obfuscated application usually is not recompilable
Processes any .NET application, executable or assembly
Encrypts string constants
Compatible with any .NET framework from 1.0 through 4.5
Control flow obfuscation stops decompilers and deobfuscators
Scrambles class names, method names, field names etc.
Protects XAML (baml) files in WPF application
It works well on both (x86 and x64) platforms

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Read .NET obfuscator documentation

Application vulnerabilities, Intellectual Property theft and revenue loss are among the most serious risks facing companies today. According to Business Software Alliance statistics, four out of every ten software programs is pirated in software business, world wide.

Unauthorized access to source code can offer a quick back entrance into your systems, business processes and revenue streams. Global piracy rate has increased 40% over the past years and nearly $11 billion is lost. This is definitely a clear threat for software producers and thus to global economy. With more than half of million developers with some level of access to .NET reengineering tools providing near instant access to source from any .NET binary, organizations across industries are entrusting on obfuscation to managing these risks. Over the years, several software protection techniques have been developed, code obfuscation is one of them and it is very promising.

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Code obfuscation is a form of software protection against unauthorized reverse-engineering.
The chief functions of any software protection technique can be determined as detection of pirate attempts to decipher or tamper software, protection against such attempts and alteration of software to ensure that it functionality degrades in an undetectable manner if the protection fails.

Cardinal obfuscation techniques:

Private and Public members names obfuscation.
It scrambles names of classes, methods, variables, and other assembly members. It makes assembly code reverse engineering much harder by obfuscating names. Some Skater settings allow to generated names that will prevent recompilation.
Public members in dll libraries are advisedly reserved from obfuscation because they are intended to be used in external assembly code. If you are sure some of public members are not to be accessed from outside, you may want to obfuscate them.
For exe executables you may consider the assemblies to be self-contained, and set obfuscation of all possible names very aggressively, including Public Members.

String encryption.
The string encryption function allows you to select literal values of string data type to be encrypted. You may select all strings to be encrypted. Also you may mark some specific strings to obfuscate. You have choice to apply a cryptography method for the string encryption. Only specified strings will be encrypted /obfuscated.
Since Strings can provide useful clues for anyone trying to reverse-engineer your code it makes sense to protect your string data from spying eyes. It will not prevent an absolute hacker from deciphering the conversion and seeing your data. However, for example, an attacker trying to break a licensing routine would first focus attention on Strings having to do with licensing to locate the appropriate spot of code. Skater can make this more difficult by encrypting the strings in your .NET assembly. This is done by inserting a decryption routine into the assembly and calling the decryption code at runtime to return the original Strings.

Control Flow obfuscation intended to stop decompilers and deobfuscators from functioning correctly.
Control Flow obfuscation subdues reverse engineering by scrambling .NET methods (functions and procedures) code. The Control Flow obfuscation algorithm distorts and reorders the IL code in the assembly, inserting bait branch instructions while preserving code semantics. This obfuscating essentially converts assembly method implementations into "spaghetti code", making interpretation by human hackers and decompiler tools much more difficult.
Actually Control Flow obfuscation involves the insertion of additional instructions. Applying of this feature increases the size of the output assembly. If a maximum level of code protection is not required for your assembly, you may want to consider disabling this feature to minimize your output executable code size.
Control Flow obfuscation discourages reverse engineering and malicious tampering of software codes by applying false conditional statements and other misleading constructs in order to confuse and break decompilers. Given the original source codes and desired obfuscation criteria, the proposed Control Flow obfuscation works by decomposing the source codes into fragments and then applying various transforms to the code fragments. As the Skater?s output, the transformed fragments are re-assembled and obfuscated with the designated obfuscation criteria. Moreover, since only Control Flows are obfuscated with a sequence of transformations that produce equivalent results of the original fragments, the final output can still preserve the same execution results as the original codes.

Example

Let's try to write a simple command-line application and then obfuscate it. The following console programs are the VB.NET and C# version of the "Hello World!" program, which displays the string "Hello World!" Actually it is not the traditional "Hello World!" and it displays in addition today's date and current time. We have added couple of private variables to see what happen when we obfuscate them.

VB .NET

Imports System
Module Module1
Private str As String = "Hello World! Today is:"
Private today As Date = Now
Sub Main()
Console.WriteLine(str + CStr(today))
End Sub
End Module

C#

using System;
struct Module1
{
private string str = "Hello World! Today is:";
private System.DateTime today = Now;
void Main()
{
Console.WriteLine(str + System.Convert.ToString(today));
}
}

You can see four highlighted members' names. Two are private variables' names today and str. Module1 is name of the class. Main is name of method that is single method in the simple class.
Now we are ready to compile the simple code in .NET environment. We may get ConsoleApplication1.exe executable file as a result of compilation. What is inside in the executable? Why do people say we need to hide our .NET stuff?
The .NET Framework SDK ships with a disassembler utility called ILDasm that allows you to decompile .NET assemblies into IL (Intermediate Language) Assembly Language statements. To decompile the ConsoleApplication1.exe file start ILDasm on the command line. Take a look what we got after the decompilation:

IL

.class private auto ansi sealed beforefieldinit Module1
extends [mscorlib]System.Object
{
.custom instance void [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.
StandardModuleAttribute::.ctor() = ( 01 00 00 00 )
.field private static string str
.field private static valuetype [mscorlib]System.DateTime today
.method private specialname rtspecialname static
void .cctor() cil managed
{
.maxstack 8
IL_0000: ldstr "Hello World! Today is:"
IL_0005: stsfld string ConsoleApplication1.Module1::str
IL_000a: call valuetype [mscorlib]System.DateTime [Microsoft.VisualBasic]Microsoft.
VisualBasic.DateAndTime::get_Now()
IL_000f: stsfld valuetype [mscorlib]System.DateTime ConsoleApplication1.Module1::today
IL_0014: nop
IL_0015: ret
} // end of method Module1::.cctor
.method public static void Main() cil managed
{
.entrypoint
.custom instance void [mscorlib]System.STAThreadAttribute::.ctor() = ( 01 00 00 00 )
.maxstack 8
IL_0000: nop
IL_0001: ldsfld string ConsoleApplication1.Module1::str
IL_0006: ldsfld valuetype [mscorlib]System.DateTime ConsoleApplication1.Module1::today
IL_000b: call string [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.StringType::
FromDate(valuetype [mscorlib]System.DateTime)
IL_0010: call string [mscorlib]System.String::Concat(string,
string)
IL_0015: call void [mscorlib]System.Console::WriteLine(string)
IL_001a: nop
IL_001b: nop
IL_001c: ret
} // end of method Module1::Main
} // end of class Module1

Everything looks pretty obvious and understandable in the IL script. Is not it? Right, it is hard to figure out the IL code for us more mortals. So if you are now guessing your .NET source code will be accessible only to a small circle of technical folks who actually know IL Assembly Language, think again. You can take this step further and actually recreate the source code by using some much sophisticated decompilers. These decompilation tools can decompile a .NET assembly directly back to a high level language like C#, VB .NET, or C++.
Ok, we are ready to obfuscate the sample ConsoleApplication1.exe executable by using Skater .NET Obfuscator. Open the exe file in Skater Obfuscator. In the Obfuscator interface go to Options tab and select 'Alpha-Numeric characters' under 'Naming Conventions'. Choose all Private and all Public members obfuscation mode.
When you run the obfuscated ConsoleApplication1.exe it produces the same result. Take a look what changed inside the simple program. We need to run the ILDasm.exe again against the new obfuscated executable and it will give us the following IL script:

IL

.class private auto ansi sealed beforefieldinit '0AAAA'
extends [mscorlib]System.Object
{
.custom instance void [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.
StandardModuleAttribute::.ctor() = ( 01 00 00 00 )
.field private static string '1AAA0'
.field private static valuetype [mscorlib]System.DateTime '2AAAA'
.method private specialname rtspecialname static
void .cctor() cil managed
{
.maxstack 8
IL_0000: ldstr "Hello World! Today is:"
IL_0005: stsfld string ConsoleApplication1.'0AAAA'::'1AAA0'
IL_000a: call valuetype [mscorlib]System.DateTime [Microsoft.VisualBasic]Microsoft.
VisualBasic.DateAndTime::get_Now()
IL_000f: stsfld valuetype [mscorlib]System.DateTime ConsoleApplication1.'0AAAA'::'2AAAA'
IL_0014: nop
IL_0015: ret
} // end of method '0AAAA'::.cctor
.method public static void '1AAAA'() cil managed
{
.entrypoint
.custom instance void [mscorlib]System.STAThreadAttribute::.ctor() = ( 01 00 00 00 )
.maxstack 8
IL_0000: nop
IL_0001: ldsfld string ConsoleApplication1.'0AAAA'::'1AAA0'
IL_0006: ldsfld valuetype [mscorlib]System.DateTime ConsoleApplication1.'0AAAA'::'2AAAA'
IL_000b: call string [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.StringType::
FromDate(valuetype [mscorlib]System.DateTime)
IL_0010: call string [mscorlib]System.String::Concat(string,
string)
IL_0015: call void [mscorlib]System.Console::WriteLine(string)
IL_001a: nop
IL_001b: nop
IL_001c: ret
} // end of method '0AAAA'::'1AAAA'
} // end of class '0AAAA'

Skater .NET Obfuscator just replaced member names with alpha-numeric combinations that makes harder to understand the code. However it is not so big trick and every Obfuscator can do that. Everyone can replace the alpha-numeric char combinations with some eye-friendly names. Moreover, by using ILasm.exe (one more .NET Framework SDK assembler utility that allows you to compile IL code back into an executable) we can easily recompile the obfuscated IL output and it will work without problems.
Skater .NET Obfuscator can generate a non-recompilable executables. See the IL script below.

IL

.class private auto ansi sealed beforefieldinit '?'
extends [mscorlib]System.Object
{
.custom instance void [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.
StandardModuleAttribute::.ctor() = ( 01 00 00 00 )
.field private static string '?'
.field private static valuetype [mscorlib]System.DateTime '?'
.method private specialname rtspecialname static
void .cctor() cil managed
{
.maxstack 8
IL_0000: ldstr "Hello World! Today is:"
IL_0005: stsfld string ConsoleApplication1.'?'::'?'
IL_000a: call valuetype [mscorlib]System.DateTime [Microsoft.VisualBasic]Microsoft.
VisualBasic.DateAndTime::get_Now()
IL_000f: stsfld valuetype [mscorlib]System.DateTime ConsoleApplication1.'?'::'?'
IL_0014: nop
IL_0015: ret
} // end of method '?'::.cctor
.method public static void '?'() cil managed
{
.entrypoint
.custom instance void [mscorlib]System.STAThreadAttribute::.ctor() = ( 01 00 00 00 )
.maxstack 8
IL_0000: nop
IL_0001: ldsfld string ConsoleApplication1.'?'::'?'
IL_0006: ldsfld valuetype [mscorlib]System.DateTime ConsoleApplication1.'?'::'?'
IL_000b: call string [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.StringType::
FromDate(valuetype [mscorlib]System.DateTime)
IL_0010: call string [mscorlib]System.String::Concat(string,
string)
IL_0015: call void [mscorlib]System.Console::WriteLine(string)
IL_001a: nop
IL_001b: nop
IL_001c: ret
} // end of method '?'::'?'
} // end of class '?'

Sure, the presented above IL code can not be compiled or the compiled executable will not work well. As you can see all member names has the same single '?' character representation. We can get the result by using Skater .NET Obfuscator special settings. In the Obfuscator interface go to Options tab and select '?' characters under 'Naming Conventions'.
The member names obfuscation is the very first essential step of .NET assembly obfuscation. You need to apply other Skater .NET Obfuscator methods and algorithms to better secure your .NET apps.

You need the Skater .NET Obfuscator for the following reasons:

1. You have a clear understanding of obfuscation benefits and appropriate use cases.
2. You generally understand that obfuscation prevents source code extraction.
3. You have practical understanding of how and when obfuscation should be used.
4. Also your organization has a consistent approach to assessing the risk of source code extraction.


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