Concrete examples, recommended workflow, and short code snippets showing how the Vigorous control-flow algorithm in Skater .NET Obfuscator is typically applied. Where appropriate, this guide cites official Skater documentation and release notes.

The Vigorous algorithm is a control-flow obfuscation mode that performs deep rewriting of method bodies and control-flow graphs: reorders branches and basic blocks, splits/merges blocks, inserts dummy branches and state machines, and generally transforms clean IL into semantically equivalent but hard-to-follow code. This is intended to significantly raise the effort required for decompilation and human analysis.

Open your assembly in Skater → go to the Control Flow tab → choose the Vigorous algorithm for selected methods or modules. Save settings to an XML profile if you want repeatable runs.

Skater supports command-line options; common switches include flags to enable control flow for all methods or to provide an XML settings file exported from GUI.

REM Example: run Skater with settings file
Skater.exe -s:"C:\SkaterProfiles\MyVigorousProfile.xml" -in:"bin\Release\MyApp.dll" -out:"bin\Release\Obf\" -writeLog

(You can export the XML profile from the GUI, then reuse it in automated builds).

Instead of “all methods”, pick a handful of sensitive methods (license checks, cryptographic routines, business logic entry points). This reduces risk of breaking reflection/interop and keeps runtime overhead manageable.

Vigorous operates at the IL level; the decompiled C# output after Vigorous will usually be messy. The examples below show typical patterns you will see after Vigorous transformation (conceptual, actual output depends on many factors).

public int MultiplyIfPositive(int x, int y)
{
    if (x > 0)
        return x * y;
    return 0;
}

public int MultiplyIfPositive(int x, int y)
{
    int result = 0;
    int state = 1;
    while (true)
    {
        switch (state)
        {
            case 1:
                if (x <= 0) { state = 10; continue; }
                state = 2; continue;
            case 2:
                result = x * y ^ 0x0;   // dummy arithmetic inserted
                state = 99; continue;
            case 10:
                result = 0; state = 99; continue;
            case 99:
                return result;
        }
    }
}

Notes: dummy locals/ops, explicit state machine, unnatural branching and jumps are common artifacts. Real Vigorous output is often more complex (split blocks, extra exception handlers, flattened loops).

/* before */
public bool IsAdult(int age)
{
    return age >= 18;
}

/* conceptual Vigorous-style after */
public bool IsAdult(int a)
{
bool r = false;
int pc = 0;
for (;;)
{
switch (pc)
{
case 0:
if (a < 18) { pc = 5; continue; }
r = true; pc = 9; continue;
case 5:
r = false; pc = 9; continue;
case 9:
return r;
}
}
} 

1. Start small: apply Vigorous to one assembly and to a very limited set of methods (license check, algorithm core). Run tests.
2. Full test cycle: unit tests, integration tests, reflection/serialization checks, P/Invoke / interop scenarios, exception-path tests and performance benchmarks. Vigorous rewrites exception handling and IL shapes, so tests often find issues.
3. Keep clean fallback builds: keep un-obfuscated or lightly-obfuscated artifacts for debugging and rollback.
4. Document settings: save the Skater XML profile and record Skater version & profile used for each release (helps reproduce/diagnose). Release notes mention Vigorous improvements in recent updates, keep Skater updated.
5. Combine protections carefully: string encryption, renaming and control flow can be layered, but layering increases risk; validate after each added protection.

You can export a profile from the GUI. The snippet below shows the important ideas: selecting Vigorous control flow and listing methods you want to protect. (Actual tag names depend on the exact Skater XML schema, export from GUI to produce correct XML.)

<SkaterProject>
  <InputFile>bin\Release\MyApp.dll</InputFile>
  <OutputDirectory>bin\Release\Obf</OutputDirectory>

  <ControlFlow algorithm="Vigorous">
    <Enable>true</Enable>
    <Methods>
      <Method name="MyApp.Security.LicenseChecker.VerifyLicense"/> 
      <Method name="MyApp.Algo.CryptoEngine.Encrypt"/> 
    </Methods>
  </ControlFlow>

  <StringEncryption>true</StringEncryption>
  <RenameSymbols>true</RenameSymbols>
</SkaterProject>

• All unit tests passed on the obfuscated assembly
• Integration tests (including reflection & serialization) passed
• Manual smoke tests for UI, plugins and native interop
• Performance benchmarks acceptable (Vigorous can add runtime overhead)
• Logging/telemetry still useful for debugging field issues