.NET & Java Reversing

// dnSpy - .NET decompiler and debugger
// Open .exe or .dll → Browse classes → View decompiled C#

// Example decompiled output
public class LicenseChecker {
    public static bool ValidateLicense(string key) {
        string expected = GenerateKey(Environment.MachineName);
        return key == expected;
    }
    
    private static string GenerateKey(string seed) {
        using (MD5 md5 = MD5.Create()) {
            byte[] hash = md5.ComputeHash(Encoding.UTF8.GetBytes(seed));
            return BitConverter.ToString(hash).Replace("-", "");
        }
    }
}

// Patching with dnSpy:
// 1. Right-click method → Edit Method
// 2. Change: return key == expected;
//    To:     return true;
// 3. File → Save Module

// Alternative tools:
// - ILSpy (view only)
// - dotPeek (JetBrains)
// - de4dot (deobfuscation)

# Java decompilation tools
# JD-GUI - Simple GUI decompiler
# Procyon - Modern decompiler
# CFR - Handles modern Java well
# JADX - Good for Android APKs

# Decompile JAR with CFR
java -jar cfr.jar target.jar --outputdir ./decompiled

# Decompile single class
java -jar cfr.jar MyClass.class

# Android APK analysis
jadx -d output/ app.apk

# Common obfuscators:
# - ProGuard (free, basic)
# - DexGuard (commercial)
# - Allatori (Java)

# De-obfuscation strategies:
# - Rename classes/methods based on usage
# - String decryption (find decrypt method, hook it)
# - Control flow analysis