> For the complete documentation index, see [llms.txt](https://sarpers-organization.gitbook.io/ctftricks/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://sarpers-organization.gitbook.io/ctftricks/_chapter-intro-16/.net/code-analysis/trick-0425.md).

# Reverse Engineer .NET Executable (Dnspy)

***

Use a .NET decompiler like dnSpy or ILSpy to analyze the compiled executable. Open the target file and navigate through namespaces, classes, and methods, examining the code for logic related to data processing, string handling, or potentially obfuscated data within arrays or loops. For example, a challenge might involve identifying a function that iterates through an array of values, applying a simple decryption algorithm like a XOR operation with a constant key to reveal hidden data or a flag. The XOR encryption algorithm is a simple algorithm that uses the XOR logical operator to encrypt data. It is a symmetric encryption algorithm, meaning that the same key is used for both encryption and decryption. A common implementation pattern in C# might involve iterating through the input data and XORing each element with a character or byte from a key, often cycling through the key if it's shorter than the data:

```csharp
using System;
using System.Text;

public class XorExample
{
    public static string XorEncryptDecrypt(string text, string key)
    {
        StringBuilder result = new StringBuilder();

        for (int i = 0; i < text.Length; i++)
        {
            result.Append((char)(text[i] ^ key[i % key.Length]));
        }

        return result.ToString();
    }
}
```

This same logic can be found implemented in other languages. For instance, a Python implementation of the core XOR cipher logic would look like this:

```python
def xor_cipher(message, key):
    encrypted_message = ""
    key_length = len(key)
    for i in range(len(message)):
        encrypted_char = chr(ord(message[i]) ^ ord(key[i % key_length]))
        encrypted_message += encrypted_char
    return encrypted_message
```

By identifying such patterns in the decompiled code, you can understand how the hidden data is processed and potentially replicate the decryption logic to recover the original information.