# Netwide Assembler

## Download and Install

The NASM assembler will be used to compile our shellcode. The version I am using is 2.16.01 and can be downloaded from <https://www.nasm.us/pub/nasm/releasebuilds/2.16.01/win64/>.

Download the 64-bit installer and run it.

Once the installer has completed make sure that the path for NASM has been added to the system path variable:

<div align="left"><figure><img src="/files/Dt6sMf54OzgvlaT9aTwU" alt="" width="563"><figcaption><p>System Path variable</p></figcaption></figure></div>

## Batch File

Now is a good time to show how I compile my assembly. I have created two Windows batch files. One to compile in to an executable, and one to compile to a raw binary file.

We can use the executable to debug shellcode in Windbg Preview. The batch file is shown below:

{% code title="compile.bat" lineNumbers="true" %}

```batch
del shellcode.obj
del shellcode.exe
nasm -f win64 shellcode.asm -o shellcode.obj
link /ENTRY:main /MACHINE:X64 /NODEFAULTLIB /SUBSYSTEM:CONSOLE shellcode.obj
```

{% endcode %}

The second batch file is used to compile shellcode into a raw `.bin` file. This is useful for writing shellcode that can be put in C exploit code:

{% code title="hex-encode.bat" lineNumbers="true" %}

```batch
nasm -f bin -o shellcode.bin shellcode.asm
Hex2.exe .\shellcode.bin
```

{% endcode %}

The sharp-eyed will notice that the batch file also runs an executable called `Hex2.exe`.

## Hex2

Like all other tools and workflows this is completely optional. There are plenty of hex viewers out there but I wrote my own in C#:

{% code title="Hex2.cs" lineNumbers="true" %}

```csharp
static void Main(string[] args)
{
    byte[] file = System.IO.File.ReadAllBytes(args[0]);

    StringBuilder sb = new StringBuilder();
    sb.Append("const unsigned char shellcode[] = {");

    string hex = BitConverter.ToString(file).Replace("-", ", 0x");
    hex = "0x" + hex;

    sb.Append(hex);
    sb.Append("};");

    Console.WriteLine(sb.ToString());
 }
```

{% endcode %}

This makes my shellcode workflow for writing exploits in C quick and clean.

The image below shows the output, which can easily be copied and pasted into C code:

<figure><img src="/files/2JTv3WRR1mqzvmfBAd8g" alt=""><figcaption><p>Hex2 formatting for C</p></figcaption></figure>


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