Secret Agent Vibes: Encode and Decode Files with the Windows Command Line

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Have you ever wanted to hide a message in plain sight? Or maybe just look super cool using the command line like a digital ninja? 😎 In this post, I’ll show you how to encode and decode files using the Windows command line — no extra software required!

We’re not doing anything fancy like encryption here — we’re just encoding data using a format called Base64. It’s a neat way to turn your files into a scrambled-looking format that’s still perfectly reversible.

Let’s jump right in!

Step 1: Create a File to Encode

First, let’s make a little text file that contains a top secret message.

Open a Command Prompt window and type the following:

CMD
echo This is a secret message! > secret.txt

That creates a file called secret.txt in your current folder, containing the sentence:

CMD
This is a secret message!

You can peek inside it just to be sure:

CMD
type secret.txt

You should see your message printed back at you.

Step 2: Encode It Using certutil

Here’s where the magic happens.

Windows has a built-in utility called certutil that, among many other things, can encode files in Base64 format. Try this:

CMD
certutil -encode secret.txt secret_encoded.txt

Output:
Input Length = 28
Output Length = 98
CertUtil: -encode command completed successfully.

That command tells Windows to take the file secret.txt, encode it using Base64, and save the result as secret_encoded.txt.

Open secret_encoded.txt in Notepad or use type to look at it:

CMD
type secret_encoded.txt

Output:
-----BEGIN CERTIFICATE-----
VGhpcyBpcyBhIHNlY3JldCBtZXNzYWdlISANCg==
-----END CERTIFICATE-----

Congratulations — you’ve just encoded your first file like a secret agent 🕶️

Step 3: Decode It Back to the Original

Now let’s bring it back from its encoded form.

Use this command:

CMD
certutil -decode secret_encoded.txt secret_decoded.txt

Output:
Input Length = 98
Output Length = 28
CertUtil: -decode command completed successfully.

This tells Windows to take the Base64-encoded file and turn it back into plain text.

To confirm it worked:

CMD
type secret_decoded.txt

Output:
This is a secret message!

Bonus: Compare Files

Let’s compare the original and decoded files to be sure they’re identical.

Use the fc command:

CMD
fc secret.txt secret_decoded.txt

Output:
Comparing files secret.txt and SECRET_DECODED.TXT
FC: no differences encountered

If you get the message no differences encountered, then everything worked perfectly.

⚠️ Quick Notes Before You Get Carried Away

  • Encoding is not encryption: Don’t use this to protect sensitive data. Base64 is easily reversible.
  • You can use this trick with text files, scripts, even small binary files — but be aware that the encoded version will be bigger in size.
  • Wanna get fancier? PowerShell and tools like openssl offer even more control, but we’ll save that for another post.

Wrap-Up

That’s it — now you know how to use the Windows command line to encode and decode files like a pro. It’s a simple trick, but super useful for learning and a great stepping stone toward understanding data transformation and security basics.

Got any cool uses for this? Or want to see the PowerShell version next? Let me know in the comments!

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