Bandit Level 10 to 11: The Secret Language of Base64

Introduction

So far, we’ve located files, filtered their contents, and even extracted text from binary data. Bandit Level 10 to 11 introduces a new core concept: data encoding. The password is in plain sight, but it’s been transformed into a different format.

This level teaches us how to recognize and reverse Base64 encoding, a common method for representing binary data as text. 🧑‍💻

The Challenge: Level 10 Goal

The objective for this level is straightforward:

The password for the next level is stored in the file data.txt, which contains base64 encoded data.

Our mission is to decode this data to reveal the original password.

Step-by-Step Walkthrough

Let’s translate this encoded message.

Step 1: Log into bandit10

Use the password you extracted from the binary file in the last level to SSH into bandit10.

ssh [email protected] -p 2220

Step 2: Inspect the Data

First, take a look at the contents of data.txt.

cat data.txt

You will see a long, continuous string of letters, numbers, and perhaps a + or / sign, ending with an = sign. This is a classic signature of Base64 encoding.

VGhlIHBhc3N3b3JkIGlzIElGcjlCbzJDV0luV3p6N0dJU1JzT0VobEpERXNqcE5NCg==

Step 3: The Solution - The base64 Command

Linux provides a dedicated utility for this task: the base64 command. By default, it encodes data. To decode, we use the -d (or --decode) flag.

We can tell the command to decode the file directly.

Step 4: Execute the Decode Command

Run the base64 command with the -d flag on our data.txt file.

base64 -d data.txt

The command will process the encoded string and print the original, human-readable text to the terminal, which is our password.

# Example Output
The password is IF...

Alternative Method (Piping):

You can also achieve the same result by piping the output of cat into the base64 command.

cat data.txt | base64 -d

This is a common pattern when you’re working with streams of data rather than just files.

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Key Concepts Learned

1. Base64 Encoding: We learned that Base64 is an encoding scheme, not an encryption one. It is used to safely transmit binary data through text-only channels (like email or HTML). It is easily reversible by anyone.
2. The base64 Command: This is the key tool. We learned how to use it and its most important flag, -d, for decoding.
3. Recognizing Encoded Data: You’re now more familiar with what Base64-encoded text looks like, which is a valuable skill for identifying data types during a CTF or penetration test.

Conclusion

You’ve successfully decoded your first piece of Base64 data! This is a fundamental skill, as encoding is used everywhere in computing.

Save the password for bandit11 and let’s keep the momentum going!