> ## Documentation Index
> Fetch the complete documentation index at: https://writeups.dudji.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Natas 8

> Natas Level 8 — reversing a multi-step encoding chain to recover the secret.

## Overview

| Field    | Value                                      |
| -------- | ------------------------------------------ |
| URL      | `http://natas8.natas.labs.overthewire.org` |
| Username | `natas8`                                   |
| Password | `xcoXLmzMkoIP9D7hlgPlh9XD7OgLAe5Q`         |

Another *"Input secret"* form. The *"View sourcecode"* link reveals the PHP — including the encoded secret and the function used to encode it.

***

## Hints

<AccordionGroup>
  <Accordion title="Hint 1 — Read the encoding function">
    The source shows `$encodedSecret` (the target value) and the `encodeSecret()` function that transforms input before comparison. Read the function carefully — what three operations does it apply, and in what order?

    ```php theme={"theme":{"light":"github-light","dark":"tokyo-night"}}
    function encodeSecret($secret) {
        return bin2hex(strrev(base64_encode($secret)));
    }
    ```
  </Accordion>

  <Accordion title="Hint 2 — Reverse the chain">
    The encoding order is: `base64_encode` → `strrev` → `bin2hex`. To recover the original secret, apply the inverse operations in reverse order:

    1. Hex decode the stored value
    2. Reverse the resulting string
    3. Base64 decode

    A tool like [CyberChef](https://gchq.github.io/CyberChef/) lets you chain these operations visually.
  </Accordion>
</AccordionGroup>

***

## Solution

<Accordion title="Full walkthrough">
  <Steps>
    <Step title="Start with the encoded secret">
      ```
      3d3d516343746d4d6d6c315669563362
      ```
    </Step>

    <Step title="Step 1 — Hex decode">
      Decode the hex string:

      ```
      ==QcCtmMml1ViV3b
      ```

      The `==` at the start is a giveaway that this is a reversed Base64 string (padding normally appears at the end).
    </Step>

    <Step title="Step 2 — Reverse the string">
      Reverse `==QcCtmMml1ViV3b`:

      ```
      b3ViV1lmMmtCcQ==
      ```
    </Step>

    <Step title="Step 3 — Base64 decode">
      Decode `b3ViV1lmMmtCcQ==`:

      ```
      oubWYf2kBq
      ```

      This is the secret.
    </Step>

    <Step title="Submit">
      Enter `oubWYf2kBq` in the form and submit.
    </Step>
  </Steps>
</Accordion>

## With curl

```bash theme={"theme":{"light":"github-light","dark":"tokyo-night"}}
# POST the decoded secret directly to the form
curl -s -u natas8:xcoXLmzMkoIP9D7hlgPlh9XD7OgLAe5Q \
  -X POST -d "secret=oubWYf2kBq&submit=1" \
  http://natas8.natas.labs.overthewire.org/ \
  | grep -i password
```

## Password

```
natas9: ZE1ck82lmdGIoErlhQgWND6j2Wzz6b6t
```