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<!DOCTYPE html>
<html lang="en">
<head>
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    <title>Hiding in Plain Sight - Instruo CTF 2025</title>
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                    <h1 class="text-4xl font-bold text-white">Hiding in Plain Sight</h1>
                </div>
                <div class="flex flex-wrap gap-3">
                    <span class="inline-flex items-center px-3 py-1 rounded-full text-sm font-medium bg-gray-700 text-white">Steganography</span>
                    <span class="inline-flex items-center px-3 py-1 rounded-full text-sm font-medium bg-blue-700 text-white">150 pts</span>
                    <span class="inline-flex items-center px-3 py-1 rounded-full text-sm font-medium bg-green-600 text-white">Easy</span>
                </div>
            </div>

            <div class="content-section">
                <h2 class="text-2xl font-bold mb-4">Challenge Information</h2>
                <ul class="space-y-2">
                    <li><strong>Challenge Name:</strong> Hiding in Plain Sight (Nothing Hidden Inside)</li>
                    <li><strong>Category:</strong> Steganography</li>
                    <li><strong>Points:</strong> 150 pts</li>
                    <li><strong>Teams Solved:</strong> 11</li>
                    <li><strong>Description:</strong> "Got this PDF from a crazy guy, wonder what he wants to tell me?"</li>
                    <li><strong>Hint:</strong> Not all is what it seems.</li>
                    <li><strong>Flag:</strong> <code class="text-green-600">EOF{u_r_@_ch!ck3n}</code></li>
                </ul>
            </div>

            <div class="content-section">
                <h2 class="text-2xl font-bold mb-4">Solution Methodology</h2>

                <h3 class="text-xl font-semibold mb-3 mt-4">Step 1: Initial Analysis</h3>
                <p class="mb-3">First, I tried opening the PDF normally — it showed nothing meaningful or just blank content. This hinted that the real information might not be visible through a regular PDF viewer.</p>
                <pre><code class="language-bash">ls -l Nothing_hidden_inside.pdf
# Confirmed file has reasonable size, suggesting hidden text</code></pre>

                <h3 class="text-xl font-semibold mb-3 mt-6">Step 2: Raw Content Inspection</h3>
                <p class="mb-3">Given the hint and the category (Steg), I decided to <strong>inspect the raw content</strong> of the file instead of viewing it normally.</p>
                <pre><code class="language-bash">cat Nothing_hidden_inside.pdf</code></pre>
                <p class="mb-3">Since PDF files can be quite verbose, I filtered for the end section (where PDF metadata or extra text might be hidden):</p>

                <h3 class="text-xl font-semibold mb-3 mt-6">Step 3: Search for Flag Pattern</h3>
                <pre><code class="language-bash">cat Nothing_hidden_inside.pdf | grep EOF</code></pre>

                <h3 class="text-xl font-semibold mb-3 mt-6">Step 4: Discovery</h3>
                <p class="mb-3">The command output revealed a series of characters just before the <code>%%EOF</code> marker:</p>
                <pre><code>{u_r_@_ch!ck3n}%</code></pre>
                <p class="mb-3">Following the given flag format (<code>EOF{}</code>), the flag becomes:</p>

                <div class="bg-green-50 border-l-4 border-green-400 p-4 mt-4">
                    <p class="font-semibold text-green-700"><strong>Flag:</strong> <code class="text-green-600">EOF{u_r_@_ch!ck3n}</code></p>
                    <p class="mt-2 text-sm">Translation: "You are a chicken" 🐔</p>
                </div>
            </div>

            <div class="content-section">
                <h2 class="text-2xl font-bold mb-4">Key Insights</h2>

                <h3 class="text-xl font-semibold mb-3">Why This Challenge Works</h3>
                <ul class="list-disc list-inside space-y-2 mb-4">
                    <li>PDF viewers don't display text hidden after the EOF marker</li>
                    <li>The <code>%%EOF</code> marker tells PDF readers where the file ends</li>
                    <li>Data after <code>%%EOF</code> is ignored by PDF readers but visible in raw content</li>
                    <li>Simple but effective steganography technique</li>
                </ul>

                <h3 class="text-xl font-semibold mb-3 mt-6">Tools Used</h3>
                <ul class="list-disc list-inside space-y-2">
                    <li><code>cat</code> - Display raw file content</li>
                    <li><code>grep</code> - Search for EOF pattern</li>
                    <li><code>strings</code> - Alternative for extracting readable text</li>
                </ul>

                <h3 class="text-xl font-semibold mb-3 mt-6">Alternative Methods</h3>
                <pre><code class="language-bash"># Method 1: Using strings
strings Nothing_hidden_inside.pdf | grep -i "eof"

# Method 2: Using tail (last lines)
tail -n 5 Nothing_hidden_inside.pdf

# Method 3: Using hex editor
hexdump -C Nothing_hidden_inside.pdf | tail -n 20</code></pre>
            </div>

            <div class="content-section">
                <h2 class="text-2xl font-bold mb-4">Summary Table</h2>
                <table>
                    <thead>
                        <tr>
                            <th>Step</th>
                            <th>Action</th>
                            <th>Result</th>
                        </tr>
                    </thead>
                    <tbody>
                        <tr>
                            <td>1</td>
                            <td>Opened PDF normally</td>
                            <td>Nothing visible</td>
                        </tr>
                        <tr>
                            <td>2</td>
                            <td>Used <code>cat</code> and <code>grep EOF</code></td>
                            <td>Revealed hidden text</td>
                        </tr>
                        <tr>
                            <td>3</td>
                            <td>Extracted flag in <code>EOF{}</code> format</td>
                            <td>Success!</td>
                        </tr>
                    </tbody>
                </table>
            </div>
        </div>
    </div>

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