🔐 CyberStegoApp — Android Image Steganography (Java)

Hide AES‑encrypted text inside images using LSB steganography. Share, save, and extract securely.

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📱 What It Does

StegoApp lets you embed a secret message into an image. The message is first AES‑encrypted, then written bit‑by‑bit into pixel data using Least Significant Bit (LSB). With the same key, the ciphertext is extracted and decrypted back to the original message.

Key features:

• Login/Signup with persistent session (SharedPreferences)
• Tabs: Embedding, Extraction, User info
• Share embedded images to other apps
• Delete account from User info
• Shake‑to‑logout using accelerometer

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🏗️ Project Structure

com.example.stegoapp
│
├── LoginActivity.java        // Login + auto-redirect if already logged in
├── SignupActivity.java       // New user registration
├── MainActivity.java         // Tabs: Embedding / Extraction / User info
│
├── ui/
│   ├── EmbeddingFragment.java   // Pick image → encrypt → center-crop square → embed → save/share
│   ├── ExtractionFragment.java  // Pick image → center-crop square → extract → decrypt
│   └── UserInfoFragment.java    // Show username/password, logout, delete account
│
├── crypto/CryptoUtils.java      // AES-128 (ECB/PKCS5Padding), 16-byte normalized key
├── stego/StegoUtils.java        // LSB embed/extract, 32-bit length header, center-square
├── util/ImageUtils.java         // Software ARGB_8888 decode + PNG save (MediaStore)
├── util/ExecutorProvider.java   // Shared single-thread executor for DB work
│
├── data/
│   ├── AppDatabase.java         // Room database (users table), singleton
│   ├── User.java                // Room entity: username (PK, non-null), password (plain for demo)
│   └── UserDao.java             // DAO: insert/find/deleteByUsername
│
└── res/layout/...               // activity_main, fragment_* and auth screens

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🔄 App Flow

Launch
  └─► LoginActivity
        ├─► [session exists] ───────────► MainActivity (tabs)
        └─► [no session] login or signup

MainActivity (Tabs)
  ├─► Embedding
  │     1) Pick image (any format; saved as PNG)
  │     2) Enter message + key
  │     3) AES encrypt → center-square crop → LSB embed
  │     4) Save or Share (document share to avoid recompression)
  │
  ├─► Extraction
  │     1) Pick image (recommend PNG)
  │     2) Center-square crop → read bits → AES decrypt
  │     3) Show message (errors if image was recompressed)
  │
  └─► User info
        - View username/password (demo)
        - Logout
        - Delete account (removes current user + logs out)

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🖼️ Steganography

Center‑Square + LSB

• If the chosen image is rectangular (e.g., 1600×900), the app crops the center square (900×900).
• Embedding starts at the first pixel of the square (i.e., the visual center of the original image area).
• Each pixel contributes one bit via the blue channel’s least significant bit.

Data Format

[4 bytes: payload bit length] [N bytes: AES ciphertext]

Capacity

• Bits available = (squareWidth × squareHeight) − 32
• Bytes available ≈ floor(Bits / 8)

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🔑 Encryption

Property	Value
Algorithm	AES
Mode	ECB
Padding	PKCS5
Key Size	128‑bit (16 bytes)
Key Handling	Input is UTF‑8; padded with zeros or truncated to 16 bytes
IV	None (ECB)

Note: ECB is used for simplicity in this demo. For stronger security, consider AES‑GCM with an IV stored alongside ciphertext (requires changing extraction format).

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🗄️ Database & Session

• Room table users:
  • username (TEXT, PK, non‑null)
  • password (TEXT, demo only — do not use plain text in production)
• Session via SharedPreferences:
  • logged_user → current username or null

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📤 Sharing Notes

Some apps (e.g., WhatsApp image share) recompress images and destroy LSB data. StegoApp’s Share uses a generic MIME (*/*) so targets treat it like a document, preserving the PNG bytes. When extracting, if the app detects an invalid length header or capacity mismatch, it reports that no hidden data is present (likely recompressed).

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🛠️ Tech Stack

Component	Technology
Language	Java
Min/Target SDK	24 / 34
Build	Gradle 8.5, AGP 8.3
DB	Room (SQLite)
Crypto	javax.crypto
Session	SharedPreferences
UI	AppCompat + Material Components

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🚀 Setup

1. Open the project in Android Studio.
2. Ensure Gradle JDK is 17 (or 21 with Gradle 8.5+).
3. Sync and Run on an emulator/device (API 24+).

No storage permission is required on Android 10+ when picking images via the system picker. MediaStore is used to save PNGs.

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🧪 Quick Test

1. Sign up a user → login.
2. Embedding tab → pick image → enter message + key → Embed.
3. Save or Share the embedded image.
4. Extraction tab → pick the saved/shared image → enter key → Decrypt.
5. Message appears if the image wasn’t recompressed.

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⚠️ Notes

• Use PNG or “document” sharing to avoid recompression. JPEG/WebP may destroy hidden bits.
• Passwords are stored in plain text for demo simplicity — do not use in production.
• Center‑square embedding affects output size; the saved embedded image is the cropped square.

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Built as a concise, fast Android steganography demo using LSB + AES encryption.