steganography

Flutter plugin and CLI tool: encrypt UTF-8 text (AES-256-GCM or GOST Magma CTR) and hide it inside PNG/JPEG images using native steganography on Android and iOS, with a desktop terminal interface for development and offline use.

What it does

Text (UTF-8)
    ↓ encrypt (AES-256-GCM or GOST Magma CTR)
Encrypted payload
    ↓ pack (STG1 / STG2 / STG4 header)
Binary payload
    ↓ embed (LSB or JPEG-DCT)
Stego image (PNG or JPEG)

Decryption reverses the pipeline. The same 32-byte key and steganography method must be used for both embed and extract.

Features

• Four steganography methods
  • lsb — least significant bits in RGB channels (high capacity, PNG output)
  • dct — JPEG luma DCT coefficients, 1 bit per 8×8 block
  • telegramRobust2 — robust DCT for lossy messengers (resize to 1280 px + JPEG Q80)
  • dctResidualModulation — survives heavy social-network recompression
• Two ciphers: AES-256-GCM (default) and GOST R 34.12-2015 Magma (CTR)
• Carriers: PNG and JPEG
• Native JPEG layer: libjpeg-turbo coefficient-domain embedding (C++/Kotlin/Swift)
• CLI: terminal commands for embed/extract on macOS/Linux (LSB in pure Dart; DCT methods via FFI)

Installation

dependencies:
  steganography: ^0.1.0

import 'package:steganography/steganography.dart';

Quick start (Flutter)

import 'dart:typed_data';
import 'package:steganography/steganography.dart';

final key = Uint8List.fromList(List.filled(32, 0x42)); // 256-bit key

final controller = SteganographyController(
  key: key,
  method: SteganographyMethod.lsb,
  cipher: SteganographyCipher.aes256Gcm,
);

// Embed text into a carrier image
final stegoBytes = await controller.encrypt(
  imageBytes: carrierPngOrJpeg,
  text: 'Secret message',
);

// Extract (same key + method)
final text = await controller.decrypt(imageBytes: stegoBytes);

controller.dispose(); // zeroes the key in memory

Choosing a method

Method	Capacity	Robustness	Output format	Best for
lsb	High	Low (lossless only)	PNG	Maximum payload size
dct	~1 bit / 8×8 block	Moderate	JPEG	Standard JPEG workflow
telegramRobust2	Lower (Hamming + repetition)	High	JPEG	Telegram-like messengers
dctResidualModulation	Lowest	Highest	JPEG	Aggressive recompression

Choosing a cipher

Cipher	Description
aes256Gcm	AES-256-GCM: 12-byte nonce + ciphertext + 16-byte MAC
gostMagmaCtr	GOST R 34.12-2015 «Магма» in CTR mode, 256-bit key

Platform support

Platform	Min version	Embed / extract
Android	API 21	All four methods
iOS	12.0	All four methods
macOS / Linux (CLI)	—	lsb, dct, telegramRobust2
Web / Windows / desktop Flutter	—	Not supported

Example app

cd example
flutter pub get
flutter run

The example app lets you pick an image from the gallery, choose method and cipher, embed text, and extract it back.

Command-line tool

Run embed/extract from the terminal without the Flutter app. Useful for scripting, testing, and decrypting stego images on a desktop.

CLI method support

Method	Engine	Input	Output	Native build
lsb	Pure Dart	PNG	PNG	Not required
dct	FFI (C++)	PNG / JPEG	JPEG	Required
telegramRobust2	FFI (C++)	PNG / JPEG / etc.	JPEG	Required
dctResidualModulation	—	—	—	Not available in CLI yet

Stego files produced by the CLI are compatible with the mobile plugin (and vice versa) when the same key, method, and cipher are used.

Setup

cd steganography
dart pub get

# One-time: build native library for DCT methods (macOS / Linux)
bash tool/build_native.sh
# → native/build/libjpegstego.dylib  (or .so on Linux)

Commands

# Encrypt / embed (aliases: encrypt, embed)
dart run steganography encrypt \
  -i cover.png \
  -o stego.png \
  -k <key> \
  -m "secret message"

# LSB — no native build needed
dart run steganography encrypt -i cover.png -o stego.png -k <key> -m "hello"

# DCT — needs a large enough image (~1024×1024 for short messages)
dart run steganography encrypt -i photo.jpg -o stego.jpg -k <key> -m "hello" --method dct

# TelegramRobust2
dart run steganography encrypt -i cover.png -o stego.jpg -k <key> -m "hi" --method telegramRobust2

# Decrypt / extract (aliases: decrypt, extract)
dart run steganography decrypt -i stego.jpg -k <key> --method dct

# Read message from a file
dart run steganography encrypt -i cover.png -o stego.png -k <key> -m @message.txt

# GOST Magma instead of AES
dart run steganography encrypt -i cover.png -o stego.png -k <key> -m "secret" --cipher gost

Key format (-k)

Format	Example
64 hex digits (32 bytes)	deadbeef… (64 characters)
Path to a 32-byte key file	-k ./my.key
UTF-8 string, exactly 32 chars	-k 12345678901234567890123456789012

CLI options

Flag	Commands	Description
-i, --input	all	Path to input image
-o, --output	encrypt	Path to output stego image
-k, --key	all	Encryption key (see formats above)
-m, --message	encrypt	Text to hide (@file to read from file)
--method	all	lsb (default), dct, telegramRobust2
--cipher	encrypt	aes (default) or gost

Environment variables

# Custom path to the native shared library
export STEGANOGRAPHY_NATIVE_LIB=/path/to/libjpegstego.dylib

CLI limitations

• DCT capacity: 1 bit per 8×8 JPEG block — use a large carrier (e.g. 1024×1024) for messages longer than a few bytes.
• TelegramRobust2 extract re-encodes the image to JPEG Q80 (same as on mobile). Cross-platform JPEG encoders may differ slightly.
• Native build is tested on macOS and Linux; Windows may work via CMake but is not verified.

Development

flutter pub get
flutter analyze
flutter test

Integration tests (device / emulator):

cd example
flutter test integration_test/plugin_integration_test.dart

Rebuild the desktop native library after C++ changes:

bash tool/build_native.sh

Project structure

lib/
  steganography.dart              # Public API
  public/                       # SteganographyController, enums
  internal/                     # Crypto, payload format, method channel
  cli/                          # Terminal tool (LSB + FFI JPEG)
bin/steganography.dart            # CLI entry point
android/src/main/cpp/           # Native JPEG stego (CMake + JNI)
ios/jpeg_stego/                 # Same C++ sources for iOS
native/                         # Desktop CMake build for CLI FFI
example/                        # Demo Flutter app

License

MIT — see LICENSE.