PixInWav: Residual Steganography for Hiding Pixels in Audio

This repository includes a python implemenation of StegoUNet, a deep neural network modelling an audio steganographic function.

Steganography comprises the mechanics of hiding secret data within a cover media which may be publicly available with the main premise that the fact that the communication is taking place is hidden as well.

If you find this paper or implementation useful, please consider citing our work:

@misc{geleta2021pixinwav,
      title={PixInWav: Residual Steganography for Hiding Pixels in Audio}, 
      author={Margarita Geleta and Cristina Punti and Kevin McGuinness and Jordi Pons and Cristian Canton and Xavier Giro-i-Nieto},
      year={2021},
      eprint={2106.09814},
      archivePrefix={arXiv},
      primaryClass={cs.MM}
}

Repository outline

In the src folder we find:

• umodel.py: the complete audio steganography model with RGB or B&W images as input.
• loader.py: the loader script to create the customized dataset from RGB or B&W image (ImageNet) + audio.
• trainer_rgb.py: a script to either train a model from scratch using provided training data or loading a pre-trained StegoUNet model for RGB or B&W images.
• losses.py: a script with all the losses and metrics defined for training. Uses a courtesy script to compute the SSIM metric.
• pystct.py: courtesy script to perform Short-Time Cosine Transform on raw audio waveforms.
• pydtw.py: courtesy script to compute SoftDTW as an additional term in the loss function.

In the scripts folder we find:

• train.sh: a sample sbatch script for Slurm used for sending training jobs.

Dependencies

First, create a virtual environment on your local repository and activate it:

$ python3 -m venv env
$ source env/bin/activate

The dependencies are listed in requirements.txt. Note that you need PyTorch v1.7.1 and TorchAudio v0.7.2. With pip installed, just run:

$ (env) pip3 install -r requirements.txt

Data

We use ImageNet (ILSVRC2012) 10,000 images for training and 900 images for validation. Regarding audio, we use FSDNoisy18K which has 17584 audios for training and 946 audios for validation. Each audio has a different duration, in our case we sample randomly different sections of audios that correspond to 1.5 seconds approximately (67522 samples).

Usage

After the installation of the requirements, to execute the trainer_rgb.py script, do:

$ (env) srun -u --gres=gpu:2,gpumem:12G 
        -p gpi.compute 
        --time 23:59:59 
        --mem 50G python3 trainer_rgb.py 
        --beta [beta_value] 
        --lr [learning_rate_value] 
        --summary "[description_of_the_run]" 
        --experiment [experiment_number]
        --add_noise [True/False]
        --noise_kind [gaussian/speckle/salt/pepper/salt&pepper]
        --noise_amplitude [float]
        --add_dtw_term [True/False]
        --rgb [use_rgb_or_b&w_images]
        --transform [cosine/fourier]
        --on_phase [if_fourier_hide_on_magnitude_or_phase]
        --architecture [resindep/resdep/resscale/plaindep]

Reserve as minimum 12G of GPU memory per GPU, otherwise you may be CUDA OOM. Or, run the sbatch script as follows:

$ (env) ./train.sh [experiment_number]

Defining all the arguments and hyperparameters in the script beforehand.

Loss function and optimization

• --lr defined the learning rate of the Adam optimizer.
• --beta determines the beta parameter of the loss function, refer to the paper for details.
• --add_dtw_term allows adding an additional term to the loss function. Adding it has shown improvements, refer to the paper for details.

Model architecture and constraints

• With --rgb you can choose to train on RGB or B&W images.
• --architecture allows to change the underlying architecture. It lists the 4 types of model explained in the paper, refer to it for more details.
• With --transform you can change the transform to obtain the audio spectrogram. Available transforms include STDCT (Short-Time Discrete Cosine Transform Type II) and STFT (Short-Time Fourier).
• If you use STFT, you can choose to hide the image in the magnitude or in the phase. You can control thos behaviour with --on_phase.

Noise addition

• For increasing the robustness of the steganographic function, you can add noise into the audio during training time with --add_noise.
• If you --add_noise then you should choose the --noise_kind and --noise_amplitude.

Monitor the training process

By default, wandb checkpoints are created when you execute the trainer_rgb.py script (you should login into your wandb account first). This allows tracking the learning curves in the web application.

If you prefer using tensorboard checkpoints, you will need to install tensorboardX and add the needed lines of code to save the values. Once it is done, just run in another shell window:

$ (env) tensorboard dev upload --logdir 'logs/[timestamp]'

Where logs is the directory you choose to store your logs.

Training from a checkpoint

To train a model from a checkpoint, follow these steps in the main function in trainer_rgb.py:

## Load the checkpoint
chk = torch.load('[checkpoint_path]/[checkpoint_name].pt', map_location='cpu')
model = StegoUNet()
model = nn.DataParallel(model)
## Load the weights into the model
model.load_state_dict(chk['state_dict'])

[...]

train(
    model=model, 
    tr_loader=train_loader, 
    vd_loader=test_loader, 
    beta=float(args.beta), 
    lr=float(args.lr), 
    epochs=15, 
    slide=15,
    prev_epoch=chk['epoch'], ## Specify this!
    prev_i=chk['i'], ## Specify this!
    summary=args.summary,
    experiment=int(args.experiment)
)

License

NOTICE: This software is available for use free of charge for academic research use only. Commercial users, for profit companies or consultants, and non-profit institutions not qualifying as academic research must contact [email protected] for a separate license.