Encrypt a model

Encrypt a model so that only a user with the correct key can read the model description and weights from disk. You can encrypt a Sentis model to disk using the ModelWriter and ModelLoader APIs.

Encrypt a model and save to disk

To encrypt a model and save it to disk, follow these steps, typically in the Unity Editor before building and distributing your project:

1. Get a Sentis model by importing an ONNX file or using the Sentis model API.
2. Create a Stream object for the encrypted model using a cryptography API with your key.
3. Encrypt and write the serialized model to the stream using the ModelWriter.Save method.

Certain types of streams such as MemoryStream may not be compatible with large models over 2GB.

Decrypt a model from disk

To decrypt a model from disk, follow these steps, usually before running the model:

1. Create a Stream object for the encrypted model using a cryptography API with your key.
2. Decrypt and deserialize the model using the ModelLoader.Load method.

Example using AES Encryption

The following code samples demonstrate how to serialize a runtime model to disk, encrypt it using the Advanced Encryption Standard (AES), and how to decrypt the encrypted model for inference.

This code sample uses AES encryption in C# to encrypt a model.

using System.IO;
using System.Security.Cryptography;
using Unity.Sentis;

void SaveModelAesEncrypted(Model model, string path, byte[] key)
{
    // Create a `FileStream` with the path of the encrypted asset
    using FileStream fileStream = new FileStream(path, FileMode.OpenOrCreate);
    using Aes aes = Aes.Create();
    aes.Key = key;

    byte[] iv = aes.IV;

    // Write the initialization vector to the file
    fileStream.Write(iv, 0, iv.Length);

    // Create a `CryptoStream` that writes to the `FileStream` 
    using CryptoStream cryptoStream = new CryptoStream(fileStream, aes.CreateEncryptor(), CryptoStreamMode.Write);

    // Serialize the model to the `CryptoStream`
    ModelWriter.Save(cryptoStream, model);
}

This code sample uses AES decryption in C# to decrypt a model.

using System.IO;
using System.Security.Cryptography;
using Unity.Sentis;

Model LoadModelAesEncrypted(string path, byte[] key)
{
    // Create a `FileStream` with the path of the encrypted asset
    using var fileStream = new FileStream(path, FileMode.Open);
    using Aes aes = Aes.Create();

    // Read the initialization vector from the file
    byte[] iv = new byte[aes.IV.Length];
    int numBytesToRead = aes.IV.Length;
    int numBytesRead = 0;
    while (numBytesToRead > 0)
    {
        int n = fileStream.Read(iv, numBytesRead, numBytesToRead);
        if (n == 0) break;

        numBytesRead += n;
        numBytesToRead -= n;
    }

    // Create a `CryptoStream` that reads from the `FileStream`
    using CryptoStream cryptoStream = new CryptoStream(fileStream, aes.CreateDecryptor(key, iv), CryptoStreamMode.Read);

    // Deserialize the model from the `CryptoStream`
    return ModelLoader.Load(cryptoStream);
}

Refer to the Encrypt a model example in the sample scripts for an example.