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 an Inference Engine model to disk with the ModelWriter and ModelLoader APIs.

Encrypt a model and save to disk

Use the following steps to encrypt and save a model to disk, typically in the Unity Editor before you build and distribute your project:

  1. To get an Inference Engine model, import an ONNX file or use the Inference Engine model API.
  2. Create a Stream object for the encrypted model with a cryptography API and your encryption key.
  3. Call ModelWriter.Save to serialize and encrypt the model to the stream.
Note

Certain stream types, such as MemoryStream, might not support large models over 2 GB.

Decrypt a model from disk

To decrypt and load a model before you run it, follow these steps:

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

Example: encrypt and decrypt a model with AES

The following code samples demonstrate how to serialize a runtime model to disk, encrypt it with the Advanced Encryption Standard (AES), and then 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.InferenceEngine;

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.InferenceEngine;

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);
}

For an example, refer to the Encrypt a model example in the sample scripts for an example.

Additional resources