client_server.md

Production Deployment

This document explains the deployment workflow and the model serving pattern for deploying Fully Homomorphic Encryption machine learning models in a client/server setting using Concrete ML.

Deployment

The steps to prepare a model for encrypted inference in a client/server setting is illustrated as follows:

Model training and compilation

The training of the model and its compilation to FHE are performed on a development machine.

Three different files are created when saving the model:

• client.zip contains the following files:
  • client.specs.json lists the secure cryptographic parameters needed for the client to generate private and evaluation keys.
  • serialized_processing.json describes the pre-processing and post-processing required by the machine learning model, such as quantization parameters to quantize the input and de-quantize the output.
• server.zip contains the compiled model. This file is sufficient to run the model on a server. The compiled model is machine-architecture specific, for example, a model compiled on x86 cannot run on ARM.

Model deployment

The compiled model (server.zip) is deployed to a server. The cryptographic parameters (client.zip) are shared with the clients. In some settings, such as a phone application, the client.zip can be directly deployed on the client device and the server does not need to host it.

{% hint style="info" %} Important: In a client-server production using FHE, the server's output format depends on the model type:

• For regressors, the output matches the predict() method from scikit-learn, providing direct predictions.
• For classifiers, the output uses the predict_proba() method format, offering probability scores for each class, which allows clients to determine class membership by applying a threshold (commonly 0.5). {% endhint %}

Using the API Classes

The FHEModelDev, FHEModelClient, and FHEModelServer classes in the concrete.ml.deployment module simplifies the deployment and interaction between the client and server:

• FHEModelDev:

  • This class handles the serialization of the underlying FHE circuit as well as the crypto-parameters used for generating the keys.
  • Use the save method of this class during the development phase to prepare and save the model artifacts (client.zip and server.zip). With save method, you can deploy a trained model or a training FHE program.

• FHEModelClient is used on the client side for the following actions:

  • Generate and serialize the cryptographic keys.
  • Encrypt the data before sending it to the server.
  • Decrypt the results received from the server.
  • Load quantization parameters and pre/post-processing from serialized_processing.json.

• FHEModelServer is used on the server side for the following actions:

  • Load the FHE circuit from server.zip .
  • Execute the model on encrypted data received from the client.

Example Usage

from concrete.ml.sklearn import DecisionTreeClassifier
from concrete.ml.deployment import FHEModelDev, FHEModelClient, FHEModelServer
import numpy as np

# Define the directory for FHE client/server files
fhe_directory = '/tmp/fhe_client_server_files/'

# Initialize the Decision Tree model
model = DecisionTreeClassifier()

# Generate some random data for training
X = np.random.rand(100, 20)
y = np.random.randint(0, 2, size=100)

# Train and compile the model
model.fit(X, y)
model.compile(X)

# Setup the development environment
dev = FHEModelDev(path_dir=fhe_directory, model=model)
dev.save()

# Setup the client
client = FHEModelClient(path_dir=fhe_directory, key_dir="/tmp/keys_client")
serialized_evaluation_keys = client.get_serialized_evaluation_keys()

# Client pre-processes new data
X_new = np.random.rand(1, 20)
encrypted_data = client.quantize_encrypt_serialize(X_new)

# Setup the server
server = FHEModelServer(path_dir=fhe_directory)
server.load()

# Server processes the encrypted data
encrypted_result = server.run(encrypted_data, serialized_evaluation_keys)

# Client decrypts the result
result = client.deserialize_decrypt_dequantize(encrypted_result)

Data transfer overview:

• From Client to Server: serialized_evaluation_keys (once), encrypted_data.
• From Server to Client: encrypted_result.

These objects are serialized into bytes to streamline the data transfer between the client and server.

Serving

The client-side deployment of a secured inference machine learning model is illustrated as follows:

The workflow contains the following steps:

1. Key generation: The client obtains the cryptographic parameters stored in client.zip and generates a private encryption/decryption key as well as a set of public evaluation keys.
2. Sending public keys: The public evaluation keys are sent to the server, while the secret key remains on the client.
3. Data encryption: The private data is encrypted by the client as described in the serialized_processing.json file in client.zip.
4. Data transmission: The encrypted data is sent to the server.
5. Encrypted inference: Server-side, the FHE model inference is run on encrypted inputs using the public evaluation keys.
6. Data transmission: The encrypted result is returned by the server to the client.
7. Data decryption: The client decrypts it using its private key.
8. Post-processing: The client performs any necessary post-processing of the decrypted result as specified in serialized_processing.json (part of client.zip).

The server-side implementation of a Concrete ML model is illustrated as follows:

The workflow contains the following steps:

1. Storing the public key: The public evaluation keys sent by clients are stored.
2. Model evaluation: The public evaluation keys are retrieved for the client that is querying the service and used to evaluate the machine learning model stored in server.zip.
3. Sending back the result: The server sends the encrypted result of the computation back to the client.

Example notebook

For a complete example, see the client-server notebook or the use-case examples.