code/attacks/base.py

"""Base class for Membership Inference Attacks."""

from abc import ABC, abstractmethod
from typing import Dict, Optional, Literal

import numpy as np

from mia.experiment import MIAExperiment
from mia.predictions import PredictionCache

AccessLevel = Literal["blackbox", "greybox", "whitebox"]


class BaseAttack(ABC):
    """
    Abstract base class for MIA attacks.

    Defines the interface for all attack implementations and provides
    common functionality for loading data.
    """

    def __init__(
        self,
        experiment: MIAExperiment,
        prediction_cache: PredictionCache,
        access_level: AccessLevel = "blackbox",
    ):
        """
        Initialize attack.

        Args:
            experiment: MIA experiment with membership matrices
            prediction_cache: Cache with model predictions
            access_level: Access level for the attack
        """
        self.experiment = experiment
        self.prediction_cache = prediction_cache
        self.access_level = access_level

    @property
    @abstractmethod
    def name(self) -> str:
        """Attack name for logging/display."""
        pass

    @abstractmethod
    def run(
        self,
        target_split: str = "target_test",
        num_target_models: Optional[int] = None,
        verbose: bool = True,
    ) -> Dict[str, np.ndarray]:
        """
        Run the attack on a target split.

        Args:
            target_split: Split to attack (target_train, target_val, target_test)
            num_target_models: Number of target models (None = all)
            verbose: Print progress

        Returns:
            Dictionary with:
                'scores': (num_samples,) aggregated membership scores
                'labels': (num_samples,) true membership labels
                'per_model_scores': (num_samples, num_models) individual scores
        """
        pass

    def get_shadow_data(self) -> Dict[str, np.ndarray]:
        """
        Get shadow model data for attack calibration.

        Returns:
            Dictionary with shadow model losses and membership matrix.
        """
        shadow_losses = self.prediction_cache.store["shadow"]["losses"][:, :]
        shadow_membership = self.experiment.get_membership_matrix("shadow").matrix
        return {
            "losses": shadow_losses,
            "membership": shadow_membership,
        }

    def get_target_data(
        self, split: str, num_models: Optional[int] = None
    ) -> Dict[str, np.ndarray]:
        """
        Get target model data for the attack.

        Args:
            split: Target split name
            num_models: Number of models (None = all)

        Returns:
            Dictionary with target losses, logits, and membership.
        """
        membership_matrix = self.experiment.get_membership_matrix(split)

        if num_models is None:
            num_models = membership_matrix.num_models

        target_losses = self.prediction_cache.store[split]["losses"][:, :num_models]
        target_logits = self.prediction_cache.store[split]["logits"][:, :num_models, :]

        return {
            "losses": target_losses,
            "logits": target_logits,
            "membership": membership_matrix,
            "num_models": num_models,
        }

    def compute_in_out_statistics(
        self,
        shadow_losses: np.ndarray,
        shadow_membership: np.ndarray,
    ) -> Dict[str, np.ndarray]:
        """
        Compute IN/OUT loss statistics from shadow models.

        Args:
            shadow_losses: (num_samples, num_shadow_models)
            shadow_membership: (num_samples, num_shadow_models) boolean

        Returns:
            Dictionary with in_mean, in_std, out_mean, out_std
        """
        in_mask = shadow_membership
        out_mask = ~shadow_membership

        in_losses_masked = np.where(in_mask, shadow_losses, np.nan)
        out_losses_masked = np.where(out_mask, shadow_losses, np.nan)

        return {
            "in_mean": np.nanmean(in_losses_masked, axis=1),
            "in_std": np.nanstd(in_losses_masked, axis=1) + 1e-10,
            "out_mean": np.nanmean(out_losses_masked, axis=1),
            "out_std": np.nanstd(out_losses_masked, axis=1) + 1e-10,
        }


class GreyBoxAttack(BaseAttack):
    """
    Base class for grey-box attacks with activation access.

    Extends BaseAttack with methods to load and use activation features.
    """

    def __init__(
        self,
        experiment: MIAExperiment,
        prediction_cache: PredictionCache,
        activation_cache=None,
    ):
        super().__init__(experiment, prediction_cache, access_level="greybox")
        self.activation_cache = activation_cache

    def get_shadow_activations(self) -> np.ndarray:
        """Get shadow model activations."""
        if self.activation_cache is None:
            raise ValueError("Activation cache not provided")
        return self.activation_cache.store["shadow"]["features"][:, :]

    def get_target_activations(
        self, split: str, num_models: Optional[int] = None
    ) -> np.ndarray:
        """Get target model activations."""
        if self.activation_cache is None:
            raise ValueError("Activation cache not provided")
        if num_models is None:
            return self.activation_cache.store[split]["features"][:, :]
        return self.activation_cache.store[split]["features"][:, :num_models, :]

    def compute_activation_statistics(
        self,
        shadow_activations: np.ndarray,
        shadow_membership: np.ndarray,
    ) -> Dict[str, np.ndarray]:
        """
        Compute IN/OUT activation statistics from shadow models.

        Args:
            shadow_activations: (num_samples, num_shadow_models, feature_dim)
            shadow_membership: (num_samples, num_shadow_models) boolean

        Returns:
            Dictionary with in_act_mean, in_act_std, out_act_mean, out_act_std
        """
        in_mask = shadow_membership[:, :, np.newaxis]  # (N, M, 1)
        out_mask = ~shadow_membership[:, :, np.newaxis]

        in_act_masked = np.where(in_mask, shadow_activations, np.nan)
        out_act_masked = np.where(out_mask, shadow_activations, np.nan)

        return {
            "in_act_mean": np.nanmean(in_act_masked, axis=1),  # (N, D)
            "in_act_std": np.nanstd(in_act_masked, axis=1) + 1e-10,
            "out_act_mean": np.nanmean(out_act_masked, axis=1),
            "out_act_std": np.nanstd(out_act_masked, axis=1) + 1e-10,
        }


class WhiteBoxAttack(GreyBoxAttack):
    """
    Base class for white-box attacks with gradient access.

    Extends GreyBoxAttack with methods to load and use gradient features.
    """

    def __init__(
        self,
        experiment: MIAExperiment,
        prediction_cache: PredictionCache,
        activation_cache=None,
        gradient_cache=None,
    ):
        super().__init__(experiment, prediction_cache, activation_cache)
        self.access_level = "whitebox"
        self.gradient_cache = gradient_cache

    def get_shadow_gradients(self) -> Dict[str, np.ndarray]:
        """Get shadow model gradient features."""
        if self.gradient_cache is None:
            raise ValueError("Gradient cache not provided")
        grp = self.gradient_cache.store["shadow"]
        return {
            "grad_norms": grp["grad_norms"][:, :],
            "grad_dot_weight": grp["grad_dot_weight"][:, :],
            "grad_features": grp["grad_features"][:, :, :],
        }

    def get_target_gradients(
        self, split: str, num_models: Optional[int] = None
    ) -> Dict[str, np.ndarray]:
        """Get target model gradient features."""
        if self.gradient_cache is None:
            raise ValueError("Gradient cache not provided")
        grp = self.gradient_cache.store[split]
        if num_models is None:
            return {
                "grad_norms": grp["grad_norms"][:, :],
                "grad_dot_weight": grp["grad_dot_weight"][:, :],
                "grad_features": grp["grad_features"][:, :, :],
            }
        return {
            "grad_norms": grp["grad_norms"][:, :num_models],
            "grad_dot_weight": grp["grad_dot_weight"][:, :num_models],
            "grad_features": grp["grad_features"][:, :num_models, :],
        }

    def compute_gradient_statistics(
        self,
        shadow_grad_norms: np.ndarray,
        shadow_membership: np.ndarray,
    ) -> Dict[str, np.ndarray]:
        """
        Compute IN/OUT gradient norm statistics from shadow models.

        Args:
            shadow_grad_norms: (num_samples, num_shadow_models)
            shadow_membership: (num_samples, num_shadow_models) boolean

        Returns:
            Dictionary with in_grad_mean, in_grad_std, out_grad_mean, out_grad_std
        """
        in_mask = shadow_membership
        out_mask = ~shadow_membership

        in_grad_masked = np.where(in_mask, shadow_grad_norms, np.nan)
        out_grad_masked = np.where(out_mask, shadow_grad_norms, np.nan)

        return {
            "in_grad_mean": np.nanmean(in_grad_masked, axis=1),
            "in_grad_std": np.nanstd(in_grad_masked, axis=1) + 1e-10,
            "out_grad_mean": np.nanmean(out_grad_masked, axis=1),
            "out_grad_std": np.nanstd(out_grad_masked, axis=1) + 1e-10,
        }