示例#1
0
 def test_xe_smoothing(self):
     loss = CrossEntropy(self.model, smoothing=0.1)
     l = loss.fprop(self.x, self.y)
     with tf.Session() as sess:
         vl1 = sess.run(l, feed_dict={self.x: self.vx, self.y: self.vy})
         vl2 = sess.run(l, feed_dict={self.x: self.vx, self.y: self.vy})
     self.assertClose(vl1, sum([2.10587597, 1.47194624]) / 2., atol=1e-6)
     self.assertClose(vl2, sum([2.10587597, 1.47194624]) / 2., atol=1e-6)
示例#2
0
 def test_xe(self):
     loss = CrossEntropy(self.model, smoothing=0.)
     l = loss.fprop(self.x, self.y)
     with tf.Session() as sess:
         vl1 = sess.run(l, feed_dict={self.x: self.vx, self.y: self.vy})
         vl2 = sess.run(l, feed_dict={self.x: self.vx, self.y: self.vy})
     self.assertClose(vl1, sum([2.210599660, 1.53666997]) / 2., atol=1e-6)
     self.assertClose(vl2, sum([2.210599660, 1.53666997]) / 2., atol=1e-6)
示例#3
0
def prep_bbox(sess,
              x,
              y,
              x_train,
              y_train,
              x_test,
              y_test,
              nb_epochs,
              batch_size,
              learning_rate,
              rng,
              nb_classes=10,
              img_rows=28,
              img_cols=28,
              nchannels=1):
    """
  Define and train a model that simulates the "remote"
  black-box oracle described in the original paper.
  :param sess: the TF session
  :param x: the input placeholder for MNIST
  :param y: the ouput placeholder for MNIST
  :param x_train: the training data for the oracle
  :param y_train: the training labels for the oracle
  :param x_test: the testing data for the oracle
  :param y_test: the testing labels for the oracle
  :param nb_epochs: number of epochs to train model
  :param batch_size: size of training batches
  :param learning_rate: learning rate for training
  :param rng: numpy.random.RandomState
  :return:
  """

    # Define TF model graph (for the black-box model)
    nb_filters = 64
    model = ModelBasicCNN('model1', nb_classes, nb_filters)
    loss = CrossEntropy(model, smoothing=0.1)
    predictions = model.get_logits(x)
    print("Defined TensorFlow model graph.")

    # Train an MNIST model
    train_params = {
        'nb_epochs': nb_epochs,
        'batch_size': batch_size,
        'learning_rate': learning_rate
    }
    train(sess, loss, x, y, x_train, y_train, args=train_params, rng=rng)

    # Print out the accuracy on legitimate data
    eval_params = {'batch_size': batch_size}
    accuracy = model_eval(sess,
                          x,
                          y,
                          predictions,
                          x_test,
                          y_test,
                          args=eval_params)
    print('Test accuracy of black-box on legitimate test '
          'examples: ' + str(accuracy))

    return model, predictions, accuracy
示例#4
0
def train_sub(sess,
              x,
              y,
              bbox_preds,
              x_sub,
              y_sub,
              nb_classes,
              nb_epochs_s,
              batch_size,
              learning_rate,
              data_aug,
              lmbda,
              aug_batch_size,
              rng,
              img_rows=28,
              img_cols=28,
              nchannels=1):
    """
  This function creates the substitute by alternatively
  augmenting the training data and training the substitute.
  :param sess: TF session
  :param x: input TF placeholder
  :param y: output TF placeholder
  :param bbox_preds: output of black-box model predictions
  :param x_sub: initial substitute training data
  :param y_sub: initial substitute training labels
  :param nb_classes: number of output classes
  :param nb_epochs_s: number of epochs to train substitute model
  :param batch_size: size of training batches
  :param learning_rate: learning rate for training
  :param data_aug: number of times substitute training data is augmented
  :param lmbda: lambda from arxiv.org/abs/1602.02697
  :param rng: numpy.random.RandomState instance
  :return:
  """
    # Define TF model graph (for the black-box model)
    model_sub = ModelSubstitute('model_s', nb_classes)
    preds_sub = model_sub.get_logits(x)
    loss_sub = CrossEntropy(model_sub, smoothing=0)

    print("Defined TensorFlow model graph for the substitute.")

    # Define the Jacobian symbolically using TensorFlow
    grads = jacobian_graph(preds_sub, x, nb_classes)

    # Train the substitute and augment dataset alternatively
    for rho in xrange(data_aug):
        print("Substitute training epoch #" + str(rho))
        train_params = {
            'nb_epochs': nb_epochs_s,
            'batch_size': batch_size,
            'learning_rate': learning_rate
        }
        with TemporaryLogLevel(logging.WARNING, "cleverhans.utils.tf"):
            train(sess,
                  loss_sub,
                  x,
                  y,
                  x_sub,
                  to_categorical(y_sub, nb_classes),
                  init_all=False,
                  args=train_params,
                  rng=rng,
                  var_list=model_sub.get_params())

        # If we are not at last substitute training iteration, augment dataset
        if rho < data_aug - 1:
            print("Augmenting substitute training data.")
            # Perform the Jacobian augmentation
            lmbda_coef = 2 * int(int(rho / 3) != 0) - 1
            x_sub = jacobian_augmentation(sess, x, x_sub, y_sub, grads,
                                          lmbda_coef * lmbda, aug_batch_size)

            print("Labeling substitute training data.")
            # Label the newly generated synthetic points using the black-box
            y_sub = np.hstack([y_sub, y_sub])
            x_sub_prev = x_sub[int(len(x_sub) / 2):]
            eval_params = {'batch_size': batch_size}
            bbox_val = batch_eval(sess, [x], [bbox_preds], [x_sub_prev],
                                  args=eval_params)[0]
            # Note here that we take the argmax because the adversary
            # only has access to the label (not the probabilities) output
            # by the black-box model
            y_sub[int(len(x_sub) / 2):] = np.argmax(bbox_val, axis=1)

    return model_sub, preds_sub
示例#5
0
def mnist_tutorial_jsma(train_start=0,
                        train_end=60000,
                        test_start=0,
                        test_end=10000,
                        viz_enabled=VIZ_ENABLED,
                        nb_epochs=NB_EPOCHS,
                        batch_size=BATCH_SIZE,
                        source_samples=SOURCE_SAMPLES,
                        learning_rate=LEARNING_RATE):
    """
  MNIST tutorial for the Jacobian-based saliency map approach (JSMA)
  :param train_start: index of first training set example
  :param train_end: index of last training set example
  :param test_start: index of first test set example
  :param test_end: index of last test set example
  :param viz_enabled: (boolean) activate plots of adversarial examples
  :param nb_epochs: number of epochs to train model
  :param batch_size: size of training batches
  :param nb_classes: number of output classes
  :param source_samples: number of test inputs to attack
  :param learning_rate: learning rate for training
  :return: an AccuracyReport object
  """
    # Object used to keep track of (and return) key accuracies
    report = AccuracyReport()

    # Set TF random seed to improve reproducibility
    tf.set_random_seed(1234)

    # Create TF session and set as Keras backend session
    sess = tf.Session()
    print("Created TensorFlow session.")

    set_log_level(logging.DEBUG)

    # Get MNIST test data
    x_train, y_train, x_test, y_test = data_mnist(train_start=train_start,
                                                  train_end=train_end,
                                                  test_start=test_start,
                                                  test_end=test_end)

    # Obtain Image Parameters
    img_rows, img_cols, nchannels = x_train.shape[1:4]
    nb_classes = y_train.shape[1]

    # Define input TF placeholder
    x = tf.placeholder(tf.float32, shape=(None, img_rows, img_cols, nchannels))
    y = tf.placeholder(tf.float32, shape=(None, nb_classes))

    nb_filters = 64
    # Define TF model graph
    model = ModelBasicCNN('model1', nb_classes, nb_filters)
    preds = model.get_logits(x)
    loss = CrossEntropy(model, smoothing=0.1)
    print("Defined TensorFlow model graph.")

    ###########################################################################
    # Training the model using TensorFlow
    ###########################################################################

    # Train an MNIST model
    train_params = {
        'nb_epochs': nb_epochs,
        'batch_size': batch_size,
        'learning_rate': learning_rate
    }
    sess.run(tf.global_variables_initializer())
    rng = np.random.RandomState([2017, 8, 30])
    train(sess, loss, x, y, x_train, y_train, args=train_params, rng=rng)

    # Evaluate the accuracy of the MNIST model on legitimate test examples
    eval_params = {'batch_size': batch_size}
    accuracy = model_eval(sess, x, y, preds, x_test, y_test, args=eval_params)
    assert x_test.shape[0] == test_end - test_start, x_test.shape
    print('Test accuracy on legitimate test examples: {0}'.format(accuracy))
    report.clean_train_clean_eval = accuracy

    ###########################################################################
    # Craft adversarial examples using the Jacobian-based saliency map approach
    ###########################################################################
    print('Crafting ' + str(source_samples) + ' * ' + str(nb_classes - 1) +
          ' adversarial examples')

    # Keep track of success (adversarial example classified in target)
    results = np.zeros((nb_classes, source_samples), dtype='i')

    # Rate of perturbed features for each test set example and target class
    perturbations = np.zeros((nb_classes, source_samples), dtype='f')

    # Initialize our array for grid visualization
    grid_shape = (nb_classes, nb_classes, img_rows, img_cols, nchannels)
    grid_viz_data = np.zeros(grid_shape, dtype='f')

    # Instantiate a SaliencyMapMethod attack object
    jsma = SaliencyMapMethod(model, back='tf', sess=sess)
    jsma_params = {
        'theta': 1.,
        'gamma': 0.1,
        'clip_min': 0.,
        'clip_max': 1.,
        'y_target': None
    }

    figure = None
    # Loop over the samples we want to perturb into adversarial examples
    for sample_ind in xrange(0, source_samples):
        print('--------------------------------------')
        print('Attacking input %i/%i' % (sample_ind + 1, source_samples))
        sample = x_test[sample_ind:(sample_ind + 1)]

        # We want to find an adversarial example for each possible target class
        # (i.e. all classes that differ from the label given in the dataset)
        current_class = int(np.argmax(y_test[sample_ind]))
        target_classes = other_classes(nb_classes, current_class)

        # For the grid visualization, keep original images along the diagonal
        grid_viz_data[current_class, current_class, :, :, :] = np.reshape(
            sample, (img_rows, img_cols, nchannels))

        # Loop over all target classes
        for target in target_classes:
            print('Generating adv. example for target class %i' % target)

            # This call runs the Jacobian-based saliency map approach
            one_hot_target = np.zeros((1, nb_classes), dtype=np.float32)
            one_hot_target[0, target] = 1
            jsma_params['y_target'] = one_hot_target
            adv_x = jsma.generate_np(sample, **jsma_params)

            # Check if success was achieved
            res = int(model_argmax(sess, x, preds, adv_x) == target)

            # Computer number of modified features
            adv_x_reshape = adv_x.reshape(-1)
            test_in_reshape = x_test[sample_ind].reshape(-1)
            nb_changed = np.where(adv_x_reshape != test_in_reshape)[0].shape[0]
            percent_perturb = float(nb_changed) / adv_x.reshape(-1).shape[0]

            # Display the original and adversarial images side-by-side
            if viz_enabled:
                figure = pair_visual(
                    np.reshape(sample, (img_rows, img_cols, nchannels)),
                    np.reshape(adv_x, (img_rows, img_cols, nchannels)), figure)

            # Add our adversarial example to our grid data
            grid_viz_data[target, current_class, :, :, :] = np.reshape(
                adv_x, (img_rows, img_cols, nchannels))

            # Update the arrays for later analysis
            results[target, sample_ind] = res
            perturbations[target, sample_ind] = percent_perturb

    print('--------------------------------------')

    # Compute the number of adversarial examples that were successfully found
    nb_targets_tried = ((nb_classes - 1) * source_samples)
    succ_rate = float(np.sum(results)) / nb_targets_tried
    print('Avg. rate of successful adv. examples {0:.4f}'.format(succ_rate))
    report.clean_train_adv_eval = 1. - succ_rate

    # Compute the average distortion introduced by the algorithm
    percent_perturbed = np.mean(perturbations)
    print('Avg. rate of perturbed features {0:.4f}'.format(percent_perturbed))

    # Compute the average distortion introduced for successful samples only
    percent_perturb_succ = np.mean(perturbations * (results == 1))
    print('Avg. rate of perturbed features for successful '
          'adversarial examples {0:.4f}'.format(percent_perturb_succ))

    # Close TF session
    sess.close()

    # Finally, block & display a grid of all the adversarial examples
    if viz_enabled:
        import matplotlib.pyplot as plt
        plt.close(figure)
        _ = grid_visual(grid_viz_data)

    return report
def mnist_tutorial(train_start=0, train_end=60000, test_start=0,
                   test_end=10000, nb_epochs=NB_EPOCHS, batch_size=BATCH_SIZE,
                   learning_rate=LEARNING_RATE,
                   clean_train=CLEAN_TRAIN,
                   testing=False,
                   backprop_through_attack=BACKPROP_THROUGH_ATTACK,
                   nb_filters=NB_FILTERS, num_threads=None,
                   label_smoothing=0.1):
  """
  MNIST cleverhans tutorial
  :param train_start: index of first training set example
  :param train_end: index of last training set example
  :param test_start: index of first test set example
  :param test_end: index of last test set example
  :param nb_epochs: number of epochs to train model
  :param batch_size: size of training batches
  :param learning_rate: learning rate for training
  :param clean_train: perform normal training on clean examples only
                      before performing adversarial training.
  :param testing: if true, complete an AccuracyReport for unit tests
                  to verify that performance is adequate
  :param backprop_through_attack: If True, backprop through adversarial
                                  example construction process during
                                  adversarial training.
  :param label_smoothing: float, amount of label smoothing for cross entropy
  :return: an AccuracyReport object
  """

  # Object used to keep track of (and return) key accuracies
  report = AccuracyReport()

  # Set TF random seed to improve reproducibility
  tf.set_random_seed(1234)

  # Set logging level to see debug information
  set_log_level(logging.DEBUG)

  # Create TF session
  if num_threads:
    config_args = dict(intra_op_parallelism_threads=1)
  else:
    config_args = {}
  sess = tf.Session(config=tf.ConfigProto(**config_args))

  # Get MNIST test data
  x_train, y_train, x_test, y_test = data_mnist(train_start=train_start,
                                                train_end=train_end,
                                                test_start=test_start,
                                                test_end=test_end)
  # Use Image Parameters
  img_rows, img_cols, nchannels = x_train.shape[1:4]
  nb_classes = y_train.shape[1]

  # Define input TF placeholder
  x = tf.placeholder(tf.float32, shape=(None, img_rows, img_cols,
                                        nchannels))
  y = tf.placeholder(tf.float32, shape=(None, nb_classes))

  # Train an MNIST model
  train_params = {
      'nb_epochs': nb_epochs,
      'batch_size': batch_size,
      'learning_rate': learning_rate
  }
  eval_params = {'batch_size': batch_size}
  fgsm_params = {
      'eps': 0.3,
      'clip_min': 0.,
      'clip_max': 1.
  }
  rng = np.random.RandomState([2017, 8, 30])

  def do_eval(preds, x_set, y_set, report_key, is_adv=None):
    acc = model_eval(sess, x, y, preds, x_set, y_set, args=eval_params)
    setattr(report, report_key, acc)
    if is_adv is None:
      report_text = None
    elif is_adv:
      report_text = 'adversarial'
    else:
      report_text = 'legitimate'
    if report_text:
      print('Test accuracy on %s examples: %0.4f' % (report_text, acc))

  if clean_train:
    model = ModelBasicCNN('model1', nb_classes, nb_filters)
    preds = model.get_logits(x)
    loss = CrossEntropy(model, smoothing=label_smoothing)

    def evaluate():
      do_eval(preds, x_test, y_test, 'clean_train_clean_eval', False)

    train(sess, loss, x, y, x_train, y_train, evaluate=evaluate,
          args=train_params, rng=rng, var_list=model.get_params())

    # Calculate training error
    if testing:
      do_eval(preds, x_train, y_train, 'train_clean_train_clean_eval')

    # Initialize the Fast Gradient Sign Method (FGSM) attack object and
    # graph
    fgsm = FastGradientMethod(model, sess=sess)
    adv_x = fgsm.generate(x, **fgsm_params)
    preds_adv = model.get_logits(adv_x)

    # Evaluate the accuracy of the MNIST model on adversarial examples
    do_eval(preds_adv, x_test, y_test, 'clean_train_adv_eval', True)

    # Calculate training error
    if testing:
      do_eval(preds_adv, x_train, y_train, 'train_clean_train_adv_eval')

    print('Repeating the process, using adversarial training')

  # Create a new model and train it to be robust to FastGradientMethod
  model2 = ModelBasicCNN('model2', nb_classes, nb_filters)
  fgsm2 = FastGradientMethod(model2, sess=sess)

  def attack(x):
    return fgsm2.generate(x, **fgsm_params)

  loss2 = CrossEntropy(model2, smoothing=label_smoothing, attack=attack)
  preds2 = model2.get_logits(x)
  adv_x2 = attack(x)

  if not backprop_through_attack:
    # For the fgsm attack used in this tutorial, the attack has zero
    # gradient so enabling this flag does not change the gradient.
    # For some other attacks, enabling this flag increases the cost of
    # training, but gives the defender the ability to anticipate how
    # the atacker will change their strategy in response to updates to
    # the defender's parameters.
    adv_x2 = tf.stop_gradient(adv_x2)
  preds2_adv = model2.get_logits(adv_x2)

  def evaluate2():
    # Accuracy of adversarially trained model on legitimate test inputs
    do_eval(preds2, x_test, y_test, 'adv_train_clean_eval', False)
    # Accuracy of the adversarially trained model on adversarial examples
    do_eval(preds2_adv, x_test, y_test, 'adv_train_adv_eval', True)

  # Perform and evaluate adversarial training
  train(sess, loss2, x, y, x_train, y_train, evaluate=evaluate2,
        args=train_params, rng=rng, var_list=model2.get_params())

  # Calculate training errors
  if testing:
    do_eval(preds2, x_train, y_train, 'train_adv_train_clean_eval')
    do_eval(preds2_adv, x_train, y_train, 'train_adv_train_adv_eval')

  return report
def mnist_tutorial_cw(train_start=0, train_end=60000, test_start=0,
                      test_end=10000, viz_enabled=VIZ_ENABLED,
                      nb_epochs=NB_EPOCHS, batch_size=BATCH_SIZE,
                      source_samples=SOURCE_SAMPLES,
                      learning_rate=LEARNING_RATE,
                      attack_iterations=ATTACK_ITERATIONS,
                      model_path=MODEL_PATH,
                      targeted=TARGETED):
  """
  MNIST tutorial for Carlini and Wagner's attack
  :param train_start: index of first training set example
  :param train_end: index of last training set example
  :param test_start: index of first test set example
  :param test_end: index of last test set example
  :param viz_enabled: (boolean) activate plots of adversarial examples
  :param nb_epochs: number of epochs to train model
  :param batch_size: size of training batches
  :param nb_classes: number of output classes
  :param source_samples: number of test inputs to attack
  :param learning_rate: learning rate for training
  :param model_path: path to the model file
  :param targeted: should we run a targeted attack? or untargeted?
  :return: an AccuracyReport object
  """
  # Object used to keep track of (and return) key accuracies
  report = AccuracyReport()

  # Set TF random seed to improve reproducibility
  tf.set_random_seed(1234)

  # Create TF session
  sess = tf.Session()
  print("Created TensorFlow session.")

  set_log_level(logging.DEBUG)

  # Get MNIST test data
  x_train, y_train, x_test, y_test = data_mnist(train_start=train_start,
                                                train_end=train_end,
                                                test_start=test_start,
                                                test_end=test_end)

  # Obtain Image Parameters
  img_rows, img_cols, nchannels = x_train.shape[1:4]
  nb_classes = y_train.shape[1]

  # Define input TF placeholder
  x = tf.placeholder(tf.float32, shape=(None, img_rows, img_cols,
                                        nchannels))
  y = tf.placeholder(tf.float32, shape=(None, nb_classes))
  nb_filters = 64

  # Define TF model graph
  model = ModelBasicCNN('model1', nb_classes, nb_filters)
  preds = model.get_logits(x)
  loss = CrossEntropy(model, smoothing=0.1)
  print("Defined TensorFlow model graph.")

  ###########################################################################
  # Training the model using TensorFlow
  ###########################################################################

  # Train an MNIST model
  train_params = {
      'nb_epochs': nb_epochs,
      'batch_size': batch_size,
      'learning_rate': learning_rate,
      'filename': os.path.split(model_path)[-1]
  }

  rng = np.random.RandomState([2017, 8, 30])
  # check if we've trained before, and if we have, use that pre-trained model
  if os.path.exists(model_path + ".meta"):
    tf_model_load(sess, model_path)
  else:
    train(sess, loss, x, y, x_train, y_train, args=train_params, rng=rng)
    saver = tf.train.Saver()
    saver.save(sess, model_path)

  # Evaluate the accuracy of the MNIST model on legitimate test examples
  eval_params = {'batch_size': batch_size}
  accuracy = model_eval(sess, x, y, preds, x_test, y_test, args=eval_params)
  assert x_test.shape[0] == test_end - test_start, x_test.shape
  print('Test accuracy on legitimate test examples: {0}'.format(accuracy))
  report.clean_train_clean_eval = accuracy

  ###########################################################################
  # Craft adversarial examples using Carlini and Wagner's approach
  ###########################################################################
  nb_adv_per_sample = str(nb_classes - 1) if targeted else '1'
  print('Crafting ' + str(source_samples) + ' * ' + nb_adv_per_sample +
        ' adversarial examples')
  print("This could take some time ...")

  # Instantiate a CW attack object
  cw = CarliniWagnerL2(model, back='tf', sess=sess)

  if viz_enabled:
    assert source_samples == nb_classes
    idxs = [np.where(np.argmax(y_test, axis=1) == i)[0][0]
            for i in range(nb_classes)]
  if targeted:
    if viz_enabled:
      # Initialize our array for grid visualization
      grid_shape = (nb_classes, nb_classes, img_rows, img_cols,
                    nchannels)
      grid_viz_data = np.zeros(grid_shape, dtype='f')

      adv_inputs = np.array(
          [[instance] * nb_classes for instance in x_test[idxs]],
          dtype=np.float32)
    else:
      adv_inputs = np.array(
          [[instance] * nb_classes for
           instance in x_test[:source_samples]], dtype=np.float32)

    one_hot = np.zeros((nb_classes, nb_classes))
    one_hot[np.arange(nb_classes), np.arange(nb_classes)] = 1

    adv_inputs = adv_inputs.reshape(
        (source_samples * nb_classes, img_rows, img_cols, nchannels))
    adv_ys = np.array([one_hot] * source_samples,
                      dtype=np.float32).reshape((source_samples *
                                                 nb_classes, nb_classes))
    yname = "y_target"
  else:
    if viz_enabled:
      # Initialize our array for grid visualization
      grid_shape = (nb_classes, 2, img_rows, img_cols, nchannels)
      grid_viz_data = np.zeros(grid_shape, dtype='f')

      adv_inputs = x_test[idxs]
    else:
      adv_inputs = x_test[:source_samples]

    adv_ys = None
    yname = "y"

  if targeted:
    cw_params_batch_size = source_samples * nb_classes
  else:
    cw_params_batch_size = source_samples
  cw_params = {'binary_search_steps': 1,
               yname: adv_ys,
               'max_iterations': attack_iterations,
               'learning_rate': CW_LEARNING_RATE,
               'batch_size': cw_params_batch_size,
               'initial_const': 10}

  adv = cw.generate_np(adv_inputs,
                       **cw_params)

  eval_params = {'batch_size': np.minimum(nb_classes, source_samples)}
  if targeted:
    adv_accuracy = model_eval(
        sess, x, y, preds, adv, adv_ys, args=eval_params)
  else:
    if viz_enabled:
      err = model_eval(sess, x, y, preds, adv, y_test[idxs], args=eval_params)
      adv_accuracy = 1 - err
    else:
      err = model_eval(sess, x, y, preds, adv, y_test[:source_samples],
                       args=eval_params)
      adv_accuracy = 1 - err

  if viz_enabled:
    for j in range(nb_classes):
      if targeted:
        for i in range(nb_classes):
          grid_viz_data[i, j] = adv[i * nb_classes + j]
      else:
        grid_viz_data[j, 0] = adv_inputs[j]
        grid_viz_data[j, 1] = adv[j]

    print(grid_viz_data.shape)

  print('--------------------------------------')

  # Compute the number of adversarial examples that were successfully found
  print('Avg. rate of successful adv. examples {0:.4f}'.format(adv_accuracy))
  report.clean_train_adv_eval = 1. - adv_accuracy

  # Compute the average distortion introduced by the algorithm
  percent_perturbed = np.mean(np.sum((adv - adv_inputs)**2,
                                     axis=(1, 2, 3))**.5)
  print('Avg. L_2 norm of perturbations {0:.4f}'.format(percent_perturbed))

  # Close TF session
  sess.close()

  # Finally, block & display a grid of all the adversarial examples
  if viz_enabled:
    import matplotlib.pyplot as plt
    _ = grid_visual(grid_viz_data)

  return report