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mannequin inversion assault by instance

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How non-public are particular person information within the context of machine studying fashions? The info used to coach the mannequin, say. There are sorts of fashions the place the reply is easy. Take k-nearest-neighbors, for instance. There shouldn’t be even a mannequin with out the whole dataset. Or help vector machines. There isn’t a mannequin with out the help vectors. However neural networks? They’re just a few composition of features, – no information included.

The identical is true for information fed to a deployed deep-learning mannequin. It’s fairly unlikely one might invert the ultimate softmax output from an enormous ResNet and get again the uncooked enter information.

In concept, then, “hacking” a typical neural internet to spy on enter information sounds illusory. In apply, nonetheless, there may be all the time some real-world context. The context could also be different datasets, publicly out there, that may be linked to the “non-public” information in query. This can be a widespread showcase utilized in advocating for differential privateness(Dwork et al. 2006): Take an “anonymized” dataset, dig up complementary data from public sources, and de-anonymize data advert libitum. Some context in that sense will typically be utilized in “black-box” assaults, ones that presuppose no insider details about the mannequin to be hacked.

However context may also be structural, resembling within the situation demonstrated on this publish. For instance, assume a distributed mannequin, the place units of layers run on completely different units – embedded units or cellphones, for instance. (A situation like that’s typically seen as “white-box”(Wu et al. 2016), however in widespread understanding, white-box assaults in all probability presuppose some extra insider data, resembling entry to mannequin structure and even, weights. I’d subsequently desire calling this white-ish at most.) — Now assume that on this context, it’s potential to intercept, and work together with, a system that executes the deeper layers of the mannequin. Primarily based on that system’s intermediate-level output, it’s potential to carry out mannequin inversion(Fredrikson et al. 2014), that’s, to reconstruct the enter information fed into the system.

On this publish, we’ll display such a mannequin inversion assault, principally porting the method given in a pocket book discovered within the PySyft repository. We then experiment with completely different ranges of (epsilon)-privacy, exploring impression on reconstruction success. This second half will make use of TensorFlow Privateness, launched in a earlier weblog publish.

Half 1: Mannequin inversion in motion

Instance dataset: All of the world’s letters

The general technique of mannequin inversion used right here is the next. With no, or scarcely any, insider data a few mannequin, – however given alternatives to repeatedly question it –, I wish to learn to reconstruct unknown inputs primarily based on simply mannequin outputs . Independently of authentic mannequin coaching, this, too, is a coaching course of; nonetheless, on the whole it is not going to contain the unique information, as these gained’t be publicly out there. Nonetheless, for greatest success, the attacker mannequin is skilled with information as related as potential to the unique coaching information assumed. Pondering of pictures, for instance, and presupposing the favored view of successive layers representing successively coarse-grained options, we wish that the surrogate information to share as many illustration areas with the actual information as potential – as much as the very highest layers earlier than closing classification, ideally.

If we wished to make use of classical MNIST for example, one factor we might do is to solely use among the digits for coaching the “actual” mannequin; and the remainder, for coaching the adversary. Let’s strive one thing completely different although, one thing that may make the enterprise tougher in addition to simpler on the similar time. More durable, as a result of the dataset options exemplars extra advanced than MNIST digits; simpler due to the identical purpose: Extra might probably be discovered, by the adversary, from a fancy activity.

Initially designed to develop a machine mannequin of idea studying and generalization (Lake, Salakhutdinov, and Tenenbaum 2015), the OmniGlot dataset incorporates characters from fifty alphabets, cut up into two disjoint teams of thirty and twenty alphabets every. We’ll use the group of twenty to coach our goal mannequin. Here’s a pattern:


Sample from the twenty-alphabet set used to train the target model (originally: 'evaluation set')

Determine 1: Pattern from the twenty-alphabet set used to coach the goal mannequin (initially: ‘analysis set’)

The group of thirty we don’t use; as a substitute, we’ll make use of two small five-alphabet collections to coach the adversary and to check reconstruction, respectively. (These small subsets of the unique “huge” thirty-alphabet set are once more disjoint.)

Right here first is a pattern from the set used to coach the adversary.


Sample from the five-alphabet set used to train the adversary (originally: 'background small 1')

Determine 2: Pattern from the five-alphabet set used to coach the adversary (initially: ‘background small 1’)

The opposite small subset will likely be used to check the adversary’s spying capabilities after coaching. Let’s peek at this one, too:


Sample from the five-alphabet set used to test the adversary after training(originally: 'background small 2')

Determine 3: Pattern from the five-alphabet set used to check the adversary after coaching(initially: ‘background small 2’)

Conveniently, we will use tfds, the R wrapper to TensorFlow Datasets, to load these subsets:

Now first, we prepare the goal mannequin.

Prepare goal mannequin

The dataset initially has 4 columns: the picture, of dimension 105 x 105; an alphabet id and a within-dataset character id; and a label. For our use case, we’re probably not within the activity the goal mannequin was/is used for; we simply wish to get on the information. Principally, no matter activity we select, it’s not far more than a dummy activity. So, let’s simply say we prepare the goal to categorise characters by alphabet.

We thus throw out all unneeded options, holding simply the alphabet id and the picture itself:

# normalize and work with a single channel (pictures are black-and-white anyway)
preprocess_image <- perform(picture) {
  picture %>%
    tf$solid(dtype = tf$float32) %>%
    tf$truediv(y = 255) %>%
    tf$picture$rgb_to_grayscale()
}

# use the primary 11000 pictures for coaching
train_ds <- omni_train %>% 
  dataset_take(11000) %>%
  dataset_map(perform(file) {
    file$picture <- preprocess_image(file$picture)
    checklist(file$picture, file$alphabet)}) %>%
  dataset_shuffle(1000) %>% 
  dataset_batch(32)

# use the remaining 2180 data for validation
val_ds <- omni_train %>% 
  dataset_skip(11000) %>%
  dataset_map(perform(file) {
    file$picture <- preprocess_image(file$picture)
    checklist(file$picture, file$alphabet)}) %>%
  dataset_batch(32)

The mannequin consists of two components. The primary is imagined to run in a distributed trend; for instance, on cell units (stage one). These units then ship mannequin outputs to a central server, the place closing outcomes are computed (stage two). Positive, you can be pondering, this can be a handy setup for our situation: If we intercept stage one outcomes, we – most likely – achieve entry to richer data than what’s contained in a mannequin’s closing output layer. — That’s appropriate, however the situation is much less contrived than one would possibly assume. Identical to federated studying (McMahan et al. 2016), it fulfills vital desiderata: Precise coaching information by no means leaves the units, thus staying (in concept!) non-public; on the similar time, ingoing visitors to the server is considerably diminished.

In our instance setup, the on-device mannequin is a convnet, whereas the server mannequin is a straightforward feedforward community.

We hyperlink each collectively as a TargetModel that when referred to as usually, will run each steps in succession. Nevertheless, we’ll be capable of name target_model$mobile_step() individually, thereby intercepting intermediate outcomes.

on_device_model <- keras_model_sequential() %>%
  layer_conv_2d(filters = 32, kernel_size = c(7, 7),
                input_shape = c(105, 105, 1), activation = "relu") %>%
  layer_batch_normalization() %>%
  layer_max_pooling_2d(pool_size = c(3, 3), strides = 3) %>%
  layer_dropout(0.2) %>%
  layer_conv_2d(filters = 32, kernel_size = c(7, 7), activation = "relu") %>%
  layer_batch_normalization() %>%
  layer_max_pooling_2d(pool_size = c(3, 3), strides = 2) %>%
  layer_dropout(0.2) %>%
  layer_conv_2d(filters = 32, kernel_size = c(5, 5), activation = "relu") %>%
  layer_batch_normalization() %>%
  layer_max_pooling_2d(pool_size = c(2, 2), strides = 2) %>%
  layer_dropout(0.2) %>%
  layer_conv_2d(filters = 32, kernel_size = c(3, 3), activation = "relu") %>%
  layer_batch_normalization() %>%
  layer_max_pooling_2d(pool_size = c(2, 2), strides = 2) %>%
  layer_dropout(0.2) 

server_model <- keras_model_sequential() %>%
  layer_dense(models = 256, activation = "relu") %>%
  layer_flatten() %>%
  layer_dropout(0.2) %>% 
  # now we have simply 20 completely different ids, however they aren't in lexicographic order
  layer_dense(models = 50, activation = "softmax")

target_model <- perform() {
  keras_model_custom(title = "TargetModel", perform(self) {
    
    self$on_device_model <-on_device_model
    self$server_model <- server_model
    self$mobile_step <- perform(inputs) 
      self$on_device_model(inputs)
    self$server_step <- perform(inputs)
      self$server_model(inputs)

    perform(inputs, masks = NULL) {
      inputs %>% 
        self$mobile_step() %>%
        self$server_step()
    }
  })
  
}

mannequin <- target_model()

The general mannequin is a Keras customized mannequin, so we prepare it TensorFlow 2.x – type. After ten epochs, coaching and validation accuracy are at ~0.84 and ~0.73, respectively – not dangerous in any respect for a 20-class discrimination activity.

loss <- loss_sparse_categorical_crossentropy
optimizer <- optimizer_adam()

train_loss <- tf$keras$metrics$Imply(title='train_loss')
train_accuracy <-  tf$keras$metrics$SparseCategoricalAccuracy(title='train_accuracy')

val_loss <- tf$keras$metrics$Imply(title='val_loss')
val_accuracy <-  tf$keras$metrics$SparseCategoricalAccuracy(title='val_accuracy')

train_step <- perform(pictures, labels) {
  with (tf$GradientTape() %as% tape, {
    predictions <- mannequin(pictures)
    l <- loss(labels, predictions)
  })
  gradients <- tape$gradient(l, mannequin$trainable_variables)
  optimizer$apply_gradients(purrr::transpose(checklist(
    gradients, mannequin$trainable_variables
  )))
  train_loss(l)
  train_accuracy(labels, predictions)
}

val_step <- perform(pictures, labels) {
  predictions <- mannequin(pictures)
  l <- loss(labels, predictions)
  val_loss(l)
  val_accuracy(labels, predictions)
}


training_loop <- tf_function(autograph(perform(train_ds, val_ds) {
  for (b1 in train_ds) {
    train_step(b1[[1]], b1[[2]])
  }
  for (b2 in val_ds) {
    val_step(b2[[1]], b2[[2]])
  }
  
  tf$print("Prepare accuracy", train_accuracy$consequence(),
           "    Validation Accuracy", val_accuracy$consequence())
  
  train_loss$reset_states()
  train_accuracy$reset_states()
  val_loss$reset_states()
  val_accuracy$reset_states()
}))


for (epoch in 1:10) {
  cat("Epoch: ", epoch, " -----------n")
  training_loop(train_ds, val_ds)  
}
Epoch:  1  -----------
Prepare accuracy 0.195090905     Validation Accuracy 0.376605511
Epoch:  2  -----------
Prepare accuracy 0.472272724     Validation Accuracy 0.5243119
...
...
Epoch:  9  -----------
Prepare accuracy 0.821454525     Validation Accuracy 0.720183492
Epoch:  10  -----------
Prepare accuracy 0.840454519     Validation Accuracy 0.726605475

Now, we prepare the adversary.

Prepare adversary

The adversary’s basic technique will likely be:

  • Feed its small, surrogate dataset to the on-device mannequin. The output acquired may be thought to be a (extremely) compressed model of the unique pictures.
  • Pass that “compressed” model as enter to its personal mannequin, which tries to reconstruct the unique pictures from the sparse code.
  • Evaluate authentic pictures (these from the surrogate dataset) to the reconstruction pixel-wise. The purpose is to attenuate the imply (squared, say) error.

Doesn’t this sound rather a lot just like the decoding facet of an autoencoder? No surprise the attacker mannequin is a deconvolutional community. Its enter – equivalently, the on-device mannequin’s output – is of dimension batch_size x 1 x 1 x 32. That’s, the data is encoded in 32 channels, however the spatial decision is 1. Identical to in an autoencoder working on pictures, we have to upsample till we arrive on the authentic decision of 105 x 105.

That is precisely what’s occurring within the attacker mannequin:

attack_model <- perform() {
  
  keras_model_custom(title = "AttackModel", perform(self) {
    
    self$conv1 <-layer_conv_2d_transpose(filters = 32, kernel_size = 9,
                                         padding = "legitimate",
                                         strides = 1, activation = "relu")
    self$conv2 <- layer_conv_2d_transpose(filters = 32, kernel_size = 7,
                                          padding = "legitimate",
                                          strides = 2, activation = "relu") 
    self$conv3 <- layer_conv_2d_transpose(filters = 1, kernel_size = 7,
                                          padding = "legitimate",
                                          strides = 2, activation = "relu")  
    self$conv4 <- layer_conv_2d_transpose(filters = 1, kernel_size = 5,
                                          padding = "legitimate",
                                          strides = 2, activation = "relu")
    
    perform(inputs, masks = NULL) {
      inputs %>% 
        # bs * 9 * 9 * 32
        # output = strides * (enter - 1) + kernel_size - 2 * padding
        self$conv1() %>%
        # bs * 23 * 23 * 32
        self$conv2() %>%
        # bs * 51 * 51 * 1
        self$conv3() %>%
        # bs * 105 * 105 * 1
        self$conv4()
    }
  })
  
}

attacker = attack_model()

To coach the adversary, we use one of many small (five-alphabet) subsets. To reiterate what was stated above, there isn’t a overlap with the info used to coach the goal mannequin.

attacker_ds <- omni_spy %>% 
dataset_map(perform(file) {
    file$picture <- preprocess_image(file$picture)
    checklist(file$picture, file$alphabet)}) %>%
  dataset_batch(32)

Right here, then, is the attacker coaching loop, striving to refine the decoding course of over 100 – quick – epochs:

attacker_criterion <- loss_mean_squared_error
attacker_optimizer <- optimizer_adam()
attacker_loss <- tf$keras$metrics$Imply(title='attacker_loss')
attacker_mse <-  tf$keras$metrics$MeanSquaredError(title='attacker_mse')

attacker_step <- perform(pictures) {
  
  attack_input <- mannequin$mobile_step(pictures)
  
  with (tf$GradientTape() %as% tape, {
    generated <- attacker(attack_input)
    l <- attacker_criterion(pictures, generated)
  })
  gradients <- tape$gradient(l, attacker$trainable_variables)
  attacker_optimizer$apply_gradients(purrr::transpose(checklist(
    gradients, attacker$trainable_variables
  )))
  attacker_loss(l)
  attacker_mse(pictures, generated)
}


attacker_training_loop <- tf_function(autograph(perform(attacker_ds) {
  for (b in attacker_ds) {
    attacker_step(b[[1]])
  }
  
  tf$print("mse: ", attacker_mse$consequence())
  
  attacker_loss$reset_states()
  attacker_mse$reset_states()
}))

for (epoch in 1:100) {
  cat("Epoch: ", epoch, " -----------n")
  attacker_training_loop(attacker_ds)  
}
Epoch:  1  -----------
  mse:  0.530902684
Epoch:  2  -----------
  mse:  0.201351956
...
...
Epoch:  99  -----------
  mse:  0.0413453057
Epoch:  100  -----------
  mse:  0.0413028933

The query now could be, – does it work? Has the attacker actually discovered to deduce precise information from (stage one) mannequin output?

Check adversary

To check the adversary, we use the third dataset we downloaded, containing pictures from 5 yet-unseen alphabets. For show, we choose simply the primary sixteen data – a very arbitrary determination, after all.

test_ds <- omni_test %>% 
  dataset_map(perform(file) {
    file$picture <- preprocess_image(file$picture)
    checklist(file$picture, file$alphabet)}) %>%
  dataset_take(16) %>%
  dataset_batch(16)

batch <- as_iterator(test_ds) %>% iterator_get_next()
pictures <- batch[[1]]

attack_input <- mannequin$mobile_step(pictures)
generated <- attacker(attack_input) %>% as.array()

generated[generated > 1] <- 1
generated <- generated[ , , , 1]
generated %>%
  purrr::array_tree(1) %>%
  purrr::map(as.raster) %>%
  purrr::iwalk(~{plot(.x)})

Identical to throughout the coaching course of, the adversary queries the goal mannequin (stage one), obtains the compressed illustration, and makes an attempt to reconstruct the unique picture. (After all, in the actual world, the setup could be completely different in that the attacker would not be capable of merely examine the photographs, as is the case right here. There would thus should be some option to intercept, and make sense of, community visitors.)

attack_input <- mannequin$mobile_step(pictures)
generated <- attacker(attack_input) %>% as.array()

generated[generated > 1] <- 1
generated <- generated[ , , , 1]
generated %>%
  purrr::array_tree(1) %>%
  purrr::map(as.raster) %>%
  purrr::iwalk(~{plot(.x)})

To permit for simpler comparability (and improve suspense …!), right here once more are the precise pictures, which we displayed already when introducing the dataset:


First images from the test set, the way they really look.

Determine 4: First pictures from the check set, the best way they actually look.

And right here is the reconstruction:


First images from the test set, as reconstructed by the adversary.

Determine 5: First pictures from the check set, as reconstructed by the adversary.

After all, it’s exhausting to say how revealing these “guesses” are. There undoubtedly appears to be a connection to character complexity; total, it looks like the Greek and Roman letters, that are the least advanced, are additionally those most simply reconstructed. Nonetheless, ultimately, how a lot privateness is misplaced will very a lot depend upon contextual elements.

In the beginning, do the exemplars within the dataset signify people or courses of people? If – as in actuality – the character X represents a category, it may not be so grave if we have been in a position to reconstruct “some X” right here: There are numerous Xs within the dataset, all fairly related to one another; we’re unlikely to precisely to have reconstructed one particular, particular person X. If, nonetheless, this was a dataset of particular person individuals, with all Xs being pictures of Alex, then in reconstructing an X now we have successfully reconstructed Alex.

Second, in much less apparent eventualities, evaluating the diploma of privateness breach will possible surpass computation of quantitative metrics, and contain the judgment of area consultants.

Talking of quantitative metrics although – our instance looks like an ideal use case to experiment with differential privateness. Differential privateness is measured by (epsilon) (decrease is best), the primary thought being that solutions to queries to a system ought to rely as little as potential on the presence or absence of a single (any single) datapoint.

So, we’ll repeat the above experiment, utilizing TensorFlow Privateness (TFP) so as to add noise, in addition to clip gradients, throughout optimization of the goal mannequin. We’ll strive three completely different circumstances, leading to three completely different values for (epsilon)s, and for every situation, examine the photographs reconstructed by the adversary.

Half 2: Differential privateness to the rescue

Sadly, the setup for this a part of the experiment requires a bit workaround. Making use of the pliability afforded by TensorFlow 2.x, our goal mannequin has been a customized mannequin, becoming a member of two distinct levels (“cell” and “server”) that could possibly be referred to as independently.

TFP, nonetheless, does nonetheless not work with TensorFlow 2.x, that means now we have to make use of old-style, non-eager mannequin definitions and coaching. Fortunately, the workaround will likely be simple.

First, load (and probably, set up) libraries, taking care to disable TensorFlow V2 habits.

The coaching set is loaded, preprocessed and batched (practically) as earlier than.

omni_train <- tfds$load("omniglot", cut up = "check")

batch_size <- 32

train_ds <- omni_train %>%
  dataset_take(11000) %>%
  dataset_map(perform(file) {
    file$picture <- preprocess_image(file$picture)
    checklist(file$picture, file$alphabet)}) %>%
  dataset_shuffle(1000) %>%
  # want dataset_repeat() when not keen
  dataset_repeat() %>%
  dataset_batch(batch_size)

Prepare goal mannequin – with TensorFlow Privateness

To coach the goal, we put the layers from each levels – “cell” and “server” – into one sequential mannequin. Observe how we take away the dropout. It is because noise will likely be added throughout optimization anyway.

complete_model <- keras_model_sequential() %>%
  layer_conv_2d(filters = 32, kernel_size = c(7, 7),
                input_shape = c(105, 105, 1),
                activation = "relu") %>%
  layer_batch_normalization() %>%
  layer_max_pooling_2d(pool_size = c(3, 3), strides = 3) %>%
  #layer_dropout(0.2) %>%
  layer_conv_2d(filters = 32, kernel_size = c(7, 7), activation = "relu") %>%
  layer_batch_normalization() %>%
  layer_max_pooling_2d(pool_size = c(3, 3), strides = 2) %>%
  #layer_dropout(0.2) %>%
  layer_conv_2d(filters = 32, kernel_size = c(5, 5), activation = "relu") %>%
  layer_batch_normalization() %>%
  layer_max_pooling_2d(pool_size = c(2, 2), strides = 2) %>%
  #layer_dropout(0.2) %>%
  layer_conv_2d(filters = 32, kernel_size = c(3, 3), activation = "relu") %>%
  layer_batch_normalization() %>%
  layer_max_pooling_2d(pool_size = c(2, 2), strides = 2, title = "mobile_output") %>%
  #layer_dropout(0.2) %>%
  layer_dense(models = 256, activation = "relu") %>%
  layer_flatten() %>%
  #layer_dropout(0.2) %>%
  layer_dense(models = 50, activation = "softmax")

Utilizing TFP primarily means utilizing a TFP optimizer, one which clips gradients in keeping with some outlined magnitude and provides noise of outlined dimension. noise_multiplier is the parameter we’re going to differ to reach at completely different (epsilon)s:

l2_norm_clip <- 1

# ratio of the usual deviation to the clipping norm
# we run coaching for every of the three values
noise_multiplier <- 0.7
noise_multiplier <- 0.5
noise_multiplier <- 0.3

# similar as batch dimension
num_microbatches <- k_cast(batch_size, "int32")
learning_rate <- 0.005

optimizer <- tfp$DPAdamGaussianOptimizer(
  l2_norm_clip = l2_norm_clip,
  noise_multiplier = noise_multiplier,
  num_microbatches = num_microbatches,
  learning_rate = learning_rate
)

In coaching the mannequin, the second vital change for TFP we have to make is to have loss and gradients computed on the person stage.

# want so as to add noise to each particular person contribution
loss <- tf$keras$losses$SparseCategoricalCrossentropy(discount =   tf$keras$losses$Discount$NONE)

complete_model %>% compile(loss = loss, optimizer = optimizer, metrics = "sparse_categorical_accuracy")

num_epochs <- 20

n_train <- 13180

historical past <- complete_model %>% match(
  train_ds,
  # want steps_per_epoch when not in keen mode
  steps_per_epoch = n_train/batch_size,
  epochs = num_epochs)

To check three completely different (epsilon)s, we run this thrice, every time with a special noise_multiplier. Every time we arrive at a special closing accuracy.

Here’s a synopsis, the place (epsilon) was computed like so:

compute_priv <- tfp$privateness$evaluation$compute_dp_sgd_privacy

compute_priv$compute_dp_sgd_privacy(
  # variety of data in coaching set
  n_train,
  batch_size,
  # noise_multiplier
  0.7, # or 0.5, or 0.3
  # variety of epochs
  20,
  # delta - mustn't exceed 1/variety of examples in coaching set
  1e-5)
0.7 4.0 0.37
0.5 12.5 0.45
0.3 84.7 0.56

Now, because the adversary gained’t name the whole mannequin, we have to “reduce off” the second-stage layers. This leaves us with a mannequin that executes stage-one logic solely. We save its weights, so we will later name it from the adversary:

intercepted <- keras_model(
  complete_model$enter,
  complete_model$get_layer("mobile_output")$output
)

intercepted %>% save_model_hdf5("./intercepted.hdf5")

Prepare adversary (towards differentially non-public goal)

In coaching the adversary, we will preserve a lot of the authentic code – that means, we’re again to TF-2 type. Even the definition of the goal mannequin is identical as earlier than:

https://doi.org/10.1007/11681878_14.

Fredrikson, Matthew, Eric Lantz, Somesh Jha, Simon Lin, David Web page, and Thomas Ristenpart. 2014. “Privateness in Pharmacogenetics: An Finish-to-Finish Case Research of Personalised Warfarin Dosing.” In Proceedings of the twenty third USENIX Convention on Safety Symposium, 17–32. SEC’14. USA: USENIX Affiliation.

Lake, Brenden M., Ruslan Salakhutdinov, and Joshua B. Tenenbaum. 2015. “Human-Stage Idea Studying By Probabilistic Program Induction.” Science 350 (6266): 1332–38. https://doi.org/10.1126/science.aab3050.
McMahan, H. Brendan, Eider Moore, Daniel Ramage, and Blaise Agüera y Arcas. 2016. “Federated Studying of Deep Networks Utilizing Mannequin Averaging.” CoRR abs/1602.05629. http://arxiv.org/abs/1602.05629.

Wu, X., M. Fredrikson, S. Jha, and J. F. Naughton. 2016. “A Methodology for Formalizing Mannequin-Inversion Assaults.” In 2016 IEEE twenty ninth Laptop Safety Foundations Symposium (CSF), 355–70.

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