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# Copyright 2019, The TensorFlow Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Training a CNN on MNIST with vectorized DP-SGD optimizer."""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from absl import app
from absl import flags
from distutils.version import LooseVersion
import numpy as np
import tensorflow as tf
from privacy.analysis.rdp_accountant import compute_rdp
from privacy.analysis.rdp_accountant import get_privacy_spent
from privacy.optimizers import dp_optimizer_vectorized
flags.DEFINE_boolean(
'dpsgd', True, 'If True, train with DP-SGD. If False, '
'train with vanilla SGD.')
flags.DEFINE_float('learning_rate', .15, 'Learning rate for training')
flags.DEFINE_float('noise_multiplier', 1.1,
'Ratio of the standard deviation to the clipping norm')
flags.DEFINE_float('l2_norm_clip', 1.0, 'Clipping norm')
flags.DEFINE_integer('batch_size', 200, 'Batch size')
flags.DEFINE_integer('epochs', 60, 'Number of epochs')
flags.DEFINE_integer(
'microbatches', 200, 'Number of microbatches '
'(must evenly divide batch_size)')
flags.DEFINE_string('model_dir', None, 'Model directory')
FLAGS = flags.FLAGS
NUM_TRAIN_EXAMPLES = 60000
if LooseVersion(tf.__version__) < LooseVersion('2.0.0'):
GradientDescentOptimizer = tf.train.GradientDescentOptimizer
else:
GradientDescentOptimizer = tf.optimizers.SGD # pylint: disable=invalid-name
def compute_epsilon(steps):
"""Computes epsilon value for given hyperparameters."""
if FLAGS.noise_multiplier == 0.0:
return float('inf')
orders = [1 + x / 10. for x in range(1, 100)] + list(range(12, 64))
sampling_probability = FLAGS.batch_size / NUM_TRAIN_EXAMPLES
rdp = compute_rdp(q=sampling_probability,
noise_multiplier=FLAGS.noise_multiplier,
steps=steps,
orders=orders)
# Delta is set to approximate 1 / (number of training points).
return get_privacy_spent(orders, rdp, target_delta=1e-5)[0]
def cnn_model_fn(features, labels, mode):
"""Model function for a CNN."""
# Define CNN architecture using tf.keras.layers.
input_layer = tf.reshape(features['x'], [-1, 28, 28, 1])
y = tf.keras.layers.Conv2D(16, 8,
strides=2,
padding='same',
activation='relu').apply(input_layer)
y = tf.keras.layers.MaxPool2D(2, 1).apply(y)
y = tf.keras.layers.Conv2D(32, 4,
strides=2,
padding='valid',
activation='relu').apply(y)
y = tf.keras.layers.MaxPool2D(2, 1).apply(y)
y = tf.keras.layers.Flatten().apply(y)
y = tf.keras.layers.Dense(32, activation='relu').apply(y)
logits = tf.keras.layers.Dense(10).apply(y)
# Calculate loss as a vector (to support microbatches in DP-SGD).
vector_loss = tf.nn.sparse_softmax_cross_entropy_with_logits(
labels=labels, logits=logits)
# Define mean of loss across minibatch (for reporting through tf.Estimator).
scalar_loss = tf.reduce_mean(vector_loss)
# Configure the training op (for TRAIN mode).
if mode == tf.estimator.ModeKeys.TRAIN:
if FLAGS.dpsgd:
# Use DP version of GradientDescentOptimizer. Other optimizers are
# available in dp_optimizer. Most optimizers inheriting from
# tf.train.Optimizer should be wrappable in differentially private
# counterparts by calling dp_optimizer.optimizer_from_args().
optimizer = dp_optimizer_vectorized.VectorizedDPSGD(
l2_norm_clip=FLAGS.l2_norm_clip,
noise_multiplier=FLAGS.noise_multiplier,
num_microbatches=FLAGS.microbatches,
learning_rate=FLAGS.learning_rate)
opt_loss = vector_loss
else:
optimizer = GradientDescentOptimizer(learning_rate=FLAGS.learning_rate)
opt_loss = scalar_loss
global_step = tf.train.get_global_step()
train_op = optimizer.minimize(loss=opt_loss, global_step=global_step)
# In the following, we pass the mean of the loss (scalar_loss) rather than
# the vector_loss because tf.estimator requires a scalar loss. This is only
# used for evaluation and debugging by tf.estimator. The actual loss being
# minimized is opt_loss defined above and passed to optimizer.minimize().
return tf.estimator.EstimatorSpec(mode=mode,
loss=scalar_loss,
train_op=train_op)
# Add evaluation metrics (for EVAL mode).
elif mode == tf.estimator.ModeKeys.EVAL:
eval_metric_ops = {
'accuracy':
tf.metrics.accuracy(
labels=labels,
predictions=tf.argmax(input=logits, axis=1))
}
return tf.estimator.EstimatorSpec(mode=mode,
loss=scalar_loss,
eval_metric_ops=eval_metric_ops)
def load_mnist():
"""Loads MNIST and preprocesses to combine training and validation data."""
train, test = tf.keras.datasets.mnist.load_data()
train_data, train_labels = train
test_data, test_labels = test
train_data = np.array(train_data, dtype=np.float32) / 255
test_data = np.array(test_data, dtype=np.float32) / 255
train_labels = np.array(train_labels, dtype=np.int32)
test_labels = np.array(test_labels, dtype=np.int32)
assert train_data.min() == 0.
assert train_data.max() == 1.
assert test_data.min() == 0.
assert test_data.max() == 1.
assert train_labels.ndim == 1
assert test_labels.ndim == 1
return train_data, train_labels, test_data, test_labels
def main(unused_argv):
tf.logging.set_verbosity(tf.logging.INFO)
if FLAGS.dpsgd and FLAGS.batch_size % FLAGS.microbatches != 0:
raise ValueError('Number of microbatches should divide evenly batch_size')
# Load training and test data.
train_data, train_labels, test_data, test_labels = load_mnist()
# Instantiate the tf.Estimator.
mnist_classifier = tf.estimator.Estimator(model_fn=cnn_model_fn,
model_dir=FLAGS.model_dir)
# Create tf.Estimator input functions for the training and test data.
train_input_fn = tf.estimator.inputs.numpy_input_fn(
x={'x': train_data},
y=train_labels,
batch_size=FLAGS.batch_size,
num_epochs=FLAGS.epochs,
shuffle=True)
eval_input_fn = tf.estimator.inputs.numpy_input_fn(
x={'x': test_data},
y=test_labels,
num_epochs=1,
shuffle=False)
# Training loop.
steps_per_epoch = NUM_TRAIN_EXAMPLES // FLAGS.batch_size
for epoch in range(1, FLAGS.epochs + 1):
# Train the model for one epoch.
mnist_classifier.train(input_fn=train_input_fn, steps=steps_per_epoch)
# Evaluate the model and print results
eval_results = mnist_classifier.evaluate(input_fn=eval_input_fn)
test_accuracy = eval_results['accuracy']
print('Test accuracy after %d epochs is: %.3f' % (epoch, test_accuracy))
# Compute the privacy budget expended.
if FLAGS.dpsgd:
eps = compute_epsilon(epoch * NUM_TRAIN_EXAMPLES // FLAGS.batch_size)
print('For delta=1e-5, the current epsilon is: %.2f' % eps)
else:
print('Trained with vanilla non-private SGD optimizer')
if __name__ == '__main__':
app.run(main)
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