keras_example

Keras Example

This directory contains code examples using attacking method with Keras platform (Tensorflow as backend, of course). A couple of things to tweak before using Keras with Tensorflow tensors. You could refer to the official document on Keras+Tensorflow.

Essentially, we need to notify Keras that we want to manage the session ourselves.

import tensorflow as tf
from keras import backend as K

sess = tf.Session()
# sess = tf.InteractiveSession()
K.set_session(sess)

The model is defined using the Keras syntax.

model = Sequential([
    Conv2D(filters=32, kernel_size=(3, 3), padding='same',
           input_shape=input_shape),
    MaxPooling2D(pool_size=(2, 2), padding='same'),
    Flatten(),
    Dense(10),
    Activation('softmax')])

model.compile(optimizer='adam', loss='categorical_crossentropy',
              metrics=['accuracy'])

And the adversarial crafting graph is created via

x = tf.placeholder(tf.float32, (None, img_rows, img_cols, img_chas))

def _model_fn(x, logits=False):
    ybar = model(x)
    logits_, = ybar.op.inputs
    if logits:
        return ybar, logits_
    return ybar

x_adv = fgsm(_model_fn, x, epochs=9, eps=0.02)

And the _model_fn needs to have the signature that

1. The first parameter must be the network input variable, usually a tf.placeholder.
2. The second parameter must be the logits, with default value False. if True, return the output tensor and the logits. Otherwise, return the output tensor only. The rational is that we use tf.nn.softmax_cross_entropy_with_logits in the attacking method to calculate the loss.
3. You may pass other parameters to your function provided that they all have default values.

Bug

Currently there is a bug keras/issues/5469 when using Dropout layer in Keras with Tensorflow as backend. If Dropout is used, then The number of epochs for tf.while_loop cannot exceed 10 (the default value of parallel_iterations, I do not know why…), otherwise the program will hang. Refer to the bug report for more information.

To workaround the bug, all Dropout layers are commented out. I tried pure code with Tensorflow and it works fine, so it should be the Keras internal implementation problem.