  There has been extensive research on developing defense techniques against
adversarial attacks; however, they have been mainly designed for specific model
families or application domains, therefore, they cannot be easily extended.
Based on the design philosophy of ensemble of diverse weak defenses, we propose
ATHENA---a flexible and extensible framework for building generic yet effective
defenses against adversarial attacks. We have conducted a comprehensive
empirical study to evaluate several realizations of ATHENA with four threat
models including zero-knowledge, black-box, gray-box, and white-box. We also
explain (i) why diversity matters, (ii) the generality of the defense
framework, and (iii) the overhead costs incurred by ATHENA.
