Updates for Boundary Attack

[beat-buesser]

Signed-off-by: Beat Buesser beat.buesser@ie.ibm.com

Description

This pull request provides updates for BoundaryAttack to make it consistent with the reference implementation and support all input shapes. The updated BoundaryAttack calculates perturbation and direction on the entire input instead of per channel and applies the correct inner product calculation resulting in faster convergence.

Thank you to Michael Craig and Manish Bhardwaj for sharing this update.

Type of change

Please check all relevant options.

• Improvement (non-breaking)
• Bug fix (non-breaking)
• New feature (non-breaking)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[minhitbk]

@beat-buesser The code looks good, I just have a few minor suggestions.