Jan Janasek

— On the schedule —

Going beyond constant-time security in open-source cryptographic libraries

Most open-source cryptographic libraries now use constant-time execution to thwart timing attacks. However, this baseline remains vulnerable to physical threats, such as power/Electromagnetic (EM) side channels and fault injection. In this short talk, we focus on the software engineering process needed to go beyond basic constant-time security. We present a systematic approach to integrating physical-attack defenses into existing open-source codebases, using BearSSL and its RSA implementation as our main case study; we also comment on similar challenges encountered during implementing ECC protections. Instead of proposing isolated mathematical changes, we show how to build a layered defensive architecture. The added security introduces an execution overhead of about 56% compared to the standard constant-time version, a practical trade-off for developers. We further outline a rigorous testing pipeline: a ChipWhisperer platform to test for side-channel leaks on the Cortex-M4 architecture, and a software simulator for fault-injection testing. This way we demonstrate that engineering physical-attack protections is practical even for real-world open-source deployments.