Optimizing OpenSSL's AES-CFB128 with Vector AES: Performance Gains and Hard-Won Lessons

Cryptographic implementations demand both correctness and security but how do you optimize an algorithm like AES-CFB128 for modern CPUs? This case study explores the evolution of OpenSSL’s AES-CFB128 implementation, from a sequential AES-NI baseline to a high-performance VAES-optimized version (openssl#26902). We’ll deep dive into: - SIMD and compiler optimization techniques, - performance measurement and characterization, - tooling and debugging challenges, - security considerations, - lessons learned as an external contributor