Sub-Second Proof-of-Work: Winning the $51k KernelCTF with AVX-512

In May 2025, the Crusaders of Rust team discovered and exploited a use-after-free bug in Linux's packet scheduler, aiming for Google's kernelCTF's $51,000 bounty. The author details their crucial contribution: optimizing the competition's proof-of-work (a Verifiable Delay Function, or VDF) using AVX-512IFMA instructions. Through mathematical optimizations, C++ porting, and meticulous assembly-level tweaks, they slashed execution time from 1.4 seconds to a blistering 0.21 seconds, ultimately securing the team's victory with a record-breaking 3.6-second submission. This showcases a deep understanding of low-level hardware and a relentless pursuit of performance.