Watch · narrated walkthroughs
FIPS 205 is often summarised as the signature that rests on hashing alone. This paper series reads what that sentence leaves out: why every hash call is tweaked with an address and a public seed and what the repaired security proof actually assumes, how security slides as one key signs past its two-to-the-sixty-four budget, why the SHA-2 instantiation needed SHA-512 at the higher categories, how a single induced fault can graft a forged tree onto a genuine key, and how to choose and budget a hash-based root in 2026 now that NIST has drafted limited-use parameter sets and CNSA 2.0 has picked stateful schemes. Every topic is tied to the keys AI agents depend on: model-release roots, tool and plug-in signing, and long-lived firmware anchors.