IETF RFC 9958 explains post-quantum cryptography for engineers
18 JUNE 2026, GLOBAL
The Internet Engineering Task Force published RFC 9958, "Post-Quantum Cryptography for Engineers," on 18 June 2026. The document explains post-quantum cryptography for the engineers who must implement it, and its central message is blunt: migrating may require redesigning protocols, not simply swapping one algorithm for another.
The reason lies in how post-quantum algorithms differ. They often have larger keys and signatures than the algorithms they replace, which can break assumptions that existing protocols build in, such as the size of a field or a packet. Fitting the new algorithms in sometimes means changing how a protocol works, so engineers cannot always treat migration as a drop-in replacement.
That distinction is why the RFC exists. Engineers and architects implementing post-quantum cryptography need to understand the practical implications beyond choosing an algorithm. By spelling out where protocol-level work is required, the RFC helps teams plan for it in advance rather than discovering mid-migration that a protocol cannot carry the new cryptography unchanged.
Why it matters. RFC 9958 corrects a common misconception that post-quantum migration is just an algorithm swap. Because post-quantum algorithms can force protocol redesign, teams that plan only for a drop-in replacement may hit surprises. Engineers can use the RFC to identify where their protocols need redesign and budget for that work, which makes crypto agility at the protocol level as valuable as agility at the algorithm level.