Glossary
Crypto Agility
Crypto agility is a system's ability to swap out the underlying cryptographic algorithms it uses — for signing, encryption, key exchange — without requiring a fundamental redesign of the system around them. A system built with this in mind treats the specific algorithm as a configurable, replaceable component; one built without it hardcodes assumptions about a particular algorithm throughout, which turns any future algorithm change into a project closer to a rewrite than a swap.
This property is what determines whether a post-quantum migration is a manageable, incremental undertaking or an enormous one. A crypto-agile system can adopt new algorithms as they mature and become standardized, well ahead of any actual quantum threat becoming practical; a system without this flexibility has to defer the question until it becomes urgent, at which point the work is both harder and more time-pressured than it would have been if planned for in advance.