Mosca's theorem
A planning rule stating that you have a problem if the time your data must stay secret, plus the time your migration takes, exceeds the time until a cryptographically relevant quantum computer arrives.
In practice
Ten-year confidentiality plus a five-year migration means a fifteen-year horizon — so a CRQC in 2035 is already a live constraint.
Related terms
The practice of recording encrypted traffic today in order to decrypt it once a quantum computer becomes available. It is the one quantum risk already in progress, and it makes long-life confidential data the first migration priority.
Informal shorthand for the day a cryptographically relevant quantum computer becomes available. It is a planning device rather than a forecast — the useful question is whether your migration finishes before it, not when it lands.
A structured record of every algorithm, key, certificate, protocol, library and vendor dependency in an organisation. It is the mandatory first step of a post-quantum migration, because you cannot replace what you cannot enumerate.