Jumpkeys are small metal cylinders that contain the information for making jumps through jumpgates. They have markings denoting their target routes. The key holds a code that when transmitted to a jumpgate opens a portal. Not all ships in a fleet need a key, as long as they have jump engines (a secret tech of The Supreme Order of Engineers).
The Charioteers hold the knowledge of how to program new keys, and protects their monopoly fiercely. Charioteer security is always looking out for black market coders. It is possible to store a key on other computers, although this is rarely the practice among Charioteers who see it as an infringement on their monopoly.
Although the Charioteers hold the monopoly on new keys, there are enough inherited relic keys around to keep noble and Church fleets moving. Keys are a highly valued price for pirates and navies after a battle.