The phrase "a key which" is correct and usable in written English.
It can be used when referring to a specific key that serves a particular function or purpose.
Example: "The software requires a key which unlocks additional features for premium users."
Alternatives: "a key that" or "a key enabling".
Now the only way to open them is with a key, which she has, and I don't.
I have a sense that all my pieces have a key, which doesn't mean I can identify it".
The valuable item, of course, was a KEY, which was found at the intersection of KEYBOARDS (51A) and JOCKEY (35D).
Residential students can also stop by the Facilities Management Office in Holmes Hall 4 to temporarily check out a key, which they will need to return immediately after getting into their room and retrieving their own keys.
A year later, rummaging through Thomas's things, Oskar finds an envelope containing a key, which he assumes will unlock a box or something that will reveal a new aspect of his father to him.
Though the higher military authorities lost faith in them (with some going so far as to urge their abandonment), more-discerning eyes realized that here was a key which, when properly used, would unlock the trench barrier.
A public key is derived from a private key, which is created by using a digital signature algorithm.
"The drug is a skeleton key which unlocks an interior door to places we don't generally have access to," Dr Richards said.
Adopting a pedal key, which would take a pounding from the organist's feet, was the least expensive: Only $25.
A key homomorphic encryption [10, 39] is used to provide protection from a cached key, which is explained further in a later section.
All Stanford Earth vehicles have a spare key, which should be given to a responsible party during the trip.
