Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

[EX Q]: in cryptography, a pre-shared key or psk is a shared secret which was previously shared between the two parties using some secure channel before it is used.
[EX A]: pre-shared key

[EX Q]: in law, a conviction is the verdict that results when a court of law finds a defendant guilty of a crime.
[EX A]: conviction

[EX Q]: sarbhana is one of the 51 union councils of abbottabad district in the khyber pakhtunkhwa province of pakistan.
[EX A]:
sarbhana