On page 21 of the Rivest's Cryptology chapter, he defines a trapdoor predicate as a boolean function for which it is easy to choose an
x such that
B(x) = v, but hard for an adversary to compute
x, without the trapdoor information.
He goes on to say that Alice's public key contains a description of B.
What exactly goes into this description, to enable the trapdoor predicate property, without giving away the secret key?