Function request_key 

pub fn request_key(verifier_root: Word, claim_commitment: Word) -> Word

Returns the advice-map key addressing a proof package for claim_commitment under the verifier identified by verifier_root.

The key is H_tag(claim_commitment ‖ verifier_root) (one rate block, domain-separated). It is a lookup address, not a trust anchor: the verifier re-checks the retrieved package against the claim, so a wrong package fails verification. Both inputs are values the requester owns (the verifier’s MAST root; the claim commitment it computed or holds from its own inputs) — neither is taken from advice.