certifying

(transitive) To attest to (a fact) as the truth.
(transitive) To authenticate or verify in writing.
(transitive) To attest that a product, service, organization, or person has met an official standard.
(archaic, transitive) To inform; to tell (a person) that something is true.
(archaic, reflexive) To assure (oneself) of something; to ascertain.