authenticate

v. confirm, verify; show to be authentic; prove that a document is authentic and not a forgery

Authentication (from Greek αυθεντικός; real or genuine, from authentes; author) is the act of establishing or confirming something (or someone) as authentic, that is, that claims made by or about the thing are true. Authenticating an object may mean confirming its provenance, whereas authenticating a person often consists of verifying their identity. Authentication depends upon one or more authentication factors.
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Verb
1. establish the authenticity of something
(hypernym) attest, certify, manifest, demonstrate, evidence
(hyponym) prove
(entail) verify
(derivation) authentication, hallmark, assay-mark

(v. t.)
To render authentic; to give authority to, by the proof, attestation, or formalities required by law, or sufficient to entitle to credit.
  

(v. t.)
To prove authentic; to determine as real and true; as, to authenticate a portrait.
  

1. To establish, usually by challenge and response, that a transmission attempt is authorized and valid. 2. Verify the identity of a user, user device, or other entity, or the integrity of data stored, transmitted, or otherwise exposed to unauthorized modification in an automated information system, or establish the validity of a transmitted message. [NIS] 3. A challenge given by voice or electrical means to attest to the authenticity of a message or transmission. [JP1]