encountering, by a media player of a media presentation system, a trigger to transmit an advertisement request to a computing device associated with a media provider;

responsive to encountering the trigger to transmit the advertisement request and before a transmission of the advertisement request to the computing device, generating, by the media player, an attestation watermark indicative of an authenticity of the media player using a cryptographic key, wherein the cryptographic key is stored by the media player, and wherein generating the attestation watermark comprises: (i) generating a data object specifying a claim related to the media player, wherein the specified claim comprises a timestamp indicative of an expiration time of the attestation watermark; and (ii) cryptographically signing the data object using the cryptographic key, and wherein the specified claim comprises a device identifier of the media player;

attaching, by the media player, the attestation watermark to the advertisement request; and

based on encountering the trigger, transmitting, by the media player, the advertisement request having the attached attestation watermark to the computing device, wherein the authenticity of the media player is verifiable by the computing device using the attestation watermark.