1. A computer-implemented method comprising: characterizing multiple items of content accessed over a network, each item of content associated with a content descriptor and characterized with a set of multiple depersonalized keywords, the set comprising words submitted to an online search engine by a population comprising multiple entities in the past to locate the content; recording, at a keyword mapping system, a consumption history of a specified entity, the consumption history comprising at least two different content descriptors, each content descriptor associated with a respective item of content accessed over the network by the specified entity; selecting, from the recorded consumption history, at least two content descriptors which have been stored for longer than a specified timeframe; converting the recorded consumption history to a protected consumption history by representing each selected content descriptor with the set of multiple depersonalized keywords which characterize the respective selected content descriptor's item of content; removing the selected content descriptors from the protected consumption history; receiving a bid request from an advertising exchange, the bid request comprising an identifier of the specified entity; determining a frequency of each specified keyword from a list of specified keywords in the depersonalized keywords of the protected consumption history; configuring a bid response by assessing the suitability of the specified entity to receive advertising content based at least in part on the frequencies; and sending the bid response to the advertising exchange.