A computer-implemented method includes generating data indicative of one or more times in which to sample content of a first resource and content of a second resource; receiving, from a client device, content of the first resource sampled at the one or more times; comparing the sampled content from the first resource to content sampled from the second resource at the one or more times; determining, based on comparing, that the first resource includes a same resource as the second resource; verifying, based on determining, ownership of the second resource; generating, based on a verifying, a user key specifying ownership of the second resource; and transmitting the user key to the client device.