1. A computer-implemented method comprising: receiving, by a computing device, a criteria-encoded message that encodes criteria for selecting a recipient of a digital coupon; generating, by the computing device, a user-behavior vector that includes one or more vector entries, wherein a respective vector entry includes a numeric value that characterizes a user behavior for the end-user; producing, by the computing device, a behavior-encoded message that encodes the end-user's behavior pattern, wherein producing the behavior-encoded message involves using a hash function to encode the user-behavior vector; determining, by the computing device, that the end-user is eligible to receive the digital coupon in response to detecting a match between the criteria-encoded message and the behavior-encoded message; and providing, by the computing device, the digital coupon to the end-user in response to determining that the user is eligible.