This specification describes technologies relating to imparting cryptographic information in network communications. In general, aspects of the subject matter described in this specification can be embodied in methods that include identifying a location in a pre-defined portion of a network communication to be sent in a client-server environment, wherein the pre-defined portion is reserved for random data, inserting cryptographic information into the pre-defined portion of the network communication at the location, and sending the network communication in the client-server environment to facilitate modifying interactions in the client-server environment based at least in part on a result of processing of the cryptographic information; and on a receiving side, receiving cryptographic information inserted into the pre-defined portion of the network communication in the client-server environment, identifying the location, processing the cryptographic information, and modifying interactions in the client-server environment based at least in part on a result of the processing.