Abstract: Techniques are disclosed relating to performing session verification for a session between a client computer system and a server computer system. In some embodiments, a server computer system may perform session verification by initially performing a first session verification operation followed by iterations of a second session verification operation. In some embodiments, a given iteration of the iterations of the second verification operation may include receiving, from the client computer system, client authentication information that includes first and second authentication values. Further, in some embodiments, a given iteration may include determining a server authentication value that is based on the first authentication value and authentication information previously received from the client computer system during session verification.