This work introduces two new cryptographic protocols of different complexity and strength in limiting network degradation caused by sinkhole attacks on tree-based routing topologies in Wireless Sensor Networks (WSNs). The main goal of both protocols is to provide continuous operation by improving resilience against, rather than detection of, these attacks. The main benefit of providing resilience is that it allows operating (or graceful degradation) in the presence of attacks. Furthermore, while resilience mechanisms do not dismiss detection mechanisms, detection mechanisms often introduce more complexity and so, more weaknesses to the system, which might not justify their benefits. We provide a simulation study of the two protocols for three different routing protocols, that encompass typical routing strategies used in WSN. The results of our simulation study show that our cryptographic protocols are effective in improving resilience against sinkhole attacks, even in the presence of some collusion.