An Efficient and DoS-resistant User Authentication Scheme for Two-tiered Wireless Sensor Networks for the purpose of implementation of two-tier authentication scheme [29]. WSNs for healthcare face issue of authentication in case of DoS attack. DoS attack can be resolved by implementing two-tier authentication scheme. First tier authenticates user by its unique identification and second tier authenticates by passing some parameters and accounting their response. Login requests have been validated and authenticated at server side based on saved data at the time of registration. Proposed security mechanism still faces replay, impersonation, DoS and other network attacks [30].