The problem of designing a decentralized Cooperative Adaptive Cruise Control (CACC) resilient to Denial-of-Service (DoS) attacks while satisfying performance requirements is studied. A decentralized proportional-derivative hybrid controller is employed for string stability of a platoon of vehicles. A timer triggering the arrival of new measurements from preceding vehicles augments the closed-loop system. A computationally affordable algorithm based on matrix inequalities is devised to design a CACC controller able to meet performance specifications and to guarantee string stability up to an estimated number of consecutive packet dropouts. Finally, the effectiveness of the proposed approach is shown in a numerical example.