  The mempool plays a crucial role in blockchain systems as a buffer zone for
pending transactions before they are executed and included in a block. However,
existing works primarily focus on mitigating defenses against already
identified real-world attacks. This paper introduces secure blockchain-mempool
designs capable of defending against any form of asymmetric eviction DoS
attacks. We establish formal security definitions for mempools under the
eviction-based attack vector. Our proposed secure transaction admission
algorithm, named \textsc{saferAd-CP}, ensures eviction-security by providing a
provable lower bound on the cost of executing eviction DoS attacks. Through
evaluation with real transaction trace replays, \textsc{saferAd-CP}
demonstrates negligible latency and significantly high lower bounds against any
eviction attack, highlighting its effectiveness and robustness in securing
blockchain mempools.
