  This paper presents secure mempool designs under asymmetric DoS attacks. We
formulate safety definitions under two abstract DoSes, namely eviction- and
locking-based attacks.
  We propose a safe transaction admission framework for securing mempools,
named saferAd, that achieves both eviction- and locking-safety. The proven
security stems from an upper bound of the attack damage under locking DoSes and
a lower bound of the attack cost under eviction DoSes. The evaluation by
replaying real transaction traces shows saferAd incurs negligible latency or
insignificant change of validator revenue.
