  We analyze how secure a block is after the block becomes k-deep, i.e.,
security-latency, for Nakamoto consensus under an exponential network delay
model. We give parameter regimes for which transactions are safe when
sufficiently deep in the chain. We compare our results for Nakamoto consensus
under bounded network delay models and obtain analogous bounds for safety
violation threshold. Next, modeling the blockchain system as a batch service
queue with exponential network delay, we connect the security-latency analysis
to sustainable transaction rate of the queue system. As our model assumes
exponential network delay, batch service queue models give a meaningful
trade-off between transaction capacity, security and latency. As adversary can
attack the queue service to hamper the service process, we consider two
different attacks for adversary. In an extreme scenario, we modify the
selfish-mining attack for this purpose and consider its effect on the
sustainable transaction rate of the queue.
