  Proof of Work (PoW) blockchains are susceptible to adversarial majority
mining attacks in the early stages due to incipient participation and
corresponding low net hash power. Bootstrapping ensures safety and liveness
during the transient stage by protecting against a majority mining attack,
allowing a PoW chain to grow the participation base and corresponding mining
hash power. Liveness is especially important since a loss of liveness will lead
to loss of honest mining rewards, decreasing honest participation, hence
creating an undesired spiral; indeed existing bootstrapping mechanisms offer
especially weak liveness guarantees.
  In this paper, we propose Advocate, a new bootstrapping methodology, which
achieves two main results: (a) optimal liveness and low latency under a
super-majority adversary for the Nakamoto longest chain protocol and (b)
immediate black-box generalization to a variety of parallel-chain based scaling
architectures, including OHIE and Prism. We demonstrate via a full-stack
implementation the robustness of Advocate under a 90% adversarial majority.
