  In the proof-of-stake (PoS) paradigm for maintaining decentralized,
permissionless cryptocurrencies, Sybil attacks are prevented by basing the
distribution of roles in the protocol execution on the stake distribution
recorded in the ledger itself. However, for various reasons this distribution
cannot be completely up-to-date, introducing a gap between the present stake
distribution, which determines the parties' current incentives, and the one
used by the protocol. In this paper, we investigate this issue, and empirically
quantify its effects. We survey existing provably secure PoS proposals to
observe that the above time gap between the two stake distributions, which we
call stake distribution lag, amounts to several days for each of these
protocols. Based on this, we investigate the ledgers of four major
cryptocurrencies (Bitcoin, Bitcoin Cash, Litecoin and Zcash) and compute the
average stake shift (the statistical distance of the two distributions) for
each value of stake distribution lag between 1 and 14 days, as well as related
statistics. We also empirically quantify the sublinear growth of stake shift
with the length of the considered lag interval. Finally, we turn our attention
to unusual stake-shift spikes in these currencies: we observe that hard forks
trigger major stake shifts and that single real-world actors, mostly exchanges,
account for major stake shifts in established cryptocurrency ecosystems.
