  Propelled by the growth of large-scale blockchain deployments, much recent
progress has been made in designing sharding protocols that achieve throughput
scaling linearly in the number of nodes. However, existing protocols are not
robust to an adversary adaptively corrupting a fixed fraction of nodes. In this
paper, we propose Free2Shard -- a new architecture that achieves near-linear
scaling while being secure against a fully adaptive adversary.
  The focal point of this architecture is a dynamic self-allocation algorithm
that lets users allocate themselves to shards in response to adversarial
action, without requiring a central or cryptographic proof. This architecture
has several attractive features unusual for sharding protocols, including: (a)
the ability to handle the regime of large number of shards (relative to the
number of nodes); (b) heterogeneous shard demands; (c) requiring only a small
minority to follow the self-allocation; (d) asynchronous shard rotation; (e)
operation in a purely identity-free proof-of-work setting. The key technical
contribution is a deep mathematical connection to the classical work of
Blackwell in dynamic game theory.
