  Permissioned ledger technologies have gained significant traction over the
last few years. For practical reasons, their applications have focused on
transforming narrowly scoped use-cases in isolation. This has led to a
proliferation of niche, isolated networks that are quickly becoming data and
value silos. To increase value across the broader ecosystem, these networks
must seamlessly integrate with existing systems and interoperate with one
another. A fundamental requirement for enabling crosschain communication is the
ability to prove the validity of the internal state of a ledger to an external
party. However, due to the closed nature of permissioned ledgers, their
internal state is opaque to an external observer. This makes consuming and
verifying states from these networks a non-trivial problem.
  This paper addresses this fundamental requirement for state sharing across
permissioned ledgers. In particular, we address two key problems for external
clients: (i) assurances on the validity of state in a permissioned ledger and
(ii) the ability to reason about the currency of state. We assume an
adversarial model where the members of the committee managing the permissioned
ledger can be malicious in the absence of detectability and accountability. We
present a formalization of the problem for state sharing and examine its
security properties under different adversarial conditions. We propose the
design of a protocol that uses a secure public ledger for providing guarantees
on safety and the ability to reason about time, with at least one honest member
in the committee. We then provide a formal security analysis of our design and
a proof of concept implementation based on Hyperledger Fabric demonstrating the
effectiveness of the proposed protocol.
