  In this paper we address the issue of identity and access control within
shared permissioned blockchains. We propose the ChainAchor system that provides
anonymous but verifiable identities for entities on the blockchain. ChainAchor
also provides access control to entities seeking to submit transactions to the
blockchain to read/verify transactions on the the permissioned blockchain.
Consensus nodes enforce access control to the shared permissioned blockchain by
a simple look-up to a (read-only) list of anonymous members' public-keys.
ChainAnchor also provides unlinkability of transactions belonging to an entity
on the blockchain. This allows for an entity to optionally disclose their
identity when a transaction is called into question (e.g. regulatory or
compliance requirements), but without affecting the anonymity and unlinkability
of their remaining transactions.
