The Ledger is a blockchain platform based on Hyperledger Sawtooth technologies. Its purpose is essentially to allow the formalization of links between users, datasets and sharing agreements. Its hosting mode aligns well with the decentralized approach of the Orchestrator and allows operation by several independent partners.
Despite the decentralized deployment approach, access to the blockchain is through a middleware application and not directly in the way cryptocurrencies are. In this sense, access key security should be ensured by limiting the entry points to a single external api. This bridge constrains potential access paths and limits attack surfaces on the blockchain. It also allows better control of version migrations of the different components and avoids regression bugs by controlling potential usage scenarios.