CCF implements write receipts, which are signed proofs associated with a transaction. They serve two main purposes:
Endorse claims made by the application logic, ie. a signed statement of fact, verifiable offline and by third parties, equivalent to “this transaction produced this outcome at this position in the ledger”.
Together with a copy of the ledger, or other receipts, they can be used to audit the service and hold the consortium to account.
Internally, receipts are also used to establish the validity of ledger snapshots.