Calypso allows a writer to encrypt a document, and to store the list of allowed readers on a blockchain. Over time, the writer can update this list to include more readers, or to remove readers that they don't trust anymore. The blockchain will verify all read requests and log them immutably. Only authorized read-requests will receive the decryption key.

This has a big advantage over current document encryption schemes, which suffer from:

• a trusted central authority that might be hacked or forced to behave maliciously
• the need to know all readers in advance, and not knowing which of them will access the documents

Applications

• Clearance-enforcing Document Sharing - as implemented in the Odyssey pilot, which allows Auditable Sharing and Management of Sensitive Data Across Jurisdictions: the documents are stored encrypted, and only available to a restricted set of readers. The access control is updatable, and all accesses are logged in a blockchain.
• Patient-centric Medical Data sharing - in a medical setting, the data gathered about a patient need to be secured. The patient needs to be in the position of adding and revoking access to their data. This can be done easily with Calypso.
• Decentralized Games - a number of online games using the blockchain start to emerge. Some of them need to consider secret moves of the players before calculating the winner. For example a lottery, poker, but also bidding. Calypso can store all these moves encrypted and enforce the decryption only to happen once a barrier point is passed - either a certain time, or a number of moves stored.