user A wants to keep some data safe (encrypted) in contract; user B can access A's data only if A does not prevent access
user B can claim access by entering a key previously given by A on the contact platform. The contract asks A if the information can be release to B each time B claims access. A has a certain period (i.e. N days) to stop information release. Failing to stop the release or denying access after the given period, data are opened (decrypted) and accessible to B.
Does such contract or service already exists in blockchain ?