BitCannery is the Ethereum-based dead-man-switch system. You save message to be delivered in case anything prevents you from using your Ethereum account. Then you check in every month to postpone delivery. As the message is free-form text and it's stored on Ethereum blockchain, where anyone has access to any data, system must employ a network of third-party 'key keepers', who hold encrypted parts of message so it isn't readable before the time.
