Bitcannery is a system designed to provide an encryption with extendable self-decryption time. In a nutshell, such encryption ensures that a message is automatically decrypted after a certain point in the future. This point in time can be continuously extended by the sender of the message.
Real life applications may include data escrow, leaking, last-resort backups, inheritance, insurance and even a simple data storage.
At the moment it is implemented on the Ethereum blockchain and deployed to the Rinkeby testnet, but it doesn't have to be limited to Ethereum. Bitcannery system can be generalized for virtually any distributed ledger supporting smart contracts.
You have an information you want to keep. We call it a "secret" and you are a "secret owner" in this scenario.
Using Bitcannery, you encode a secret locally with the first key.
Bitcannery generates a second key, encodes the secret one more time and publishes the double encrypted secret on the blockchain.
Using Bitcannery, you perform a predefined periodic action (run some script or visit some website). We call it a "check-in".
Keepers are unaware of which secret they're keeping, so even if majority of the keepers are malicious it's very hard for them to reconstruct a complete key. For a succesful Sybil attack, 66% of all keepers would have to cooperate. Even if it's done somehow (by identifying the existing keepers or by flooding the system with the new ones), the attacker would only get the data encrypted with the first key, kept privately by the secret owner.
To motivate the keepers, simple monetary model is used. Every keeper earns a fee for performing his/her part. Fee is set by the secret owner, so it's up to each keeper to accept specific keeping contract or not.
There is a rating system planned which would make sure stable and honest keepers are paid higher (not implemented yet).