The NuCypher network uses the Umbral threshold proxy re-encryption scheme to provide cryptographic access controls for distributed apps and protocols.
Alice, the data owner, encrypts data with her public key and uploads it to IPFS, Swarm, S3, or any other storage layer. To delegate access to valid recipients, she creates and uploads re-encryption keys to the NuCypher network.
Ursula, a miner, receives the re-encryption keys and stands ready to re-key data in exchange for payment in fees and block rewards. Ursula and the storage layer never have access to Alice's plaintext data.
Bob, a data recipient, sends an access request to the NuCypher network. If a valid re-encryption key exists, the data is re-keyed to his public key and he can decrypt with his private key.