Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for storing and retrieving encrypted data. In one aspect, a method includes receiving, at a server computer separate from a user device, a first encrypted resource encrypted by use of a public encryption key, wherein the public encryption key is paired with a private encryption key according to an asymmetric encryption key scheme; retrieving, by the server computer, a second encrypted resource encrypted by use of the public key; augmenting, by the server computer, the first encrypted resource with the second encrypted resource to form an encrypted data tuple; encrypting, by the server computer, the encrypted data tuple; and storing, by the server computer, the encrypted data tuple as the second encrypted resource.