Abstract (EN)

We propose a scheme using client-side encryption with symmetric keys for the privacy of data outsourced to the cloud for selected readers. The scheme is safe under the most popular "honest, but curious" model. Readers get the keys from access grants or have them cached. LH* files store cloud data and metadata. Diffie-Hellman scheme authenticates clients. Every client can read any data, but only a grantee decrypts the content. Access to data is usually the fastest possible that is two messages and the decryption, regardless of the cloud scale up. Data or grant creation or update costs are also constant with a few messages and fast processing. All these features serve our main goal: the search speed and scalability yet unmatched to our best knowledge. The scheme is finally intentionally very simple.