Decentralizing Attribute-Based Encryption.
Allison Bishop Lewko, Brent R. Waters · 2010
Abstract. We propose a Multi-Authority Attribute-Based Encryption (ABE) system. In our system, any party can become an authority and there is no requirement for any global coordination other than the cre-ation of an initial set of common reference parameters. A party can sim-ply act as an ABE authority by creating a public key and issuing private keys to different users that reflect their attributes. A user can encrypt data in terms of any boolean formula over attributes issued from any cho-sen set of authorities. Finally, our system does not require any central authority. In constructing our system, our largest technical hurdle is to make it collusion resistant. Prior Attribute-Based Encryption systems achieved collusion resistance when the ABE system authority “tied ” together dif-ferent components (representing different attributes) of a user’s private key by randomizing the key. However, in our system each component will come from a potentially different authority, where we assume no coor-dination between such authorities. We create new techniques to tie key components together and prevent collusion attacks between users with different global identifiers. We prove our system secure using the recent dual system encryp-tion methodology where the security proof works by first converting the challenge ciphertext and private keys to a semi-functional form and then arguing security. We follow a recent variant of the dual system proof technique due to Lewko and Waters and build our system using bilin-ear groups of composite order. We prove security under similar static assumptions to the LW paper in the random oracle model. 1