Improved Proxy Re-Encryption Schemes with Applications to Secure Distributed Storage
In 1998, Blaze, Bleumer, and Strauss (BBS) proposed an application called atomic proxy re-encryption, in which a semi-trusted proxy converts a ciphertext for Alice into a ciphertext for Bob without seeing the underlying plaintext. We predict that fast and secure re-encryption will become increasingly popular as a method for managing encrypted file systems. Although efficiently computable, the wide-spread adoption of BBS re-encryption has been hindered by considerable security risks. Following recent work of Ivan and Dodis, we present new re-encryption schemes that realize a stronger notion of security and we demonstrate the usefulness of proxy re-encryption as a method of adding access control to the SFS read-only file system. Performance measurements of our experimental file system demonstrate that proxy re-encryption can work effectively in practice.
Key Regression: Enabling Efficient Key Distribution for Secure Distributed Storage
The Plutus file system introduced the notion of key rotation as a means to derive a sequence of temporally-related keys from the most recent key. In this paper we show that, despite natural intuition to the contrary, key rotation schemes cannot generically be used to key other cryptographic objects; in fact, keying an encryption scheme with the output of a key rotation scheme can yield a composite system that is insecure. To address these shortcomings, we introduce a new cryptographic object called a key regression scheme, and we propose three constructions that are provably secure under standard cryptographic assumptions. We implement key regression in a secure file system and empirically show that key regression can significantly reduce the bandwidth requirements of a content publisher under realistic workloads using lazy revocation. Our experiments also serve as the first empirical evaluation of either a key rotation or key regression scheme.