Privacy Enhancing Cryptographic Constructs for Cloud and Distributed Security
Sehrawat, Vipin Singh
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Despite commanding a significant market cap, the cloud is still not trusted with sensitive data due to security and privacy concerns. Secrecy of the data can be ensured by using a provably secure encryption scheme, but operating on the encrypted data in a secure and efficient manner remains a challenge. In this dissertation, we solve an open privacy related problem concerning key rotation, which is a highly desirable functionality for the cloud. Key rotation refers to periodically updating the cryptographic key material, that is used to encrypt the data. As the central piece of our solution, we define and construct two novel pseudorandom function families. Secret sharing is one of the most versatile and fundamental cryptographic tools for distributed security. It provides a means to distribute shares of a secret such that any authorized subset of shareholders, specified by a publicly known access structure, can recompute the secret. In this dissertation, we identify and address the need to bolster the privacy preserving aspects of secret sharing. We introduce three privacy preserving secret sharing classes along with novel mathematical structures (set-systems and vector families) and cryptographic protocols, that we use to realize them. The primary tools used in the constructions presented in this dissertation include combinatorics, linear algebra, hard problems in lattices, and number theory.