Abstract:

Along with the increasing reliance on computers and the Internet for myriad tasks from voting to auctions evolves a pressing need to develop cryptographic tools and protocols with stronger guarantees. Traditional cryptographic guarantees such as data privacy amidst wiretapping and security against a static collection of malicious network entities do not meet the security requirements for many of these tasks:

-- An adversary may be unable to learn your bid in an online auction if the bid is encrypted; however, it could potentially modify the ciphertext to obtain one corresponding to a bid that is a dollar higher than yours.

-- An adversary that adaptively determines which electronic voting machines to break into during the course of an election has a better chance at influencing the outcome of an election than one that makes its choices before the election commences.

I will present new constructions of encryption schemes addressing each of these attacks. The first scheme guarantees that given an encryption of a message, it is infeasible to generate an encryption of a related message. The second improves upon an important building block used in constructing protocols for general multi-party computation that are secure against an adversary that adaptively corrupts up to one third of the parties. Compared to most previous constructions, our schemes are simpler, more efficient, and can be realized under a larger class of cryptographic assumptions.