| Helger Lipmaa's publications |
Sven Laur and Helger Lipmaa. A New Protocol for Conditional Disclosure of Secrets And Its Applications. In Jonathan Katz and Moti Yung, editors, The Fifth International Conference on Applied Cryptography and Network Security (ACNS'07), volume 4521 of Lecture Notes in Computer Science, pages 207--225, Zhuhai, China, June 5--8, 2007. Springer-Verlag.
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Abstract:
Many protocols that are based on homomorphic encryption are private only if a client submits inputs from a limited range $S$. Conditional disclosure of secrets (CDS) helps to overcome this restriction. In a CDS protocol for a set $S$, the client obtains server's secret if and only if the client's inputs belong to $S$ and thus the server can guard itself against malformed queries. We extend the existing CDS protocols to work over additively homomorphic cryptosystems for every set from $\mathbf{NP/poly}$. The new construction is modular and easy to apply. As an example, we derive a new oblivious transfer protocol with log-squared communication and a millionaire's protocol with logarithmic communication. We also implement private, universally verifiable and robust multi-candidate electronic voting so that all voters only transmit an encryption of their vote. The only hardness assumption in all these protocols is that the underlying public-key cryptosystem is IND-CPA secure and the plaintext order does not have small factors..
Keywords: Conditional disclosure of secrets, crypto-computing, homomorphic encryption, oblivious transfer, two-party computation.
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