## Cryptology ePrint Archive: Report 2014/024

**An Efficient Pseudo-Random Generator with Applications to Public-Key Encryption and Constant-Round Multiparty Computation**

*Ivan Damgård and Jesper Buus Nielsen*

**Abstract: **We present a pseudo-random bit generator expanding a uniformly random bit-string r of length k/2, where k is the security parameter, into a pseudo-random bit-string of length 2k − log^2(k) using one modular exponentiation. In contrast to all previous high expansion-rate pseudo-random bit generators, no hashing is necessary. The security of the generator is proved relative to Paillier’s composite degree residuosity assumption. As a first application of our pseudo-random bit generator we exploit its efficiency to optimise Paillier’s crypto-system by a factor of (at least) 2 in both running time and usage of random bits. We then exploit the algebraic properties of the generator to construct an efficient protocol for secure constant-round multiparty function evaluation in the cryptographic setting. This
construction gives an improvement in communication complexity over previous protocols in the order of nk^2, where n is the number of participants and k is the security parameter, resulting in a communication complexity of O(nk^2|C|) bits, where C is a Boolean circuit computing the function in question.

**Category / Keywords: **cryptographic protocols /

**Date: **received 8 Jan 2014

**Contact author: **jbn at cs au dk

**Available format(s): **PDF | BibTeX Citation

**Note: **This paper was made public on the homepage of one of the authors almost a decade ago. It was never published elsewhere. However, it has by now been cited a number of times, so we make it available on eprint for archival purposes / future availability.

**Version: **20140108:175216 (All versions of this report)

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