Paper 2008/221

Efficient Conversion of Secret-shared Values Between Different Fields

Ivan Damgard and Rune Thorbek

Abstract

We show how to effectively convert a secret-shared bit $b$ over a prime field to another field. If initially given a random replicated secret share this conversion can be done by the cost of revealing one secret shared value. By using a pseudo-random function it is possible to convert arbitrary many bit values from one initial random replicated share. Furthermore, we generalize the conversion to handle general values of a bounded size.