How to tell which of the encrypted numbers is greater

Vlad Kolesnikov
Department of Computer Science
University of Toronto


We consider the problem of comparing two encrypted numbers and its extension -- transferring one of the two secrets, depending on the result of comparison. We show how to efficiently apply our solutions to practical settings, such as auctions with the semi-honest auctioneer, proxy selling, etc. We propose a new primitive, Conditional Encrypted Mapping, which captures common security properties of one round protocols in a variety of settings, which may be of independent interest.

This work will appear in the proceedings of the Financial Cryptography and Data Security Conference 2006, and is available from

Colloquia Series page.