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 http://www.cs.toronto.edu/~vlad/
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