International Association
for Cryptologic Research

Helper data schemes are a security primitive used for privacy-preserving biometric databases and Physical Unclonable Functions.

One of the oldest known helper data schemes is the Code Offset Method (COM).

We propose an extension of the COM: the helper data is accompanied by many instances of fake helper data that is drawn from the same distribution as the real one.

While the adversary has no way to distinguish between them, the legitimate party has more information and *can* see the difference.

We use an LDPC code in order to improve the efficiency of the legitimate party\'s selection procedure.

Our construction provides a new kind of trade-off: more effective use of the source entropy, at the price of increased helper data storage.

We give a security analysis in terms of Shannon entropy and order-2 Renyi entropy.