chaff

In the proposed approach, the chaffs are generated by using the user's minutiae direction information.

For each user's minutia, the chaffs are inserted along the line by adding/subtracting [DELTA]x and [DELTA]y to/from the x-y coordinates of the minutia.

The average number of minutiae was 30, and we inserted about 200, 300, and 400 chaffs, respectively.

Additionally, for the purpose of evaluating the security level against the correlation attack, we compared the performance of the structured chaff insertion approach (i.e., the chaffs are generated by using the user's minutiae direction information) with that of random chaff insertion approach (i.e., we implemented it based on [8] to evaluate the security level).

Additionally, to avoid the correlation attack against the fuzzy vault, we applied an approach to insert chaffs in a structured way such that distinguishing the fingerprint minutiae and the chaff points obtained from two applications is computationally hard.

Additionally, to hide these "real" minutiae, numerous "chaff minutiae are encoded, in which the value of f([a.sub.i]) is random.