Privacy-Preserving Biometric Authentication: Challenges and Directions

Box 2

Bloom Filters in Biometric Authentication. This method is the main alternative to the employment of leaking distances [29, 30].

Intuitively, a Bloom filter is an -bit string which represents a set (e.g., the acceptance area, and is the space of all

biometric templates). The encoding of into is done using independent hash functions in the

following way. For each element , and for each , the bits at positions of the Bloom filter are set to 1 (the other

bits are set to 0). To test if an element is in using the bloom filter, it is sufficient to check whether the bits of at positions

are 1, equal to for all . If this is the case, one can deduce that is in with high probability, otherwise it holds .

It is immediate to see that the employment of Bloom filters in the matching process directly mitigates any centre-search attack for

template recovery.