Protecting Biometric Features by Periodic Function-Based Transformation and Fuzzy Vault - Transactions on Large-Scale Data-and Knowledge-Centered Systems - page 65

Fig. 3. Mapping two distant points into new two closed points

Fig. 4. New sine transformation

3.5 Fuzzy Vault Encoding

The key K is 144-bit which is randomly generated by a random number generator.
This key is used for polynomial construction in fuzzy vault scheme. At first, a 8-order
polynomial, , needs to be generated. The values
of these coefficients are created by truncating the 144-bit K to 9 non-overlapping
16-bit segments. And then, each of them is mapped to the coefficients in
succession. For example, the first 16 bits is mapped to , and so on. The order of the
mapping should be preserved for encoding and decoding of the vault.
To create the genuine points, the polynomial is evaluated on each of the
transformed feature points . As a result, the genuine set G consists of a set of pairs
, , where M is the dimension of the feature vector (also is the dimension
of the transformed features). The next step we need to do is to generate the chaff