  Hashing technology gains much attention in protecting the biometric template
lately. For instance, Index-of-Max (IoM), a recent reported hashing technique,
is a ranking-based locality sensitive hashing technique, which illustrates the
feasibility to protect the ordered and fixed-length biometric template.
However, biometric templates are not always in the form of ordered and
fixed-length, rather it may be an unordered and variable size point set e.g.
fingerprint minutiae, which restricts the usage of the traditional hashing
technology. In this paper, we proposed a generalized version of IoM hashing
namely gIoM, and therefore the unordered and variable size biometric template
can be used. We demonstrate a realization using a well-known variable size
feature vector, fingerprint Minutia Cylinder-Code (MCC). The gIoM transforms
MCC into index domain to form indexing-based feature representation.
Consequently, the inversion of MCC from the transformed representation is
computational infeasible, thus to achieve non-invertibility while the
performance is preserved. Public fingerprint databases FVC2002 and FVC2004 are
employed for experiment as benchmark to demonstrate a fair comparison with
other methods. Moreover, the security and privacy analysis suggest that gIoM
meets the criteria of template protection: non-invertibility, revocability, and
non-linkability.
