Template Protection: On the need to adapt the current Unlinkability Evaluation Protocol

Abstract

Using ISO/IEC Standards an evaluation protocol exists which properties need to be fulfilled by each template protection scheme. However, in these standards it is not defined how a sensible and sensitive key selection should be done such that the demanded properties are reached. For the analysis regarding the ISO/IEC Standards properties only arbitrary, randomly selected keys are usually used, but it is not considered that in this case the key selection might result in insufficiently protected biometric images (templates). By the performed experiments using not only randomly selected keys, but also considering the best of insufficient (improper) keys, it was revealed that the unlinkability evaluation protocol is influenced by the key selection. Hence, it is recommended to use both mentioned key types to analyse template protection methods. This means that the protocol has to be fine-tuned, in so far that for the best of the worst key choice (which then has to be used in the protocol) unlinkability still needs to be given.