An authentication apparatus for authentication of a physical object having privacy sensitive biometric data comprising an enrolment means (ENRL), and an authentication means (AUTH), wherein said enrolment means are arranged in - measuring biometric reference characteristics of said physical object having privacy sensitive biometric data; - constructing and storing biometric template data from said measured blometric reference characteristics; - producing and storing a helper data from said biometric template data - producing and storing a control value; the authentication means being arranged in: measuring a biometric from the physical object having privacy sensitive biometric data to be authenticated; and further comprising: - a first generation means arranged to produce a first property set from the helper data and the biometric measured from the physical object, - a second generation means arranged to apply a noise compensating mapping on said first property data set to compensate for measured noise in said biometric thereby obtaining a second property set, - a comparing means arranged to establish a sufficient match between the physical object having privacy sensitive biometric data and the reference object having privacy sensitive blometric data, by verifying whether the second property set is within a classification boundary of the reference object using the first control value and wherein the noise robust mapping determines the classification boundary, the authentication apparatus characterized in that It further comprises: - a third generation means which obtain an error measure by quantifying the noise removed by the noise compensating mapping using the first property set and the second property set, and - an authentication decision means arranged to use said error measure sent to said authentication decision means to establish an authentication decision. - measuring biometric reference characteristics of said physical object having privacy sensitive biometric data; - constructing and storing biometric template data from said measured blometric reference characteristics; - producing and storing a helper data from said biometric template data - producing and storing a control value; measuring a biometric from the physical object having privacy sensitive biometric data to be authenticated; - a first generation means arranged to produce a first property set from the helper data and the biometric measured from the physical object, - a second generation means arranged to apply a noise compensating mapping on said first property data set to compensate for measured noise in said biometric thereby obtaining a second property set, - a comparing means arranged to establish a sufficient match between the physical object having privacy sensitive biometric data and the reference object having privacy sensitive blometric data, by verifying whether the second property set is within a classification boundary of the reference object using the first control value and wherein the noise robust mapping determines the classification boundary, the authentication apparatus characterized in that It further comprises: - a third generation means which obtain an error measure by quantifying the noise removed by the noise compensating mapping using the first property set and the second property set, and - an authentication decision means arranged to use said error measure sent to said authentication decision means to establish an authentication decision.