The Privacy/Security Tradeoff for Multiple Secure Sketch Biometric Authentication Systems

When designing multiple biometric authentication systems, there is tension between minimizing privacy leakage and maximizing security. This work studies the tradeoff between the two measures for jointly designed "secure sketch" systems. Secure sketch is a biometric system architecture where, as with error-correcting codes, a system is characterized by a parity-check matrix over a finite field. Single systems have been widely researched, but little is known about the privacy and security of joint designs, when leakage of one system can compromise the security of the others. This work introduces worst-case measures of privacy leakage and security for sets of systems and studies the tradeoff between them: First by studying the algebraic structure of the problem, then through a continuous relaxation of the problem (in a restricted case) and performing optimizations. An analytic expression for the tradeoff in that restricted case is proposed which aligns with simulation results.