Automatic speaker verification (ASV) systems are vulnerable to spoofing attacks using speech generated by voice conversion and speech synthesis techniques. Commonly, a countermeasure (CM) system is integrated with an ASV system for improved protection against spoofing attacks. But integration of the two systems is challenging and often leads to increased false rejection rates. Furthermore, the performance of CM severely degrades if in-domain development data are unavailable. In this study,

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... fore, we propose a solution that uses two separate background models -one from human speech and another from spoofed data. During test, the ASV score for an input utterance is computed as the difference of the log-likelihood against the target model and the combination of the log-likelihoods against two background models. Evaluation experiments are conducted using the joint ASV and CM protocol of ASVspoof 2015 corpus consisting of text-independent ASV tasks with short utterances. Our proposed system reduces error rates in the presence of spoofing attacks by using out-of-domain spoofed data for system development, while maintaining the performance for zero-effort imposter attacks compared to the baseline system.