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For many wireless sensor networks, high accuracy and low complexity localization techniques are crucial to their successful deployment. The radio interferometric positioning system (RIPS) has been introduced for accurate localization with low complexity. In this paper, a dual-tone radio interferometric positioning system (DRIPS) is proposed to localize multiple targets simultaneously. In DRIPS, multiple asynchronous targets emit dual-tone signals, and synchronous anchor receivers (nodes with known positions) extract phase information of low-frequency differential tones created by squaring the received dual-tone signals. Multiple time-of-arrivals (TOAs) coupled with unknown offsets due to the asynchronous targets are estimated based on the phase information. Accordingly, a localization algorithm taking the integer ambiguity issue into account is developed. Moreover, considering the case without accurate knowledge of the frequencies of the differential tones, an ESPRIT-type algorithm is proposed to estimate the frequencies. The proposed DRIPS is robust to flat-fading channels, immune to uncertainties of local oscillators, and able to distinguish different targets. In order to show more insights of the performance limit of the DRIPS, Cramér-Rao bounds (CRBs) are derived. Simulation results illustrate the merits of the proposed DRIPS.