Voice over Internet Protocol is a technology that enables people to use the Internet, rather than the traditional public switched telephone network, as the transmission medium for voice communications. VoIP is becoming increasingly popular due to its significant advantages in cost and flexible features compared with the plain old telephone system. The proliferation of VoIP calls has significant implications on the security and privacy aspects of voice calls. For example, the use of VoIP has made it much easier to achieve confidentiality and anonymity in voice communications. On the other hand, VoIP has imposed significant new challenges in providing the same call-identifying and wiretapping capabilities as those that exist in traditional circuit-switched networks. In this article we examine the privacy and security aspects of peer-to-peer (P2P) VoIP calls and show how the use of VoIP has substantially shifted the previous balance between privacy and security that exists in traditional PSTN calls. In particular, we show that the use of strong encryption and available low-latency anonymizing network at the same time does not necessarily provide the level of anonymity to VoIP that people would intuitively expect.
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