With the advent of ubiquitous access to multimedia content via wireless networks, users are more likely to have their data traverse a heterogeneous internetwork. Given the open nature of the Internet and wireless links, more users will demand end-to-end confidentiality. However, because of inherent error-expansion properties of secret-key encryption, it is a challenge to provide good subjective quality and end-to-end confidentiality for multimedia data, particularly in network environments subject to both loss and corruption impairments. This paper analyzes the affect end-to-end confidentiality has on the quality of service (QoS) in Voice over IP (VoIP) networks. To satisfy a given QoS objective, we show that mitigating the error-expansion caused by confidentiality comes at a cost. We measure this cost by increased delay, reduced bandwidth, and reduced traffic capacity. Thus, for this class of applications, we motivate the need for error-robust encryption and introduce one such technique in this paper.