Security on voice over internet protocol

Recently, Voice Over IP (VoIP) has been a very popular subject all over the world. VoIP presents more economical opportunities for both end users and the enterprises, because it can be integrated on the existing internet infrastructure, it does not need any further cost and decreases the setup and operational cost. Despite of all these constructive features, there are some difficulties that VoIP must overcome. The most important difficulty is the security issue. The VoIP traffic can be blocked, copied, changed or made slow by malicious people. In addition, the vulnerabilities of VoIP applications can damage the network systems of enterprises. In this study, security threats of VoIP, the possible results of these threats, the measures that can be taken against these threats and the most important security algorithms and protocols are investigated. Following this investigation, special applications that show the importance of these protocols are performed. At the end of these applications, it will be shown that the attacks against VoIP systems can be successful if the VoIP security protocols are disabled and then the attacks against VoIP systems are never successful if the VoIP security protocols are enabled. At the last section, a performance analyses that show negative effects of encryption algorithms on VoIP is performed. Keywords: VoIP, H.323, SIP, Security vulnerabilities of VoIP, VoIP security protocols, DES, AES, MD5, IPSec, TLS, SRTP.