VoIP has developed into a specialized voice communication technology currently, whose application is wider and wider. But the research shows that the security is the main content considered by the enterprise when VoIP is decided besides the service quality issue. In the real application, the reason that the enterprise doesn't want to deploy VoIP is that the security situation can't reach the application standard. This article studies the secure hash algorithm, discusses its implementation process and carries out the implementation of VC. Real-time voice encryption is completed by using the combination between elliptic curve cryptography and SHA, and the encryption between voice and data.