Specific techniques to apply encryption has been developed especially for "classic", or "normal", SIP (as opposed to SIP over WebRTC, see later).
SIP encryption is based on two concepts - encrypting signaling and encrypting media (audio/video) communication. Like any standard encryption mechanism, SIP encryption utilizes standard cryptography libraries and involves key exchanges and password negotiation to securely transmit and receive information. The main encryption algorithms used in SIP (which are detailed later) are very similar to SSL over the web and key exchange is used when connecting to remote servers via SSH. In either exchange, the main goal is to end up with an encryption algorithm and a common encryption secret between the two parties that only they know, which can be used to encrypt and decrypt...
