Secure Real-time Transport Protocol
Encryption mechanisms for VoIP have been specified since the introduction of VoIP services. One such is the Secure Real-time Transport Protocol (SRTP). SRTP, as defined in RFC 3711, provides confidentiality, integrity, and authentication for the communications path between two end devices. The encryption and key management are provided by the Advanced Encryption Standard (AES-CM); authentication and message integrity are provided by HMAC-SHA1 algorithms. Few devices today in the enterprise realm offer voice encryption capabilities using SRTP.