Secure Real-time Transport Protocol (SRTP) is an application protocol based on RFC3711. SRTP provides enhanced security features; thus, it secures RTP by encryption using an XOR operation with a keystream. The algorithm used is AES and the master key is called SRTP MKI. The following diagram illustrates the difference between a normal RTP packet and a secure RTP packet. The Auth field contains the message authentication code. These techniques provide anti-replay mechanisms to the voice traffic and ensure its integrity:
