Session Description Protocol Security Descriptions (SDES) is a mechanism used to secure the end-to-end communication of Real-time Transport Protocol (RTP) streams between endpoints in Voice over IP (VoIP) and video conferencing applications. It provides a way to negotiate encryption keys and cryptographic parameters between the endpoints in real-time to ensure that the communication is secured from eavesdropping and tampering. SDES is a specialized skill that requires knowledge of cryptographic protocols, key management, VoIP technologies, and network security.