Ericsson Ericsson Ericsson In order to support use cases when two or more end-points communicate via one (or more) cloud service (e.g. virtualized cloud-based conferencing) that are not trusted to access the media content, this document describes the use of so called end-to-end (inner) and hop- by-hop (outer) cryptographic transforms within the Secure Real-time Transport Protocol (SRTP). One of the main aspects of the transforms is to make the confidentiality and message authentication independent of the RTP header. Another central aspect is to enable identification of the cryptographic contexts (keys etc.). Besides the security of the end-points, also trust assumptions regarding the cloud services are addressed.