This paper is about trust establishment and trust evaluations techniques. A short background about trust, trusted computing and security in embedded systems is given. An analysis has been done of an incident network scenario with roaming users and a set of basic security needs has been identified. These needs have been used to derive security requirements for devices and systems, supporting the considered scenario. Using the requirements, a list of major security challenges for future research regarding trust establishment in dynamic networks have been collected and elaboration on some different approaches for future research has been done.This work was supported by the Knowledge foundation and RISE within the ARIES project.