A method performed in a third computing device comprises: receiving a request from one of a first computing device and a second computing device; and in response to the request, facilitating establishment of a security association between the first computing device and the second computing device such that the first computing device and the second computing device can then facilitate establishment of a security association between first user equipment and second user equipment. The first computing device, the second computing device and the third computing device comprise at least a part of a key management hierarchy wherein the first computing device and the second computing device are on a lower level of the hierarchy and the third computing device is on a higher level of the hierarchy. The first and second computing devices are configured to perform a key management function for respective first and second user equipment.