Methods for ad-hoc trust establishment using visual verification are described. In a first embodiment, a visual representation of a shared data is generated on two or more devices and the visual representations generated can be visually compared by a user. This method can be used to verify that the correct devices are involved in a negotiation, when pre-existing trust relationships do not exist between the devices. The visual representation may, for example, comprise a picture with a number of different elements, each representing a part of the shared data. In another embodiment, a method of secure key exchange is described in which, before sharing the keys, the parties exchange information which encapsulates the key. This information can be used subsequently to check that a party has not changed the key that they are using and prevents a man in the middle attack.