Updating key information

A method of providing key information from a sender to one or more receivers, the method comprising: obtaining initial key information comprising a plurality of units that assume respective values; forming encoded key information from the initial key information, wherein the encoded key information comprises a plurality of encoded units that correspond to respective units of the initial key information, wherein said forming comprises, for each unit of the initial key information, selecting an encoding from a plurality of invertible encodings associated with said unit and encoding said value assumed by said unit with said selected encoding to form the corresponding encoded unit; and providing the encoded key information to said one or more receivers.