A plurality of encryption keys is generated, and each encryption key is associated with one geographical area of a plurality of geographical areas. Each encryption key is forwarded to one or more base stations in the geographical area associated with the encryption key. At least one of the plurality of geographical areas that is adjacent to a first geographical area is determined, yielding one or more adjacent geographical areas, and an encryption key for at least one of the one or more adjacent geographical areas is forwarded to at least one base station covering the first geographical area.