The present invention relates to method for operating a trust center for distributing key material to at least one radio station, comprising the steps of at the trust center, dividing an identifier of the radio station, said identifier being a code word consisting a first number of bits, into a plurality of subidentifiers, and generating for each subidentifier, an keying material function selected out of a set of keying material functions on the basis of the considered subidentifier at the trust center, transmitting to the radio station the identifier and the key material comprising the generated encryption functions.