channel such as a separate frequency band or physical channel or rather a virtual channel such as being provided by particular bit positions that would be necessary anyway usually the first situation will apply now receiver block 26 will execute the decrypting procedure to ultimately reproduce unsecured content 28 the nature of the transmitting and receiving facilities and also the overall structure or usage of the transmitted data are generally inconsequential to the present invention fig2 a u2013 2 c illustrate a basic sketch of a key update flow according to the present invention the encryption requirement will not allow to insert additional bits next to what is necessary to transmit the secured content proper nor allow the compression of the content in such situation all control information must be transmitted out of band therefore there is not necessarily a strict temporal connection between the two information structures 24 30 in fig1 but a delay possibly a variable one may therebetween be present an example of such secured link being planned for the future is a so called spdif standard that will protect all of a digital audio band between a compliant source device and a compliant destination device of course other transfer than audio such as video or multimedia would potentially benefit from the present invention in fig2 a the transition to the next encryption key at the source device 22 has not yet been effected but is planned for execution as indicated by arrow 21 in fig2 b the transition has at the source device 22 been effected indeed so that its actual notional location may be suggested by arrow 25 note that input or output.