Provided is a technology including an apparatus and a machine-implemented method for operating a content sending apparatus attachable to a network, comprising acquiring a sequence comprising at least two content blocks; generating at least one authentication metadata block comprising at least one signed digest derived by a chaining digest technique from the sequence of content blocks; deriving a content transform encoding for each of the content blocks; and sending the at least one authentication metadata block and at least one content transform encoding to at least one of a set of recipient devices, the at least one device being operable to apply an inverse transformation to the content transform encoding and to authenticate at least one resultant content block according to the authentication metadata block.