A media data security system for rendering a secure media data file, having associated authentication data, for output comprises a data preparation unit operable with respect to a version of the media data file, having user controls for generating a list of desired render operations to be applied to the media data file; and a secure data reproducer arranged to receive the list of desired render operations from the data preparation unit and to render the secure media data file for output on the basis of the list of render operations, the secure data reproducer comprising: a data authenticator for detecting the authenticity of the secure media data file using the authentication data; and a data reproducer operable, if the data authenticator detects that the input data is authentic, to perform the list of desired render operations with respect to the secure media data file.