A computer based method and apparatus to tie content protection information to recipient devices via a family of deterministic permutations of quadratic multivariate polynomial maps used for computing an HMAC (Hash Message Authentication Code) or a signed digest. This allows digital rights management (DRM) systems to customize the protection information (such as an HMAC or signed digest) for audio and video content, whereby such protection information for a piece of content differs for different recipient devices or for types of recipient devices.