A method for protecting content on a medium including a token which implements at least a portion of a keyed function, providing a first encryption method and a first encryption key, inputting each one of a plurality of token inputs to the token and converting an output of the token to a function output, and storing a plurality of ordered pairs each including a function input and the corresponding function output, encrypting the plurality of ordered pairs using the first encryption method and the first encryption key, and storing the encrypted plurality of ordered pairs on the medium. Related apparatus and methods are also described.