A method for protecting content on a medium (120), the method including providing a medium (120) including a token (130), the token (130) implementing at least a portion of a keyed function, providing a plurality of token inputs, each token input being suitable for input to the token (130), providing a first encryption method and a first encryption key, for each one of the plurality of token inputs inputting the token input to the token and receiving a token output from the token, and converting the token output to a function output, the function output representing a result of performing the keyed function on a function input corresponding to the token input, and storing an ordered pair including the function input and the function output, thereby producing a plurality of ordered pairs (160), encrypting the plurality of ordered pairs (160) using the first encryption method and the first encryption key, thereby producing an encrypted plurality of ordered pairs (170), and storing the encrypted plurality of ordered pairs (170) on the medium. Related apparatus and methods are also described.