A method provides a collection of data structures and subroutines in a software toolkit, for developing an application for playing digital content data. The method comprises steps of receiving previously encrypted content data encrypted with an encrypted key from an external source; storing the previously encrypted content data in a library; selecting one or more encrypted content data from the library to play; and decrypting each content data selected to be played with its unique encryption key, wherein the decrypting is performed in a tamper-resistant subroutine for deterring unauthorized access to the instructions for decrypting the content data and for deterring unauthorized access to the encryption key.