Systems and methods for collecting audience measurement data using content protection signaling messages while playing back content are disclosed. One embodiment includes receiving content, where content is encrypted using at least one encryption key, receiving a content protection signaling message, where the content protection signaling message is associated with the content and includes a reference timestamp and decryption information associated with the content, processing the content protection signaling message to extract the reference timestamp and the decryption information and generating a message processing timestamp based on the time the content protection signaling message is processed, collecting audience measurement data and saving the audience measurement data into memory, where the audience measurement data includes the reference timestamp and message processing timestamp, recovering at least one decryption key using the decryption information, and decrypting the content using the at least one decryption key.