The invention is directed to a source device and a method for encrypting digital contents at the source device. According to an embodiment, the method includes performing a first addition operation by using a first source internal key and an identifier (ID), the first source internal key being associated with the source device, the ID being associated with at least one of a target device and a storage medium of the target device, and the target device being connected to the source device; generating a source encryption key based on an output of the first addition operation and a second source internal key by using a predetermined encryption algorithm, wherein the second source internal key is associated with the source device; encrypting the digital content using the source encryption key; and transmitting the encrypted digital content without the source encryption key to the target device.