Content from both the NLS and the Learning Ally organizations uses the "DAISY Protected Digital Book" ("PDTB") encryption standard. The basic structure of the DAISY definition files remains the same, however, the audio itself, and in some cases certain information tags in the DAISY SMIL files, are encrypted and must be decrypted in order to be read/played back. The organization which offers the content provides a decryption key to the user, which can be installed into a DAISY player to allow decryption. As the encryption schemes are not part of the core DAISY standard, only players which specifically implement the necessary algorithms and key management will be able to access these titles. Bookshare utilizes its own digital rights management plan including fingerprinting each digital book with the identity of the downloading user. These actions are done to comply with law 17 U.S.C. § 121 requiring copyrighted material to be distributed in a specialized format to prevent unauthorized individuals, such as those who do not have a qualifying disability, from accessing the materials.