AO File

What are AO files and how to open them

Are you having problems opening an AO file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your AO files.

What is an AO file?

An .AO file is a DAISY Authorization Object file.

The DAISY Authorization Object is an XML-based file that carries encrypted rights and decryption keys for a specific digital book produced under DAISY's Protected Digital Talking Book (PDTB) system. It is issued by an authorizing party (e.g. publisher or library), tied to one particular book, and is meant to be used by reading systems to verify permissions and unlock encrypted content.

This file is created during the protection workflow for a DAISY DTB. The issuer encrypts the book's media (text, audio, images) and generates decryption keys; those keys plus a rights-expression (for how content may be used) are placed into the authorization object and itself encrypted under one or more authorization keys known to compatible reading systems. When a user attempts to open the protected book, the reading system checks whether it holds one of the authorization keys referenced, then decrypts the rights expression and the content decryption keys so it can render the content.

Inside this file are well-defined XML elements such as BookAuthorization (the root element defined by the schema AuthObj.xsd), Issuer, Book (with a uid matching the book's identifier), Rights (an ODRL rights expression), Keys (containing one or more ContentKey entries for different media types), EncryptedRights (an encrypted version of Rights), EncryptedKey, EncryptedData, KeyInfo, CarriedKeyName, EncryptionMethod, CipherData/CipherValue, and others. The namespace used is typically "http://www.daisy.org/DRM/2005/BookAuthorization".

A technical identifier unique to this format is that the file begins with the ASCII string "<?xml version="1.0"" at offset zero. It contains the string "BOOKAUTHORIZATION AUTHOBJ.XSD" along with tags like ENCRYPTEDDATA TYPE, CONTENTKEY MEDIA, ENCRYPTEDRIGHTS, CARRIEDKEYNAME, ENCRYPTEDKEY, KEYINFO, XMLDSIG, XMLENC, and so on, all of which indicate its role in transmitting rights and decryption keys under DAISY's encryption spec. (Keywords are case-insensitive; strings shown in evidence.)

How to open AO files

Important: Different programs may use files with the AO file extension for different purposes, so unless you are sure which format your AO file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested three different AO openers which you will find listed below.

Last updated: August 18, 2026

Various apps that use files with this extension

These apps are known to open certain types of AO files. Remember, different programs may use AO files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about AO file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.