Accountable Attribute-Based Broadcast

In many broadcast applications, fine-grained access control over contents is required to provide differentiated services to users. For this purpose, the content provider may assign sets of attributes to the contents, and user access privileges are defined as logic expressions over these attributes. For example, in a digital video recorder (DVR) system, the content provider might broadcast episodes of TV shows and each of episode may be assigned a set of attributes such as name, season number, genre, so on and so forth. User access privileges can be encoded as policies such as (“name=friends” AND (“season 2” OR “season 3”)). To enforce these access polices, the content provider needs to encrypt the media products using some cryptographic primitives since the contents might be distributed across third party content delivery networks (CDNs). Key-policy attribute-based encryption (KP-ABE) [1] is a cryptographic primitive that was proposed to resolve the exact problem. In KP-ABE, a ciphertext is associated with a set of attributes, and each user secrete key is embedded with an access structure defined over attributes. Users can decrypt a ciphertext if and only if the attributes associated with the ciphertext satisfy the access structures embedded in their secret keys.