Hiding the Policy in Cryptographic Access Control

Recently, cryptographic access control has received a lot of attention, mainly due to the availability of efficient Attribute-Based Encryption (ABE) schemes. ABE allows to get rid of a trusted reference monitor by enforcing access rules in a cryptographic way. However, ABE has a privacy problem: the access policies are sent in clear along with the ciphertexts. Further generalizing the idea of policy-hiding in cryptographic access control, the authors introduce policy anonymity where - similar to the well-understood concept of k-anonymity - the attacker can only see a large set of possible policies that might have been used to encrypt, but is not able to identify the one that was actually used.