Asiacrypt 2011 Day 2

The first talk at Asiacrypt day 2 is the talk on "Bridging brocast encryption and group key agreement". The work bridges two well-studied primitives, broadcast encryption and group key agreement, with a new hybrid primitive referred to as contributory brocadast encryption (CBE). In CBE, a group of members contribute to the public group encryption key. A sender can securely broadcast to any subset of the group members which is chosen in an ad hoc way. CBE incorporates the ideas of broadcast encryption and group key agreement. In the set-up phase, a group of members interact via open networks to negotiate a common encryption key while each member keeps a different secret decryption key. Anyone can necrypt message to any subset of the group members by using the common encryption key and only the intended receiver can decrypt the ciphertext. CBE allows the sender to exclude some group members from reading the ciphertext (compared to group key agreement) and does not need a fully trusted third party to set up the system (compared to broadcast encryption). Finally, a CBE construction proven to be semi-adaptively secure under decision BDHE assumption in the standard model is also proposed.