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Broadcast encryption was introduced by Fiat and Naor in 1993, In a broadcast encryption scheme a broadcaster encrypts a message for some subset S of users who are listening on a broadcast channel. A user in S can use his private key to decrypt the broadcast. Any user outside the privileged set S should not be able to recover the message. Recently it has been widely used in digital rights management applications such as pay-TV, multicast communication and DVD content protection. Although the broadcast encryption technology is more and more perfect, we need to discuss special schemes in special application environment, and we need to improve its computing efficient and storing efficient.This study is divided into two parts, first introduced the broadcast encryption technology overview, introduced the symmetric key broadcast encryption scheme and public key broadcast encryption scheme, then, According to the new application background, we proposed the concept of dynamic broadcast encryption, and achieve the following results:(1) We improve DPP07 and propose a scheme that reduces ek size and encryption cost, In DPP07, the published encryption key ekcontains n elements over GT,in this scheme we set a dummy decryption key in ek, so that when the sender want to compute SK, its cost is only O(l) while in DPP scheme it is O(r).(2) By improve the aggregate function, we design a more efficient dynamic broadcast encryption, in DDP scheme, key agreement is based on G, however, in this scheme, we compute session key based on G.obviously, G’s computing cost is O(r), and G’s computing cost is O(r2), so we make the encryption and decryption computation more efficient.
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