A broadcast encryption (BE) scheme is amethod for encryptingmessages in away that only a set of privileged users can decrypt it. Anonymity in a BE system is to hide any information on the privileged set. This problem has very recently had some attention and some constructions are proposed to achieve anonymity. However, anonymity in a trace and revoke (TR) scheme has not been studied yet, and to...

The most important point in the design of broadcast encryption schemes (BESs) is obtain a good trade-o between the amount of secret information that must be stored by every user and the length of the broadcast message, which are measured, respectively, by the information rate and the broadcast information rate B. In this paper we present a simple method to combine two given BESs in order to imp...

A revocation or a broadcast encryption technology allows a sender to transmit information securely over a broadcast channel to a select group of receivers excluding some revoked receivers. In this paper we propose two efficient revocation methods which are suitable for stateless receivers. The proposed methods use an a-ary key tree structure and

Broadcast encryption is the process of delivering encrypted data through a secure channel, intended for multiple users, in which only the privileged users can decrypt the content. In a broadcasting system, all the intended recipients are required to be accommodated in an organized way, which is possible through an efficient key management scheme. An ideal Broadcast Encryption scheme should defi...

We present a Hierarchical Identity Based Encryption (HIBE) system where the ciphertext consists of just three group elements and decryption requires only two bilinear map computations, regardless of the hierarchy depth. Encryption is as efficient as in other HIBE systems. We prove that the scheme is selective-ID secure in the standard model and fully secure in the random oracle model. Our syste...

Asymmetric group key agreement is a recently introduced versatile cryptographic primitive. It allows a group of users to negotiate a common encryption key which is accessible to any entities, and each user only holds her respective secret decryption key. This concept not only enables confidential communications among group users but also permits any outsider to send encrypted messages to the gr...

Traceability schemes for broadcast encryption are deened by Chor, Fiat and Naor in 6] to protect against a possible coalition of users producing an illegal decryption key. Their scheme was then generalized by Stinson and Wei in 17]. These schemes assume that every user can decrypt the secret value. In this paper we discuss key preassigned tra-cability schemes, in which only the users in a speci...

We present a new unifying framework for constructing non-interactive threshold encryption and signature schemes, as well as broadcast encryption schemes, and in particular, derive several new cryptosystems based on hardness of factoring, including: – a threshold signature scheme (in the random oracle model) that supports ad-hoc groups (i.e., exponential number of identities and the set-up is in...