Browsing by Author "Ak, Murat"

Now showing 1 - 3 of 3

Open Access
Generic construction of trace and revoke schemes
(2012) Ak, Murat; Kiayias, A.; Pehlivanoğlu, S.; Selçuk, Ali Aydın
Open Access
Optimal broadcasting encryption with free riders
(2006) Ak, Murat
Broadcast encryption schemes allow a center to broadcast encrypted messages so that each particular message can only be decrypted by a set of privileged receivers designated for it. The standard technique is to distribute keys to all receivers at the beginning and to use only the necessary keys to encrypt the message for each particular broadcast. The number of encryptions needed constitutes the transmission cost in broadcast encryption schemes. The most efficient scheme in terms of transmission cost published so far is the subset difference (SD) scheme. It is possible to reduce the transmission overhead of a broadcast encryption scheme by allowing a number of free riders to be able to decrypt the message although they are not privileged. However, unless the free riders are chosen cleverly, the cost may even increase. In this thesis, we deal with the problem of choosing a given number of free riders effectively to reduce the transmission overhead in SD scheme. We first present three greedy algorithms. First algorithm has a fast execution, the second one is slower but has lower transmission overhead, and the last one has a trade-off between running time and transmission cost. Then we present two algorithms which find the minimum transmission overhead possible given a free rider quota. The experiments we conduct show that the transmission cost can be significantly reduced.
Open Access
Optimization techniques and new methods for boradcast encryption and traitor tracing schemes
(2012) Ak, Murat
In the last few decades, the use of digital content increased dramatically. Many forms of digital products in the form of CDs, DVDs, TV broadcasts, data over the Internet, entered our life. Classical cryptography, where encryption is done for only one recipient, was not able to handle this change, since its direct use leads to intolerably expensive transmissions. Moreover, new concerns regarding the commercial aspect arised. Since digital commercial contents are sold to various customers, unauthorized copying by malicious actors became a major concern and it needed to be prevented carefully. Therefore, a new research area called digital rights management (DRM) has emerged. Within the scope of DRM, new cryptographic primitives are proposed. In this thesis, we consider three of these: broadcast encryption (BE), traitor tracing (TT), and trace and revoke (T&R) schemes and propose methods to improve the performances and capabilities of these primitives. Particularly, we first consider profiling the recipient set in order to improve transmission size in the most popular BE schemes. We then investigate and solve the optimal free rider assignment problem for one of the most efficient BE schemes so far. Next, we attempt to close the non-trivial gap between BE and T&R schemes by proposing a generic method for adding traitor tracing capability to BE schemes and thus obtaining a T&R scheme. Finally, we investigate an overlooked problem: privacy of the recipient set in T&R schemes. Right now, most schemes do not keep the recipient set anonymous, and everybody can see who received a particular content. As a generic solution to this problem, we propose a method for obtaining anonymous T&R scheme by using anonymous BE schemes as a primitive.