BESTIE: Broadcast Encryption Scheme for Tiny IoT Equipments

In public key broadcast encryption, anyone can securely transmit a message to a group of receivers such that privileged users can decrypt it. The three important parameters of the broadcast encryption scheme are the length of the ciphertext, the size of private/public key, and the performance of encryption/decryption. It is suggested to decrease them as much as possible, however, it turns out that decreasing one increases the other in most schemes. This paper proposes a new broadcast encryption scheme for tiny IoT equipments (BESTIE), minimizing the private key size in each user. In the proposed scheme, the private key size is O(log n), the public key size is O(log n), the encryption time per subset is O(log n), the decryption time is O(log n), and the ciphertext text size is O(r), where n denotes the maximum number of users and r indicates the number of revoked users. The proposed scheme is the first subset difference based broadcast encryption scheme to reduce the private size O(log n) without sacrificing the other parameters. We prove that our proposed scheme is secure under q-Simplified Multi-Exponent Bilinear Diffie-Hellman (q-SMEBDH) in the standard model

Theory and Applications of Outsider Anonymity in Broadcast Encryption

Broadcast Encryption (BE) allows efficient one-to-many secret communication of data over a broadcast channel. In the standard setting of BE, information about receivers is transmitted in the clear together with ciphertexts. This could be a serious violation of recipient privacy since the identities of the users authorized to access the secret content in certain broadcast scenarios are as sensitive as the content itself. Anonymous Broadcast Encryption (AnoBe) prevents this leakage of recipient identities from ciphertexts but at a cost of a linear lower bound (in the number of receivers) on the length of ciphertexts. A linear ciphertext length is a highly undesirable bottleneck in any large-scale broadcast application. In this thesis, we propose a less stringent yet very meaningful notion of anonymity for anonymous broadcast encryption called Outsider-Anonymous Broadcast Encryption (oABE) that allows the creation of ciphertexts that are sublinear in the number of receivers. We construct several oABE schemes with varying security guarantees and levels of efficiency. We also present two very interesting cryptographic applications afforded by the efficiency of our oABE schemes. The first is Broadcast Steganography (BS), the extension of the state of the art setting of point-to-point steganography to the multi-recipient setting. The second is Oblivious Group Storage (OGS), the introduction of fine-grained data access control policies to the setting of multi-client oblivious cloud storage protocols

Reducing Communication Overhead of the Subset Difference Scheme

In Broadcast Encryption (BE) systems like Pay-TV, AACS, online content sharing and broadcasting, reducing the header length (communication overhead per session) is of practical interest. The Subset Difference (SD) scheme due to Naor-Naor-Lotspiech (NNL) is the most popularly used BE scheme. We introduce the (a, b, γ) augmented binary tree subset difference ( (a, b, γ) -ABTSD) scheme which is a generalization of the NNL-SD scheme. By varying the parameters (a, b, γ) , it is possible to obtain O(n log n) different schemes. The average header length achieved by the new schemes is smaller than all known schemes having the same decryption time as that of the NNL-SD scheme and achieving non-trivial trade-offs between the user storage and the header size. The amount of key material that a user is required to store increases. For the earlier mentioned applications, reducing header size and achieving fast decryption is perhaps more of a concern than the user storage

Complete Tree Subset Difference Broadcast Encryption Scheme and its Analysis

The Subset Difference (SD) method proposed by Naor, Naor and Lotspiech is the most popular broadcast encryption (BE) scheme. It is suitable for real-time applications like Pay-TV and has been suggested for use by the AACS standard for digital rights management in Blu-Ray and HD-DVD discs. The SD method assumes the number of users to be a power of two. We propose the Complete Tree Subset Difference (CTSD) method that allows the system to support an arbitrary number of users. In particular, it subsumes the SD method and all results proved for the CTSD method also hold for the SD method. Recurrences are obtained for the CTSD scheme to count the number, $N(n,r,h)$, of possible ways $r$ users in the system of $n$ users can be revoked to result in a transmission overhead or header length of $h$. The recurrences lead to a polynomial time dynamic programming algorithm for computing $N(n,r,h)$. Further, they provide bounds on the maximum possible header length. A probabilistic analysis is performed to obtain an $O(r \log{n})$ time algorithm to compute the expected header length in the CTSD scheme. Further, for the SD scheme we obtain an explicit limiting upper bound on the expected header length

Tree based symmetric key broadcast encryption

The most influential broadcast encryption (BE) scheme till date was introduced in 2001 by Naor, Naor and Lotspiech (NNL) and is based on binary trees. This paper generalizes the ideas of NNL to obtain BE schemes based on k-ary trees for any k≥2. The treatment is uniform across all k and essentially provides a single scheme which is parameterized by the arity of the underlying tree. We perform an extensive analysis of the header length and user storage of the scheme. It is shown that for a k-ary tree with n users out of which r are revoked, the maximum header length is min(2r−1,n−r,⌈n/k⌉). An expression for the expected header length is obtained and it is shown that the expression can be evaluated in O(rlogn) time. Experimental results indicate that for values of r one would expect in applications such as pay TV systems, the average header length decreases as k increases. The number of keys to be stored by any user is shown to be at most (χk−2)ℓ0(ℓ0+1)/2, where ℓ0=⌈logkn⌉ and χk is the number of cyclotomic cosets modulo 2k−1. In particular, when the number of users is more than 1024, we prove that the user storage required for k=3 is less than that of k=2. For higher values of k, the user storage is greater than that for binary trees. The option of choosing the value of k provides a designer of a BE system with a wider range of trade-offs between average header length and user storage. The effect of layering on the k-ary tree SD scheme is also explored

Key management for wireless sensor network security

Wireless Sensor Networks (WSNs) have attracted great attention not only in industry but also in academia due to their enormous application potential and unique security challenges. A typical sensor network can be seen as a combination of a number of low-cost sensor nodes which have very limited computation and communication capability, memory space, and energy supply. The nodes are self-organized into a network to sense or monitor surrounding information in an unattended environment, while the self-organization property makes the networks vulnerable to various attacks.Many cryptographic mechanisms that solve network security problems rely directly on secure and efficient key management making key management a fundamental research topic in the field of WSNs security. Although key management for WSNs has been studied over the last years, the majority of the literature has focused on some assumed vulnerabilities along with corresponding countermeasures. Specific application, which is an important factor in determining the feasibility of the scheme, has been overlooked to a large extent in the existing literature.This thesis is an effort to develop a key management framework and specific schemes for WSNs by which different types of keys can be established and also can be distributed in a self-healing manner; explicit/ implicit authentication can be integrated according to the security requirements of expected applications. The proposed solutions would provide reliable and robust security infrastructure for facilitating secure communications in WSNs.There are five main parts in the thesis. In Part I, we begin with an introduction to the research background, problems definition and overview of existing solutions. From Part II to Part IV, we propose specific solutions, including purely Symmetric Key Cryptography based solutions, purely Public Key Cryptography based solutions, and a hybrid solution. While there is always a trade-off between security and performance, analysis and experimental results prove that each proposed solution can achieve the expected security aims with acceptable overheads for some specific applications. Finally, we recapitulate the main contribution of our work and identify future research directions in Part V

Engineering evaluations and studies. Volume 3: Exhibit C

High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed