Public-Key Revocation and Tracing Schemes with Subset Difference Methods Revisited

Trace and revoke is broadcast encryption with the traitor tracing functionality. It is a very powerful primitive since it can revoke users whose private keys are compromised by finding them using a tracing algorithm if a pirate decoder is given. Public-key trace and revoke (PKTR) is a special type of trace and revoke such that anyone can run the tracing algorithm and anyone can create an encrypted message by using a public key. Although public-key trace and revoke schemes are attractive tools, the currently known PKTR schemes are a little bit inefficient in terms of the private key size and the public key size compared with public-key broadcast encryption schemes. In this paper, we propose a new technique to construct an efficient PKTR scheme by using the subset cover framework. First, we introduce a new concept of public-key encryption named single revocation encryption (SRE) and propose an efficient SRE scheme in the random oracle model. The universe of SRE consists of many groups and each group consists of many members. A user in SRE is represented as a group that he belongs and a member in the group. In SRE, a sender can create a ciphertext for a specified group where one member in the group is revoked, and a receiver can decrypt the ciphertext if he belongs to the group in the ciphertext and he is not revoked in the group. Second, we show that the subset difference (SD) scheme (or the layered subset difference (LSD) scheme) and a SRE scheme can be combined to construct a PKTR scheme. Our PKTR scheme using the LSD scheme and our SRE scheme has the ciphertext size of $O(r)$, the private key size of $O(\log^{1.5} N)$, and the public key size of $O(1)$ where $N$ is the total number of users in the system and $r$ is the size of a revoked set. Our PKTR scheme is the first one that achieves the private key size of $O(\log^{1.5} N)$ and the public key size of $O(1)$

A Security Analysis of Some Physical Content Distribution Systems

Content distribution systems are essentially content protection systems that protect premium multimedia content from being illegally distributed. Physical content distribution systems form a subset of content distribution systems with which the content is distributed via physical media such as CDs, Blu-ray discs, etc. This thesis studies physical content distribution systems. Specifically, we concentrate our study on the design and analysis of three key components of the system: broadcast encryption for stateless receivers, mutual authentication with key agreement, and traitor tracing. The context in which we study these components is the Advanced Access Content System (AACS). We identify weaknesses present in AACS, and we also propose improvements to make the original system more secure, flexible and efficient

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

Automating Fast and Secure Translations from Type-I to Type-III Pairing Schemes

Pairing-based cryptography has exploded over the last decade, as this algebraic setting offers good functionality and efficiency. However, there is a huge security gap between how schemes are usually analyzed in the academic literature and how they are typically implemented. The issue at play is that there exist multiple types of pairings: Type-I called “symmetric” is typically how schemes are presented and proven secure in the literature, because it is simpler and the complexity assumptions can be weaker; however, Type-III called “asymmetric” is typically the most efficient choice for an implementation in terms of bandwidth and computation time. There are two main complexities when moving from one pairing type to another. First, the change in algebraic setting invalidates the original security proof. Second, there are usually multiple (possibly thousands) of ways to translate from a Type-I to a Type-III scheme, and the “best” translation may depend on the application. Our contribution is the design, development and evaluation of a new software tool, AutoGroup+, that automatically translates from Type-I to Type-III pairings. The output of AutoGroup+ is: (1) “secure” provided the input is “secure” and (2) optimal based on the user’s efficiency constraints (excluding software and run-time errors). Prior automation work for pairings was either not guaranteed to be secure or only partially automated and impractically slow. This work addresses the pairing security gap by realizing a fast and secure translation tool

Attribute Based Encryption for Secure Data Access in Cloud

Cloud computing is a progressive computing worldview, which empowers adaptable, on-request, and ease use of Information Technology assets. However, the information transmitted to some cloud servers, and various protection concerns are arising out of it. Different plans given the property-based encryption have been proposed to secure the Cloud Storage. In any case, most work spotlights on the information substance security and the get to control, while less consideration towards the benefit control and the character protection. In this paper, a semi-anonymous benefit control conspires AnonyControl to address the information protection, as well as the client character security in existing access control plans. AnonyControl decentralizes the central authority to restrain the character spillage and accordingly accomplishes semi-anonymity. Furthermore, it likewise sums up the document get to control to the benefit control, by which advantages of all operations on the cloud information managed in a fine-grained way. Along these lines, display the AnonyControl-F, which ultimately keeps the character spillage and accomplish the full secrecy. Our security assessment demonstrates that both AnonyControl and AnonyControl-F are secure under the decisional bilinear Diffie-Hellman presumption, and our execution assessment shows the attainability of our plans. Index Terms: Anonymity, multi-authority, attribute-based encryption

HUC-HISF: A Hybrid Intelligent Security Framework for Human-centric Ubiquitous Computing

制度:新 ; 報告番号:乙2336号 ; 学位の種類:博士(人間科学) ; 授与年月日:2012/1/18 ; 早大学位記番号:新584

Ciphertext-Policy Attribute-Based Encryption with Key-Delegation Abuse Resistance

Attribute-based encryption (ABE) is a promising cryptographic primitive that allows one-to-many encryption. In such a system, users\u27 private keys are linked to their access rights. We note that if a user can generate a new private key for a portion of his/her access right, this could potentially lead to some undesirable situations, which violate the access control policy. Interestingly, to date, there is no work that looks into this matter in detail nor addresses it. We point out that this is a property that exists in ABE systems, which we refer to key-delegation abuse . ABE systems that suffer from key-delegation abuse will hinder the adoption of these systems in practice. In this work, for the first time in the literature, we address the key-delegation abuse problem in Ciphertext-policy Attribute-based Encryption (CP-ABE) systems. We introduce a new mechanism to enhance CP-ABE schemes that provide protections against this key-delegation abuse issue. We formalize the security requirements for such a property, and subsequently construct a CP-ABE scheme that satisfies the new security requirements. We also present an application of our scheme to a traceable CP-ABE, where the traitors , i.e. the users who have leaked their keys, can be traced. address the key-delegation abuse problem in Ciphertext-policy Attribute-based Encryption (CP-ABE) systems. We introduce a new mechanism to enhance CPABE schemes that provide protections against this key-delegation abuse issue. We formalize the security requirements for such a property, and subsequently construct a CP-ABE scheme that satisfies the new security requirements.We also present an application of our scheme to a traceable CP-ABE, where the traitors , i.e. the users who have leaked their keys, can be traced

IST Austria Thesis

Many security definitions come in two flavors: a stronger “adaptive” flavor, where the adversary can arbitrarily make various choices during the course of the attack, and a weaker “selective” flavor where the adversary must commit to some or all of their choices a-priori. For example, in the context of identity-based encryption, selective security requires the adversary to decide on the identity of the attacked party at the very beginning of the game whereas adaptive security allows the attacker to first see the master public key and some secret keys before making this choice. Often, it appears to be much easier to achieve selective security than it is to achieve adaptive security. A series of several recent works shows how to cleverly achieve adaptive security in several such scenarios including generalized selective decryption [Pan07][FJP15], constrained PRFs [FKPR14], and Yao’s garbled circuits [JW16]. Although the above works expressed vague intuition that they share a common technique, the connection was never made precise. In this work we present a new framework (published at Crypto ’17 [JKK+17a]) that connects all of these works and allows us to present them in a unified and simplified fashion. Having the framework in place, we show how to achieve adaptive security for proxy re-encryption schemes (published at PKC ’19 [FKKP19]) and provide the first adaptive security proofs for continuous group key agreement protocols (published at S&P ’21 [KPW+21]). Questioning optimality of our framework, we then show that currently used proof techniques cannot lead to significantly better security guarantees for "graph-building" games (published at TCC ’21 [KKPW21a]). These games cover generalized selective decryption, as well as the security of prominent constructions for constrained PRFs, continuous group key agreement, and proxy re-encryption. Finally, we revisit the adaptive security of Yao’s garbled circuits and extend the analysis of Jafargholi and Wichs in two directions: While they prove adaptive security only for a modified construction with increased online complexity, we provide the first positive results for the original construction by Yao (published at TCC ’21 [KKP21a]). On the negative side, we prove that the results of Jafargholi and Wichs are essentially optimal by showing that no black-box reduction can provide a significantly better security bound (published at Crypto ’21 [KKPW21c])