Catálogo de publicaciones - libros

The concept of timed-released encryption with pre-open capability (TRE-PC) was introduced by Hwang, Yum and Lee. In a TRE-PC scheme, a message is encrypted in such a way that it can only be decrypted at a certain point in time or if the sender releases a piece of trapdoor information known as a pre-open key. This paper examines the security model for a TRE-PC scheme, demonstrates that a TRE-PC scheme can be constructed using a KEM–DEM approach, and provides an efficient example of a TRE-PC scheme.

In 2006, Huang, Susilo, Mu and Zhang proposed the concept of while Klonowski, Kubiak, Kutylowski and Lauks proposed independently the primitive of . In both notions, a signature holder can convince one or more verifiers of his knowledge of a digital signature, but cannot exploit this knowledge without being for that. In this paper, we state that a signature holder may generically provide a proof that it has a certain signature without being punished and that consequently both primitives cannot fulfill their alleged security goals. To demonstrate the feasibility of this claim, we propose the first non-interactive universal designated verifier proof of the possession of an Elgamal or a DSA signature in the random oracle model. This construction may be of independent interest.

A proxy re-encryption scheme allows Alice to temporarily delegate the decryption rights to Bob via a proxy. Alice gives the proxy a re-encryption key so that the proxy can convert a ciphertext for Alice into the ciphertext for Bob. In this paper, we propose two identity-based proxy re-encryption schemes, which are both proved secure in the standard model. The first one is efficient in both computation and ciphertext length, and the other one achieves chosen-ciphertext security. Our solutions answer the open problems left in the previous work.

We study the provable security of identity-based (ID-based) key agreement protocols. Although several published protocols have been proven secure in the random oracle model, only a weak adversarial model is considered – the adversary is not allowed to ask Session-KeyReveal queries that will allow the adversary to learn previously established session keys. Recent research efforts devoted to providing a stronger level of security require strong assumptions, such as assuming that the simulator has access to a non-existential computational or decisional oracle. In this work, we propose an ID-based key agreement protocol and prove its security in the widely accepted indistinguishability-based model of Canetti and Krawczyk. In our proof, the simulator does not require access to any non-existential computational or decisional oracle. We then extend our basic protocol to support ad-hoc anonymous key agreement with bilateral privacy. To the best of our knowledge, this is the first protocol of its kind as previously published protocols are for fixed group and provide only unilateral privacy (i.e., only one of the protocol participants enjoy anonymity).

We show in this paper that if the primes share their some bits (e.g. Least-Significant bits), RSA system with small private-exponent is much more vulnerable to the Boneh-Durfee Attack.

NLS is a stream cipher which was submitted to the eSTREAM project. A linear distinguishing attack against NLS was presented by Cho and Pieprzyk, which was called Crossword Puzzle (CP) attack. NLSv2 is a tweak version of NLS which aims mainly at avoiding the CP attack. In this paper, a new distinguishing attack against NLSv2 is presented. The attack exploits high correlation amongst neighboring bits of the cipher. The paper first shows that the modular addition preserves pairwise correlations as demonstrated by existence of linear approximations with large biases. Next, it shows how to combine these results with the existence of high correlation between bits 29 and 30 of the S-box to obtain a distinguisher whose bias is around 2. Consequently, we claim that NLSv2 is distinguishable from a random cipher after observing around 2 keystream words.

The stream ciphers Py, Py6 designed by Biham and Seberry were promising candidates in the ECRYPT-eSTREAM project because of their impressive speed. Since their publication in April 2005, a number of cryptanalytic weaknesses of the ciphers have been discovered. As a result, a strengthened version Pypy was developed to repair these weaknesses; it was included in the category of ‘Focus ciphers’ of the Phase II of the eSTREAM competition. However, even the new cipher Pypy was not free from flaws, resulting in a second redesign. This led to the generation of three new ciphers TPypy, TPy and TPy6. The designers claimed that TPy would be secure with a key size up to 256 bytes, i.e., 2048 bits. In February 2007, Sekar published an attack on TPy with 2 data and comparable time. This paper shows how to build a distinguisher with 2 key/IVs and one outputword per each key (i.e., the distinguisher can be constructed within the design specifications); it uses a different set of weak states of the TPy. Our results show that distinguishing attacks with complexity lower than the brute force exist if the key size of TPy is longer than 275 bits. Furthermore, we discover a large number of similar bias-producing states of TPy and provide a general framework to compute them. The attacks on TPy are also shown to be effective on Py.

In this paper, we study the performance of timeout-based queue management practices in the context of flood denial-of-service (DoS) attacks on connection-oriented protocols, where server resources are depleted by uncompleted illegitimate requests generated by the attacker. This includes both crippling DoS attacks where services become unavailable and Quality of Service (QoS) degradation attacks. While these queue management strategies were not initially designed for DoS attack protection purposes, they do have the desirable side-effect or providing some protection against them, since illegitimate requests time out more often than legitimate ones. While this fact is intuitive and well-known, very few quantitative results have been published on the potential impact on DoS-attack resilience of various queue management strategies and the associated configuration parameters. We report on the relative performance of various queue strategies under a varying range of attack rates and parameter configurations. We hope that such results will provide usable configuration guidelines for end-server or network appliance queue hardening. The use of such optimisation techniques is complementary to the upstream deployment of other types of DoS-protection countermeasures, and will probably prove most useful in scenarios where some residual attack traffic still bypasses them.

Program obfuscation is a semantic-preserving transformation aimed at bringing a program into such a form, which impedes the understanding of its algorithm and data structures or prevents extracting of some valuable information from the text of a program. Since obfuscation could find wide use in computer security, information hiding and cryptography, security requirements to program obfuscators became a major focus of interests for pioneers of theory of software obfuscation. In this paper we also address the issue of defining security of program obfuscation. We argue that requirements to obfuscation may be different and dependent on potential applications. Therefore, it makes sense to deal with a broad spectrum of security definitions for program obfuscation. In this paper we analyze five models for studying various aspects of obfuscation: “black box” model of total obfuscation, “grey box” model of total obfuscation, obfuscation for software protection, constant hiding, and predicate obfuscation. For each of these models we consider the applications where the model may be valid, positive and negative results on the existence of secure obfuscation in the framework of the model, and relationships with other models of program obfuscation.

An obfuscation aims to transform a program, without affecting the functionality, so that some secret information within the program can be hidden for as long as possible from an adversary. Proving that an obfuscating transform is correct ( it preserves functionality) is considered to be a challenging task.

In this paper we show how data refinement can be used to specify imperative data obfuscations. An advantage of this approach is that we can establish a framework in which we can prove the correctness of our obfuscations. We demonstrate our framework by considering some examples from obfuscation literature. We show how to specify these obfuscations, prove that they are correct and produce generalisations.