Copyright protection is a major issue in distributing digital content. On the other hand, improvements to usability are sought by content users. In this paper, we propose a secure {\it traitor ...tracing scheme against key exposure (TTaKE)} which contains the properties of both a traitor tracing scheme and a forward secure public key cryptosystem. Its structure fits current digital broadcasting systems and it may be useful in preventing traitors from making illegal decoders and in minimizing the damage from accidental key exposure. It can improve usability through these properties.
In this paper, we present a new public key encryption scheme which is proven chosen-ciphertext (CCA) secure under the decisional Diffie-Hellman (DDH) assumption. The main motivation behind this ...scheme is to clarify the essential mechanism for yielding CCA-security from the DDH assumption. The structure and security proof of our scheme is simple, and it is likely that even non-experts can immediately understand them with ease. We consider that our scheme is helpful for convincing a wide range of users (including developers and students who are just starting to study CCA-secure encryption) how the Cramer-Shoup cryptosystem and its variants work.
Copyright protection is a major issue in distributing digital content. On the other hand, improvements to usability are sought by content users. In this paper, we propose a secure traitor tracing ...scheme against key exposure (TTaKE) which contains the properties of both a traitor tracing scheme and a forward secure public key cryptosystem. Its structure fits current digital broadcasting systems and it may be useful in preventing traitors from making illegal decoders and in minimizing the damage from accidental key exposure. It can improve usability through these properties
In this work we propose a Deniable Ring Authentication scheme secure against a powerful Big Brother type of adversary and yielding an optimal number of communication rounds. Our scheme is based on an ...infra-structure assumption: the existence of verifiable Broadcast Encryption. Particularly, our solution can be instantiated by using the Broadcast Encryption protocol of Boneh, Gentry and Waters (CRYPTO 2005), resulting in a Deniable Ring Authentication protocol with constant message size.
Unforgeability of digital signatures is closely related to the security of hash functions since hashing messages, such as hash-and-sign paradigm, is necessary in order to sign (arbitrarily) long ...messages. Recent successful collision finding attacks against practical hash functions would indicate that constructing practical collision resistant hash functions is difficult to achieve. Thus, it is worth considering to relax the requirement of collision resistance for hash functions that is used to hash messages in signature schemes. Currently, the most efficient strongly unforgeable signature scheme in the standard model which is based on the CDH assumption (in bilinear groups) is the Boneh-Shen-Waters (BSW) signature proposed in 2006. In their scheme, however, a collision resistant hash function is necessary to prove its security. In this paper, we construct a signature scheme which has the same properties as the BSW scheme but does not rely on collision resistant hash functions. Instead, we use a target collision resistant hash function, which is a strictly weaker primitive than a collision resistant hash function. Our scheme is, in terms of the signature size and the computational cost, as efficient as the BSW scheme.
Summary form only given. We discuss information-theoretic methods to prove the security of cryptosystems. We study what is called, unconditionally secure (or information-theoretically secure) ...cryptographic schemes in search for a system that can provide long-term security and that does not impose limits on the adversary's computational power.
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