Investigating the capabilities of public key and related cryptographic techniques has recently become an important area of cryptographic research. In this paper we present some new algorithms and cryptographic protocols (Cryptoprotocols) which enlarge the range of applications of public key systems and enable us to perform certain transactions in communication networks. The basic cryptographic tools used are Rabm's Oblivious Transfer Protocol and an algorithm we developed for Number Embedding which is provably hard to invert. We introduce the protocol Subscription to a Public Key, which gives a way to transfer keys over insecure communication channels and has useful applications to cryptosystems. We develop the Secret Blocking Protocol, specified as follows 'A transfers a secret to B, B can block the message. If B does not block it, there is a probability P that he might get it. (1/2 ≤ P < 1, where we can control the size of P). A does not know if the message was blocked (but he can find out later)'. The classic cryptotransaction is the A1ental Poker Game. A cryptographically secure solution to the Multi Player Mental Poker Game is given. The approach used in constructing the solution provides a general methodology of provable and modular Protocol Composition.
Investigating the capabilities of public key and related cryptographic techniques has recently become an important area of cryptographic research. In this paper we present some new algorithms and cryptographic protocols (Cryptoprotocols) which enlarge the range of applications of public key systems and enable us to perform certain transactions in communication networks. The basic cryptographic tools used are Rabm's Oblivious Transfer Protocol and an algorithm we developed for Number Embedding which is provably hard to invert. We introduce the protocol Subscription to a Public Key, which gives a way to transfer keys over insecure communication channels and has useful applications to cryptosystems. We develop the Secret Blocking Protocol, specified as follows 'A transfers a secret to B, B can block the message. If B does not block it, there is a probability P that he might get it. (1/2 ≤ P < 1, where we can control the size of P). A does not know if the message was blocked (but he can find out later)'. The classic cryptotransaction is the A1ental Poker Game. A cryptographically secure solution to the Multi Player Mental Poker Game is given. The approach used in constructing the solution provides a general methodology of provable and modular Protocol Composition.
Over the past four decades, computational power and algorithmic strategies have advanced tremendously resulting in an enormous increase in the key sizes required for secure cryptosystems such as RSA. At the same time, the electronic devices have grown smaller and portable requiring algorithms running on them to be optimized in size and efficiency while providing security, at least, equivalent to that provided on a typical desktop computer. As a result, the industry is moving towards newer cryptosystems such as ECC and NTRU that are well suited for resource constrained environments. While, ECC claims to provide security equivalent to that of RSA for a fraction of key size, NTRU is inherently suited for embedded systems technology. However, implementation of new cryptosystems requires the development of protocols analogous to those developed using older cryptosystems. In this thesis, we fulfill a part of this requirement by providing protocols for Oblivious Transfer using ECC and NTRU. Oblivious Transfer, in turn, has applications in simultaneous contract signing, digital certified mail, simultaneous exchange of secrets, secure multiparty computations, private information retrieval, etc. Furthermore, we introduce the idea of basing Oblivious Transfer on public-key exchange protocols. The presentation in the thesis uses Diffie-Hellman Key Exchange, but the scheme is generalizable to any cryptosystem that has a public-key exchange strategy. In fact, our proposal may especially be suited for Quantum Cryptography where the security of key exchange protocols has been proven.
An efficient and secure mental poker scheme is proposed in this paper. It is based on multiple encryption and decryption of individual cards. The protocol satisfies all major security requirements of a real mental poker. It gets rid of the Card Salesman and guarantees minimal effect due to collusion of players. The protocol is secure and more efficient compared with other known protocols. The strategies of players can be kept confidential with the introduction of a Dealer. The protocol is suitable to be implemented in an on-line card game.
This paper summarizes the current knowledge in the field of two-party cryptographic protocols devised from quantum systems. We introduce the reader to the notion of cryptographic protocols and describe a number of simple building blocks to achieve them. We also give pointers for the reader who is interested to the quantum implementation of these building blocks. 1 Introduction Since the 1970's the science of secret writing, cryptography, has changed substantially due to the introduction of "public key cryptosystems" [26, 41]. The many properties of certain instances of these systems have open the door to several new applications (consult [42, 25, 29, 44, 34, 28, 7, 30, 36, 32, 11, 19, 33] for instance, to mention just a few). The initial goal of cryptography, to provide secure communications, has evolved into a variety of tasks involving secret data. The scenario in which such tasks take place involves two participants (say Alice and Bob) who wish to perform some computation involving ...
This thesis considers cryptographic systems that use public key encryption (PKE) as a building block in a larger system. We call these cryptosystems and develop a framework for describing such protocols that provides a clear way of describing the role of PKE in the PKE-hybrid protocol. By clarifying and generalizing the role of PKE in such protocols, we are able to state and prove a powerful lemma for proving the security of PK-hybrid protocols. We then show how this lemma can be used in a proof of security for the standard technique of hybrid encryption, substantially simplifying earlier proofs by Cramer and Shoup and by Abe, et al. In addressing these protocols we make improvements to a previously published protocol for Generalized Non-Interactive Oblivious Transfer (GNIOT) due to Gunupudi and Tate, and use our new security framework to correct a subtle error in the original security proof provided for GNIOT.
As traditional oblivious transfer protocols are treated as a cryptographic primitive, they are usually executed without the consideration of possible attacks, e.g., impersonation, replaying, and man-in-the-middle attacks. Therefore, when these protocols are applied in certain applications such as mental poker playing, some necessary mechanism must be executed first to ensure the security of subsequent communications. But doing this way, we found that almost all of the resulting mechanisms are not efficient enough in communicational cost which is a significant concern for commercial transactions. Inspired by these observations, we propose a novel secure oblivious transfer protocol based on bilinear pairing which not only can provide mutual authentication to resist malicious attacks but also is efficient in communicational cost, other than its original functions. Keywords: oblivious transfer, mutual authentication, ID-based cryptosystem, bilinear
Mental card games are played without a trusted party and without cards. It is well known that the problem of mental card games can be solved in principle. But the schemes known so far are too messy to be used in practice. Only for the mental poker game a suitable solution is known [Cr'ep 87] that achieves security against player coalition and complete confidentiality of a player's strategy. Here, we present a general-purpose scheme that may be used as basic toolbox for straight-forward implementations of card games. We present a data structure for cards and decks that is secure against player coalitions and enables standard operations like picking up a card, opening it, and (re-)mixing stacks. Futhermore, we introduce tools for special operations like inserting a card into the deck, splitting the deck, parting the game. The correctness of all operations is testified by zeroknowledge proofs. Finally, we discuss security problems that are typical for mental card games and suggest solutio...