Abstract: At the 1982 Symposium on Security and Privacy, a software protection scheme [1] devised by George Purdy, James Studier and the present author was presented. Unfortunately, the cryptographic protocol in that scheme was fatally flawed making it possible for a "pirate" who observed the communica-tions between a software vendor and a legitimate licensee to forge a license that would permit him to also use the protected software. In the course of analyzing the reasons for this weakness in the protocol and of finding an improved one, the cryptographic protocol reported here was found that permits the originator of a cipher message to specify precisely the subset of receivers out of a much larger potential audience who will be able to decrypt the cipher but who will be unable to pass along this ability to any other receiver not designated by the originator of the message. We shall first describe the flaw in the original software protection scheme that prompted this work, and then systematically develop the selective broadcast protocol . Finally, almost as a footnote to the discussion of the secure broadcast protocol, we show how the original software protection problem has also been solved.

Abstract: The idea of the Oblivious Transfer, developed by Rabin, has been shown to have important applications in cryptography. M. Fischer pointed out that Rabin's original implementation of the Oblivious Transfer was not shown to be secure. Since then it has been an open problem to find a provably secure implementation. We present an implementation which we believe will simplify the development of secure cryptographic protocols. Our protocol is provably secure under the assumptions that factoring is hard and that the message is chosen at random from a large message space.

Abstract: A problem with conflicting goals of anonymity and authentication is defined and a cryptographic protocol that solves the problem is presented. The protocol uses an authentication scheme that provides the desired degree of anonymity and authentication. Fake transactions are used to detect active attackers, and to camouflage information that cannot be hidden cryptographically.

Abstract: The Security of the RSA implementation of ping-pong protocols is considered. It is shown that the obvious RSA properties, such as “multiplicativity”, do not endanger the security of ping-pong protocols. Namely, if a ping-pong protocol is secure in general then its implementation using an “ideal RSA” is also secure.

Abstract: 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 Rabin'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 Mental 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.

Abstract: We develop a simple model of computation under which to study the meaning of cryptographic protocol and security. We define a protocol as a mathematical object and security as a possible property of this object, Having formalized the concept of a secure protocol we study its general properties. We back up our contention that the model is reasonable by solving some well known cryptography problems within the framework of the model.

Abstract: This paper presents a layered approach to the design of private key cryptographic algorithms based on a few strategically chosen layers. Each layer is a conceptually simple invertible transformation that may he weak in isolation, but makes a necessary contribution to the security of the algorithm. This is in contrast to algorithms such as DES which utilize many layers and depend on S-boxes that have no simple mathematical interpretation. A property called transparency is introduced to deal with the interaction of layers and how they must be selected to eliminate system weaknesses.Utilizing this layered approach, a private key cryptographic algorithm consisting of three layers is constructed to demonstrate the design criteria. The algorithm has an adequate key space and valid keys can be easily generated. The design is based on a symmetrical layered configuration, which allows encryption and decryption to be performed using the same algorithm. The algorithm is suitable for VISI implementation. Some statistical tests are applied to the algorithm in order that its cryptographic performance can be evaluated. The test results and attempts at cryptanalysis suggest that the three-layered algorithm is secure.

Abstract: In the paper, application of idempotent elements to construction of cryptographic systems has been presented. The public key cryptosystem based on idempotent elements and the cryptographic transformation that preserves elementary arithmetic operations have been described.

Abstract: A cryptographic scheme for controlling access to information within a group of users organized in a hierarchy was proposed in [1]. The scheme enables a user at some level to compute from his own cryptographic key the keys of the users below him in the organization.