From the Publisher:
A valuable reference for the novice as well as for the expert who needs a wider scope of coverage within the area of cryptography, this book provides easy and rapid access of information and includes more than 200 algorithms and protocols; more than 200 tables and figures; more than 1,000 numbered definitions, facts, examples, notes, and remarks; and over 1,250 significant references, including brief comments on each paper.

Handbook of Applied Cryptography

A network-based sales system includes at least one buyer computer for operation by a user desiring to buy a product, at least one merchant computer, and at least one payment computer. The buyer computer, the merchant computer, and the payment computer are interconnected by a computer network. The buyer computer is programmed to receive a user request for purchasing a product, and to cause a payment message to be sent to the payment computer that comprises a product identifier identifying the product. The payment computer is programmed to receive the payment message, to cause an access message to be created that comprises the product identifier and an access message authenticator based on a cryptographic key, and to cause the access message to be sent to the merchant computer. The merchant computer is programmed to receive the access message, to verify the access message authenticator to ensure that the access message authenticator was created using the cryptographic key, and to cause the product to be sent to the user desiring to buy the product.

Network sales system

Informally, an obfuscator O is an (efficient, probabilistic) "compiler" that takes as input a program (or circuit) P and produces a new program O(P) that has the same functionality as P yet is "unintelligible" in some sense. Obfuscators, if they exist, would have a wide variety of cryptographic and complexity-theoretic applications, ranging from software protection to homomorphic encryption to complexity-theoretic analogues of Rice's theorem. Most of these applications are based on an interpretation of the "unintelligibility" condition in obfuscation as meaning that O(P) is a "virtual black box," in the sense that anything one can efficiently compute given O(P), one could also efficiently compute given oracle access to P.

In this work, we initiate a theoretical investigation of obfuscation. Our main result is that, even under very weak formalizations of the above intuition, obfuscation is impossible. We prove this by constructing a family of functions F that are inherently unobfuscatable in the following sense: there is a property π : F → {0, 1} such that (a) given any program that computes a function f ∈ F, the value π(f) can be efficiently computed, yet (b) given oracle access to a (randomly selected) function f ∈ F, no efficient algorithm can compute π(f) much better than random guessing. We extend our impossibility result in a number of ways, including even obfuscators that (a) are not necessarily computable in polynomial time, (b) only approximately preserve the functionality, and (c) only need to work for very restricted models of computation (TC0). We also rule out several potential applications of obfuscators, by constructing "unobfuscatable" signature schemes, encryption schemes, and pseudorandom function families.

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On the (Im)possibility of Obfuscating Programs

This invention relates to methods for controlling and monitoring access to network servers. In particular, the process described in the invention includes client-server sessions over the Internet. In this environment, when the user attempts to access an access-controlled file, the server subjects the request to a secondary server which determines whether the client has an authorization or valid account. Upon such verification, the user is provided with a session identification which allows the user to access to the requested file as well as any other files within the present protection domain.

Internet server access control and monitoring systems

An electronic-monetary system having (1) banks or financial institutions that are coupled to a money generator device for generating and issuing to subscribing customers electronic money including electronic currency backed by demand deposits and electronic credit authorizations; (2) correspondent banks that accept and distribute the electronic money; (3) a plurality of transaction devices that are used by subscribers for storing electronic money, for performing money transactions with the on-line systems of the participating banks or for exchanging electronic money with other like transaction devices in off-line transactions; (4) teller devices, associated with the issuing and correspondent banks, for process handling and interfacing the transaction devices to the issuing and correspondent banks, and for interfacing between the issuing and correspondent banks themselves; (5) a clearing bank for balancing the electronic money accounts of the different issuing banks; (6) a data communications network for providing communications services to all components of the system; and (7) a security arrangement for maintaining the integrity of the system, and for detecting counterfeiting and tampering within the system. An embodiment of the invention includes a customer service module which handles lost money claims and links accounts to money modules for providing bank access.

Electronic monetary system

A “promise problem” is a formulation of partial decision problem. Complexity issues about promise problems arise from considerations about cracking problems for public-key cryptosystems. Using a notion of Turing reducibility between promise problems, this paper disproves a conjecture made by Even and Yacobi (1980) , that would imply nonexistence of public-key cryptosystems with NP-hard cracking problems. In its place a new conjecture is raised having the same consequence. In addition, the new conjecture implies that NP-complete sets cannot be accepted by Turing machines that have at most one accepting computation for each input word.

The complexity of promise problems with applications to public-key cryptography

Apparatus for effecting and recording monetary transac- tons including apparatus for registering the present value of money therein, apparatus for selectably adjusting the registered value to indicate a payment and receipt transaction, and identity verification apparatus including asymmetric cryptographic apparatus coupled to the apparatus for adjusting for activation thereof. The apparatus as a whole is provided as an electronic wallet (10) comprising a display (12), a keyboard (14) and a connecting jack (16).

An apparatus for effecting and recording monetary transactions

In view of the known difficulty in solving NP-hard problems, a natural question is whether there exist cryptosystems which are NP-hard to crack. In Section I we display two such systems which are based on the knapsack problem. However, the first one, which is highly "linear" has been shown by Lempel to be almost always easy to crack. This shows that NP-hardness of a cryptosystem is not enough. Also, it provides the only natural problem we know of, which is NP-hard and yet almost always easy to solve. The second system is a form of a "double knapsack" and so far has resisted the cryptanalysis efforts.

Cryptocomplexity and NP-Completeness

Nancy Lynch proved that if a decision problem A is not solvable in polynomial time, then there exists an infinite recursive subset X of its domain on which the decision is almost everywhere complex. In this paper, general theorems of this kind that can be applied to several well-known automata-based complexity classes, including a common class of randomized algorithms, are proved.

Hard-core theorems for complexity classes

A “promise problem” is a formulation of a partial decision problem. Complexity issues about promise problems arise from Even and Yacobi's work in public-key cryptography

Yacov Yacobi

Papers

The complexity of promise problems with applications to public-key cryptography

An apparatus for effecting and recording monetary transactions

Cryptocomplexity and NP-Completeness

Hard-core theorems for complexity classes

The Complexity of Promise Problems