Presents an architecture for the efficient encoding of Reed-Solomon codes, with or without interleaving. This architecture utilizes a clock whose rate is r times the symbol rate, where r is the redundancy of the code. The finite field operations are performed in a sequential manner, requiring only one finite field multiplier and one finite field adder. All memory elements (except one symbol register) are consolidated into a discrete-time delay line, which can be easily implemented with a random access memory. This approach alleviates the clock skew problem and leads to significant hardware savings over the usual parallel approach, when the redundancy and/or interleaving depth are large. The architecture can be easily reconfigured for changes in the generator polynomial of the code, the amount of redundancy, and the interleaving depth.>

A seven-chip set which performs the functions associated with video and image compression algorithms, and CCITT H.261 in particular, has been designed, fabricated, and is fully functional. The major functions performed by the devices include motion estimation, DCT and IDCT, forward and inverse quantization, Huffman coding and decoding, BCH error correction, and loop filtering. The chips that perform the predictive and transform coding section of the algorithm operate with pixel rates up to 40 MHz. Array-based technologies of 1.5 and 1.0 mu m CMOS were used extensively to achieve a 28 man-month design time. Each die is less than 10 mm on a side.>

Abstract Let G(V, E) be an undirected graph which describes the structure of a communication network. During the maintenance period every line must be tested in each of the two possible directions. A line is tested by assigning one of its endpoints to be a transmitter, the other to be a receiver, and sending a message from the transmitter to the receiver through the line. We define several different models for communication networks, all subject to the two following axioms: a vertex cannot act as a transmitter and as a receiver simultaneously and a vertex cannot receive through two lines simultaneously. In each of the models, two problems arise: What is the maximum number of lines one can test simultaneously? and What is the minimum number of phases necessary for testing the entire network?, where, by “phase” we mean a period in which some tests are conducted simultaneously. We show that in most models, including the “natural” model of radio communication, both problems are NP‐hard. In some models the problems can be solved by reducing them to either a maximum matching problem or an edge coloring problem for which polynomial algorithms are known. One model remains for which the complexity of the minimization problem is unknown.

The Diffie and Hellman model of a Public Key Cryptosystem has received much attention as a way to provide secure network communication. In this paper, we show that the original Diffie and Hellman model does not guarantee security against other users in the system. It is shown how users, which are more powerful adversarys than the traditionally considered passive eavesdroppers, can decrypt other users messages, in implementations of Public Key Cryptosystem using the RSA function, the Rabin function and the Goldwasser&Micali scheme. This weakness depends on the bit security of the encryption function. For the RSA (Rabin) function we show that computing, from the cyphertext, specific bits of the cleartext, is polynomially equivalent to inverting the function (factoring). As for many message spaces, this bit can be easily found out by communicating, the system is insecure. We present a modification of the Diffie and Hellman model of a Public-Key Cryptosystem, and one concrete implementation of the modified model. For this implementation, the difficulty of extracting partial information about clear text messages from their encoding, by eavesdroppers, users or by Chosen Cyphertext Attacks is proved equivalent to the computational difficulty of factoring. Such equivalence proof holds in a very strong probabilistic sense and for any message space. No additional assumptions, such as the existence of a perfect signature scheme, or a trusted authentication center, are made.