A.Kh. Al Jabri

Zero-Error Codes for Correlated Information Sources

Slepian and Wolf [2] gave a characterization for the compression region of distributed correlated sources. Their result is for codes with a decoding probability of error approaching zero as the code length is increased. Of interest in many applications is to find codes for which the probability of error is exactly zero. For this latter case, block codes using the zero-error information between the sources have been proposed by Witsenhausen [3]. Better codes, however, can be obtained by further exploitation of the statistical dependency impeded in the correlation information. In this paper variable-length zero-error codes are proposed that are generally more efficient than Witsenhausen codes. A method for their construction is presented and an example demonstrating such construction with the achieved rate region are given.

A Statistical Decoding Algorithm for General Linear Block Codes

This paper introduces a new decoding algorithm for general linear block codes. The algorithm generates a direct estimate of the error locations based on exploiting the statistical information embedded in the classical syndrome decoding. The algorithm can be used to cryptanalyze many algebraic-code public-key crypto and identification systems. In particular results show that the McEliece public-key cryptosystem with its original parameters is not secure.

Secure progressive transmission of compressed images

In most progressive image coding techniques the compressed data vary in importance for reconstructing the original image. Obtaining certain parts of these data by an eavesdropper could reveal significant information about the transmitted or stored image. In this paper different encryption methods to secure the transmission or storage of such data are proposed and evaluated. The methods are chosen in a manner that allows high encryption and decryption rates, simple key management and utilization of widely available encryption algorithms such as the DES (data encryption standard). Effects of channel noise on the encrypted data are also considered and a modification of these methods to combat channel errors is also proposed and evaluated.

Shrinking generators and statistical leakage

Shrinking is a newly proposed technique for combining a pair of pseudo random binary sequences, (a,s), to form a new sequence, z, with better randomness, where randomness here stands for difficulty of prediction. The ones in the second sequence s are used to point out the bits in the sequence a to be included in z. The generator that performs this process is known as the shrinking generator (SG). In this paper, it is shown for the existing combining method that deviation from randomness in the statistics of a leads to the leakage of this statistics into z. We also show that it is sufficient for constructing a statistically balanced SG to at least have one statistically balanced generator. A new shrinking rule that yields statistically balanced output, even if a and s are not balanced, is then proposed. Self-shrinking in which a single pseudo random bit generator (PRBG) shrinks itself is also investigated and a modification of the existing shrinking rule is proposed. Simulation results show the robustness of the proposed methods. For self-shrinking, in particular, results show that the proposed shrinking rule yields sequences with balanced statistics even for extremely biased generators. This suggests possible application of the new rule to strengthen running key generators.

The unicity distance: an upper bound on the probability of an eavesdropper successfully estimating the secret key

The unicity distance, U, of a secret-key cipher is defined by Shannon as the minimum amount of intercepted ciphertext symbols needed, in principle, to uniquely determine the secret key and, therefore, break the cipher. Accordingly, for a ciphertext of size N symbols less than U, the estimated key will have a nonzero probability of error. Of interest is knowing the chance or probability that an eavesdropper, using the best estimation rule, successfully estimates the secret key from N ciphertext symbols less than U. An upper bound on this probability is derived in this paper.

Adaptive power transmission schemes for meteor-burst communication

Different transmission schemes are known in the literature to optimize the performance of systems operating on the meteor-burst channel. In general these schemes can be classified into variable or fixed rate schemes. In this paper we propose and analyze a new adaptive-power, fixed-rate, transmission scheme for meteor-burst channel. In this scheme, symbols with low power are transmitted at the beginning of the burst while symbols with high power are transmitted at the end of the burst. A method to implement the proposed scheme is described and its performance is compared to the performance of systems with fixed power transmission. It is found that a saving of approximately 37% in the transmitted energy can be achieved using the adaptive power scheme compared to systems with fixed-power transmission. >Different transmission schemes are known in the literature to optimize the performance of systems operating on the meteor-burst channel. In general these schemes can be classified into variable or fixed rate schemes. In this paper we propose and analyze a new adaptive-power, fixed-rate, transmission scheme for meteor-burst channel. In this scheme, symbols with low power are transmitted at the beginning of the burst while symbols with high power are transmitted at the end of the burst. A method to implement the proposed scheme is described and its performance is compared to the performance of systems with fixed power transmission. It is found that a saving of approximately 37% in the transmitted energy can be achieved using the adaptive power scheme compared to systems with fixed-power transmission.<<ETX>>

A symmetric version of the McEliece public-key cryptosystem

This article exploits the fact that linear codes can correct twice the number of erasures as that of errors, allowing reduction in code size and providing the same level of security.

Private-key algebraic-code encryption with errors up to (d min − 1) of the code

In most algebraic-code cryptosystems errors are added to the encoded plaintext to form the ciphertext. The number of added errors is usually less than or equal to the error-correcting capability of the code. In this paper we propose a method that permits the addition of almost double the number of these errors. The idea is based on the fact that linear codes can correct twice as many erasures as errors. A method for erasure creation, detection and correction is devised. Such an approach will allow for the addition of a number of errors that can not be corrected without side information about their position. This approach will result in a further increase in the security of these systems compared to systems with errors only. Based on this idea, a private-key cryptosystem with simple codes and permutations only is proposed and its security is evaluated.

Channels with insertion and/or deletion and their capacity

Knowledge of limits on possible reliable transmission rates on communication channels is of practical interest. In the paper, the capacity of a class of communication channels with insertion or deletion is investigated.<<ETX>>

Unstructured to structured error correction using neural nets

Most transmitted or stored information are subjected to occasional errors. In most situations, the source of this information has inherent unstructured redundancy that can be exploited to correct these errors. In addition to the storage requirements, getting the source statistics required to perform the error correction may not be easy. In this paper, we propose and evaluate trained neural nets to transform the unstructured redundancy into a structured one. The new approach, eliminates the need for source statistics storage and also simplifies the decoding process. This idea is applied to correct some of the errors caused by passing a printed Arabic text through an optical character recognition (OCR) device. Simulation results demonstrate the effectiveness of this technique.<<ETX>>