We propose a concept for a worldwide information security infrastructure that protects law-abiding citizens, but not criminals, even if the latter use it fraudulently (i.e. when not complying with the agreed rules). It can be seen as a middle course between the inflexible but fraudresistant KMI-proposal [8] and the flexible but non-fraud-resistant concept used in TIS-CKE [2]. Our concept consists of adding binding data to the latter concept, which will not prevent fraud by criminals but makes it P t least detectable by third parties without the need of any secret information. In [19], we depict a worldwide framework in which this concept could present a security tool that is flexible enough to be incorporated in any national cryptography policy, on both the domestic and foreign use of cryptography. Here, we present a construction for binding data for ElGamal type public key encryption schemes. As a side result we show that a particular simplification in a multiuser version of ElGamal does not s e c t its security.
Abstmct-Multilevel constructions of the binary Golay code and the Leech lattice are described. Both constructions are based upon the prvjection of the Golay code and the Leech lattice onto the (6,3,4) hexacode over GF(4). However, unlike the previously reported constructiods, the new multilevel constructions make the three levels independent by way of using a didlerent set of coset representatives for one of the quaternary coordinates. Based upon the multilevel structure of the Golay code and the Leech lattice, efficient bounded-distance decoding algorithms are devised. The bounded-distance decoder for the binary Golay code requires at most 431 operations, as compared to 651 operations Lr the best known maximum-likelihood decoder. Efficient bounded-distance decoding of the Leech lattice is achieved by means of partitioning it into four cosets of Q , , beyond the conventional partition into two cosets. The complexity of the resulting decoder is only 953 real operations on the average and 1007 operations in the worst case, as compared to about 3600 operations for the best known maximum-likelihood decoder. It is shown that the proposed algorithms decode correctly at least up to the guaranteed error-correction radius of the maximum-likelihood decoder. Thus, the loss in coding-gain is due primarily to an increase in the effective errorcoefficient, which is calculated exactly for both algorithms. Furthermore, the performance of the Leech lattice decoder on the AWGN channel is evaluated experimentally by means of a comprehensive computer simulation. The results show a loss in coding-gain of less than 0.1 dB dative to the dmum-likelihood decoder for BER ranging from lo-' to 10-'.
We suggest a decoding algorithm of-ary linear codes, which we call supercode decoding. It ensures the error probability that approaches the error probability of minimumdistance decoding as the length of the code grows. For ¡ £ ¢ ¥ ¤ the algorithm has the maximum-likelihood performance. The asymptotic complexity of supercode decoding is exponentially smaller than the complexity of all other methods known. The algorithm develops the ideas of covering-set decoding and split syndrome decoding.
Ahstrad-A new class of codes, called burst identification codes, is defined and studied. These codes can be used to determine the patterns of burst errors. Two-dimensional burst correcting codes can be easily constructed from burst identification codes. me resulting class of codes is simple to implement and has lower redundancy than other comparable codes.
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