applied cryptography - protocols, algorithms, and source code in c

One way to lower the constant is to find better ways

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Unformatted text preview: omputation over GF(2n) is often quicker than computation over GF(p). Just as exponentiation is much more efficient in GF(2n), so is calculating discrete logarithms [180, 181, 368, 379]. If you want to learn more about this, read [140]. For a Galois field GF(2n), cryptographers like to use the trinomial p (x) = xn + x + 1 as the modulus, because the long string of zeros between the xn and x coefficients makes it easy to implement a fast modular multiplication [183]. The trinomial must be primitive, otherwise the math does not work. Values of n less than 1000 [1649, 1648] for which xn + x + 1 is primitive are: 1, 3, 4, 6, 9, 15, 22, 28, 30, 46, 60, 63, 127, 153, 172, 303, 471, 532, 865, 900 There exists a hardware implementation of GF(2127) where p (x) = x127 + x + 1 [1631, 1632, 1129]. Efficient hardware architectures for implementing exponentiation in GF(2n) are discussed in [147]. 11.4 Factoring Factoring a number means finding its prime factors. 10 = 2*5 60 = 2*2*3*5 252601 = 41*61*101 2113 - 1 = 3391*23279*65993*1868569*1066818132868207 The factoring problem is one of the oldest in number theory. It’s simple to factor a number, but it’s time-consuming. This is still true, but there have been some major advances in the state of the art. Currently, the best factoring algorithm is: Number field sieve (NFS) [953] (see also [952,16,279]). The general number field sieve is the fastest-known factoring algorithm for numbers larger than 110 digits or so [472,635]. It was impractical when originally proposed, but that has changed due to a series of improvements over the last few years [953]. The NFS is still too new to have broken any factoring records, but this will change soon. An early version was used to factor the ninth Fermat number: 2512 + 1 [955,954]. Other factoring algorithms have been supplanted by the NFS: Quadratic sieve (QS) [1257,1617,1259]. This is the fastest-known algorithm for numbers less than 110 decimal digits long and has been used extensively [440]. A faster version of this algorithm is called the multiple polynomial quadratic sieve [1453,302]. The fastest version...
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This note was uploaded on 10/18/2010 for the course MATH CS 301 taught by Professor Aliulger during the Fall '10 term at Koç University.

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