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Reduction Optimal Trinomials for Efficient Software Implementation of the η_{T} Pairing
Toshiya NAKAJIMA Tetsuya IZU Tsuyoshi TAKAGI
Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences
Vol.E91A
No.9
pp.23792386 Publication Date: 2008/09/01 Online ISSN: 17451337
DOI: 10.1093/ietfec/e91a.9.2379 Print ISSN: 09168508 Type of Manuscript: Special Section PAPER (Special Section on Discrete Mathematics and Its Applications) Category: Keyword: pairing, software implementation, irreducible polynomial, reduction optimal trinomial, characteristic three, finite field,
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Summary:
The η_{T} pairing for supersingular elliptic curves over GF(3^{m}) has been paid attention because of its computational efficiency. Since most computation parts of the η_{T} pairing are GF(3^{m}) multiplications, it is important to improve the speed of the multiplication when implementing the η_{T} pairing. In this paper we investigate software implementation of GF(3^{m}) multiplication and propose using irreducible trinomials x^{m}+ax^{k}+b over GF(3) such that k is a multiple of w, where w is the bit length of the word of targeted CPU. We call the trinomials "reduction optimal trinomials (ROTs)." ROTs actually exist for several m's and for typical values of w = 16 and 32. We list them for extension degrees m = 97, 167, 193, 239, 317, and 487. These m's are derived from security considerations. Using ROTs, we are able to implement efficient modulo operations (reductions) for GF(3^{m}) multiplication compared with cases in which other types of irreducible trinomials are used (e.g., trinomials with a minimum k for each m). The reason for this is that for cases using ROTs, the number of shift operations on multiple precision data is reduced to less than half compared with cases using other trinomials. Our implementation results show that programs of reduction specialized for ROTs are 2030% faster on 32bit CPU and approximately 40% faster on 16bit CPU compared with programs using irreducible trinomials with general k.

