Computing pairings using <Emphasis Type="Italic">x</Emphasis>-coordinates only |
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Authors: | Steven D Galbraith Xibin Lin |
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Institution: | (1) Mathematics Department, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK;(2) School of Mathematics and Computational Science, Sun Yat-Sen University, Guangzhou, 510275, People’s Republic of China |
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Abstract: | To reduce bandwidth in elliptic curve cryptography one can transmit only x-coordinates of points (or x-coordinates together with an extra bit). This is called point compression. For further computation using the points one can
either recover the y-coordinates by taking square roots or one can use point multiplication formulae which use x-coordinates only. We consider how to efficiently use point compression in pairing-based cryptography when the embedding degree
is even. We give a method to compute compressed pairings using x-coordinates only. We also show how to compute the compressed pairings using two x-coordinates and one y-coordinate. Our methods are more efficient than taking square roots when the embedding degree is small. We implemented the
algorithms in the case of embedding degree 2 curves over where (mod 4) and found that our methods can be 10–15% faster than the analogous methods using square roots.
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Keywords: | Elliptic curves Pairings Point compression |
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