On the Unpredictability of Bits of the Elliptic Curve Diffie--Hellman Scheme

  • Authors:
  • Dan Boneh;Igor Shparlinski

  • Affiliations:
  • -;-

  • Venue:
  • CRYPTO '01 Proceedings of the 21st Annual International Cryptology Conference on Advances in Cryptology
  • Year:
  • 2001

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Abstract

Let E/Fp be an elliptic curve, and G ∈ E/Fp. Define the Diffie-Hellman function as DHE,G(aG, bG) = abG. We show that if there is an efficient algorithm for predicting the LSB of the x or y coordinate of abG given 〈E, G, aG, bG〉 for a certain family of elliptic curves, then there is an algorithm for computing the Diffie-Hellman function on all curves in this family. This seems stronger than the best analogous results for the Diffie-Hellman function in F*p. Boneh and Venkatesan showed that in F*p computing approximately (log p)1/2 of the bits of the Diffie-Hellman secret is as hard as computing the entire secret. Our results show that just predicting one bit of the Elliptic Curve Diffie-Hellman secret in a family of curves is as hard as computing the entire secret.