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On Diffie-Hellman Key Agreement with Short Exponents

  • Paul C. van Oorschot
  • Michael J. Wiener
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 1070)

Abstract

The difficulty of computing discrete logarithms known to be “short” is examined, motivated by recent practical interest in using Diffie-Hellman key agreement with short exponents (e.g. over Z p with 160-bit exponents and 1024-bit primes p). A new divide-and-conquer algorithm for discrete logarithms is presented, combining Pollard’s lambda method with a partial Pohlig-Hellman decomposition. For random Diffie-Hellman primes p, examination reveals this partial decomposition itself allows recovery of short exponents in many cases, while the new technique dramatically extends the range. Use of subgroups of large prime order precludes the attack at essentially no cost, and is the recommended solution. Using safe primes also precludes this particular attack and allows improved exponentiation performance, although parameter generation costs are dramatically higher.

Keywords

Prime Divisor Discrete Logarithm Discrete Logarithm Problem Modular Exponentiation Lambda Method 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 1996

Authors and Affiliations

  • Paul C. van Oorschot
    • 1
  • Michael J. Wiener
    • 1
  1. 1.Bell-Northern ResearchOttawaCanada

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