New Algorithm for Classical Modular Inverse

  • Authors:
  • Róbert Lórencz

  • Affiliations:
  • -

  • Venue:
  • CHES '02 Revised Papers from the 4th International Workshop on Cryptographic Hardware and Embedded Systems
  • Year:
  • 2002

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Abstract

The Montgomery inverse is used in cryptography for the computation of modular inverse of b modulo a, where a is a prime. We analyse existing algorithms from the point of view of their hardware implementation. We propose a new, hardware-optimal algorithm for the calculation of the classical modular inverse. The left-shift binary algorithm is shown to naturally calculate the classical modular inverse in fewer operations than the algorithm derived from the Montgomery inverse.