The Bit Security of Modular Squaring Given Partial Factorization of the Modulos

  • Authors:
  • Benny Chor;Oded Goldreich;Shafi Goldwasser

  • Affiliations:
  • -;-;-

  • Venue:
  • CRYPTO '85 Advances in Cryptology
  • Year:
  • 1985

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Abstract

It is known that given a composite integer N = p1p2 - such that p1 驴 p2 驴 3 (mod 4)), and q a quadratic residue modulo N, guessing the least significant bit of a square root of q with any non-negligible advantage is as hard as factoring N.In this paper we extend the above result to multi-prime numbers N = p1p2...p1 (such that p1 驴 p2 驴 ... 驴 p1 驴 3 (mod 1)). We show that given N and q, a quadratic residue mod N, guessing the least significant bit of a square root of q is as hard as completely factoring N. Furthermore, the difficulty of guessing the least significant bit of the square root or q remains unchanged evert when all but two of the prime factors of N, p3,...,p1, are known. The result is useful in desigihg multi-party cryptographic protocols.