A New Class of Weak Encryption Exponents in RSA

  • Authors:
  • Subhamoy Maitra;Santanu Sarkar

  • Affiliations:
  • Indian Statistical Institute, Kolkata, India 700 108;Indian Statistical Institute, Kolkata, India 700 108

  • Venue:
  • INDOCRYPT '08 Proceedings of the 9th International Conference on Cryptology in India: Progress in Cryptology
  • Year:
  • 2008

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Abstract

Consider RSA with N = pq , q p q , public encryption exponent e and private decryption exponent d . We concentrate on thecases when e ( = N α )satisfies eX - ZY = 1, given |N -Z | = N τ . Using the ideaof Boneh and Durfee (Eurocrypt 1999, IEEE-IT 2000) we show that theLLL algorithm can be efficiently applied to get Z when|Y | = N v and γ Z = ψ (p , q , u ,v ) = (p - u )(q - v ).Further, we consider Z = ψ (p ,q , u , v ) = N - pu -v to provide a new class of weak keys in RSA. This ideadoes not require any kind of factorization as used in Nitaj's work.A very conservative estimate for the number of such weak exponentsis N 0.75 - ε , whereε 0 is arbitrarily small for suitably largeN .