Some active attacks on fast server-aided secret computation protocols for modular exponentiation

  • Hwang Shin-Jia 
  • Chang Chin-Chen 
  • Yang Wei-Pang 
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 1029)


Four server-aided secret computation protocols, Protocols 1, 2, 3, and 4, for modular exponentiation were proposed by Kawamura and Shimbo in 1993. By these protocols, the client can easily compute the modular exponentiation Md mod N with the help of a powerful server, where N is the product of two large primes. To enhance the security, the client was suggested to use a verification scheme and a slight modification on each proposed protocol. In this paper, we propose two new active attacks to break Protocols 3 and 4, respectively. Even if Protocols 3 and 4 have included the slight modification and verification, the untrusted server can still obtain the secret data d. The client cannot detect these attacks by the proposed verification. To adopt these new attacks, the difficulty of finding the value of the secret data d will be decreased drastically.


server-aided secret computation protocol active attack cryptography modular exponentiation 


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Copyright information

© Springer-Verlag Berlin Heidelberg 1996

Authors and Affiliations

  • Hwang Shin-Jia 
    • 1
  • Chang Chin-Chen 
    • 2
  • Yang Wei-Pang 
    • 1
  1. 1.Institute of Computer and Information ScienceNational Chiao Tung UniversityHsinchuTaiwan 300, ROC
  2. 2.Institute of Computer Science and Information EngineeringNational Chung Cheng UniversityChiayiTaiwan 621, ROC

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