Weak Keys for IDEA

  • Joan Daemen
  • René Govaerts
  • Joos Vandewalle
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 773)


Large classes of weak keys have been found for the block cipher algorithm IDEA, previously known as IPES [2]. IDEA has a 128-bit key and encrypts blocks of 64 bits. For a class of 223 keys IDEA exhibits a linear factor. For a certain class of 235 keys the cipher has a global characteristic with probability 1. For another class of 251 keys only two encryptions and solving a set of 16 nonlinear boolean equations with 12 variables is sufficient to test if the used key belongs to this class. If it does, its particular value can be calculated efficiently. It is shown that the problem of weak keys can be eliminated by slightly modifying the key schedule of IDEA.


Block Cipher Linear Factor Round Function Differential Cryptanalysis Search Encryption 
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.


  1. [1]
    X. Lai and J.L. Massey, A Proposal for a New Block Encryption Standard, Advances in Cryptology-Eurocrypt’ 90, Springer-Verlag, Berlin 1991, pp. 389–404.Google Scholar
  2. [2]
    X. Lai, J.L. Massey and S. Murphy, Markov Ciphers and Differential Cryptanalysis, Advances in Cryptology-Eurocrypt’ 91, Springer-Verlag, Berlin 1991, pp. 17–38.Google Scholar
  3. [3]
    E. Biham and A. Shamir, Differential Cryptanalysis of DES-like Cryptosystems, Journal of Cryptology, Springer-Verlag, Vol. 4, No. 1, pp. 3–72, 1991.CrossRefzbMATHMathSciNetGoogle Scholar
  4. [4]
    D. Chaum, J.-H. Evertse, Cryptanalysis of DES with a Reduced Number of Rounds, Sequences of Linear Factors in Block Ciphers, Advances in Cryptology, Proceedings of Crypto 85, pp. 192–211, 1985.Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 1994

Authors and Affiliations

  • Joan Daemen
    • 1
  • René Govaerts
    • 1
  • Joos Vandewalle
    • 1
  1. 1.Laboratorium ESATKatholieke Universiteit LeuvenHeverleeBelgium

Personalised recommendations