On the Security of the Digital Signature Algorithm

  • Authors:
  • Ian F. Blake;Theodoulos Garefalakis

  • Affiliations:
  • Department of Electrical and Computer Engineering, University of Toronto, Toronto, M5S 3G4, Canada ifblake@comm.toronto.edu;Department of Mathematics, Royal Hollaway College, Information Security Group, Egham, Surrey TW20 0EX, UK theo.garefalakis@rhul.ac.uk

  • Venue:
  • Designs, Codes and Cryptography
  • Year:
  • 2002

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Abstract

We present a key-recovery attack against the Digital Signature Algorithm (DSA). Our method is based on the work of Coppersmith [7], and is similar in nature to the attacks of Boneh et al. [5,9] which use lattice reduction techniques to determine upper bounds on the size of an RSA decryption exponent under which it will be revealed by the attack. This work similarly determines provable upper bounds on the sizes of the two key parameters in the DSA for which the system can be broken. Specifically if about half of the total number of bits in the secret and ephemeral keys, assuming contiguous unknown bits in each key, are known, the system can be shown to be insecure. The same technique shows that if about half of the total number of bits in two ephemeral keys are known, again assumed contiguous unknown bits in each key, but with no knowledge of the secret key, the system can be shown to be insecure.