Attacking right-to-left modular exponentiation with timely random faults

  • Authors:
  • Michele Boreale

  • Affiliations:
  • Dipartimento di Sistemi e Informatica, Università di Firenze

  • Venue:
  • FDTC'06 Proceedings of the Third international conference on Fault Diagnosis and Tolerance in Cryptography
  • Year:
  • 2006

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Abstract

We show that timely induction of random failures can potentially be used to mount very cost effective attacks against smartcards deploying cryptographic schemes based on (right-to-left) modular exponentiation. We introduce a model where an external perturbation, or glitch, may cause a single modular multiplication to produce a truly random result. Based on this assumption, we present a probabilistic attack against the implemented cryptosystem. Under reasonable assumptions, we prove that using a single faulty signature the attack recovers a target bit of the secret exponent with an error probability bounded by $\frac 3 7$. We show the attack is effective even in the presence of message blinding.