Characterization of the relations between information-theoretic non-malleability, secrecy, and authenticity

  • Authors:
  • Akinori Kawachi;Christopher Portmann;Keisuke Tanaka

  • Affiliations:
  • Department of Mathematical and Computing Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan;Department of Mathematical and Computing Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan;Department of Mathematical and Computing Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan

  • Venue:
  • ICITS'11 Proceedings of the 5th international conference on Information theoretic security
  • Year:
  • 2011

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Abstract

Roughly speaking, an encryption scheme is said to be nonmalleable, if no adversary can modify a ciphertext so that the resulting message is meaningfully related to the original message. We compare this notion of security to secrecy and authenticity, and provide a complete characterization of their relative strengths. In particular, we show that information-theoretic perfect non-malleability is equivalent to perfect secrecy of two different messages. This implies that for n-bit messages a shared secret key of length roughly 2n is necessary to achieve non-malleability, which meets the previously known upper bound. We define approximate non-malleability by relaxing the security conditions and only requiring non-malleability to hold with high probability (over the choice of secret key), and show that any authentication scheme implies approximate non-malleability. Since authentication is possible with a shared secret key of length roughly log n, the same applies to approximate non-malleability.