Chapter

Public Key Cryptography – PKC 2009

Volume 5443 of the series Lecture Notes in Computer Science pp 317-336

Security of Sanitizable Signatures Revisited

  • Christina BrzuskaAffiliated withDarmstadt University of Technology
  • , Marc FischlinAffiliated withDarmstadt University of Technology
  • , Tobias FreudenreichAffiliated withDarmstadt University of Technology
  • , Anja LehmannAffiliated withDarmstadt University of Technology
  • , Marcus PageAffiliated withDarmstadt University of Technology
  • , Jakob SchelbertAffiliated withDarmstadt University of Technology
  • , Dominique SchröderAffiliated withDarmstadt University of Technology
  • , Florian VolkAffiliated withDarmstadt University of Technology

Abstract

Sanitizable signature schemes, as defined by Ateniese et al. (ESORICS 2005), allow a signer to partly delegate signing rights to another party, called the sanitizer. That is, the sanitizer is able to modify a predetermined part of the original message such that the integrity and authenticity of the unchanged part is still verifiable. Ateniese et al. identify five security requirements for such schemes (unforgeability, immutability, privacy, transparency and accountability) but do not provide formal specifications for these properties. They also present a scheme that is supposed to satisfy these requirements.

Here we revisit the security requirements for sanitizable signatures and, for the first time, present a comprehensive formal treatment. Besides a full characterization of the requirements we also investigate the relationship of the properties, showing for example that unforgeability follows from accountability. We then provide a full security proof for a modification of the original scheme according to our model.