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Optimal Re-encryption Strategy for Joins in Encrypted Databases

  • Florian Kerschbaum
  • Martin Härterich
  • Patrick Grofig
  • Mathias Kohler
  • Andreas Schaad
  • Axel Schröpfer
  • Walter Tighzert
Part of the Lecture Notes in Computer Science book series (LNCS, volume 7964)

Abstract

In order to perform a join in a deterministically, adjustably encrypted database one has to re-encrypt at least one column. The problem is to select that column that will result in the minimum number of re-encryptions even under an unknown schedule of joins. Naive strategies may perform too many or even infinitely many re-encryptions. We provide two strategies that allow for a much better performance. In particular the asymptotic behavior is O(n 3/2) resp. O(n logn) re-encryptions for n columns. We show that there can be no algorithm better than O(n logn). We further extend our result to element-wise re-encryptions and show experimentally that our algorithm results in the optimal cost in 41% of the cases.

Keywords

Encrypted Database Proxy Re-encryption Adjustable Join 

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Copyright information

© IFIP International Federation for Information Processing 2013

Authors and Affiliations

  • Florian Kerschbaum
    • 1
  • Martin Härterich
    • 1
  • Patrick Grofig
    • 1
  • Mathias Kohler
    • 1
  • Andreas Schaad
    • 1
  • Axel Schröpfer
    • 1
  • Walter Tighzert
    • 1
  1. 1.SAP Applied ResearchKarlsruheGermany

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