On the effective subkey space of some image encryption algorithms using external key

Wun She Yap, Raphael C.W. Phan, Bok Min Goi, Wei Chuen Yau, Swee Huay Heng

Research output: Contribution to journalArticleResearchpeer-review

22 Citations (Scopus)


One of the general ways in designing a secure image encryption algorithm based on chaos theory is to derive a number of round subkeys from the Key Schedule algorithm under the control of an external secret key. A compulsory condition for the security of an image encryption algorithm is that the length of the external secret key should be sufficiently long in terms of bitlength. However, the sufficiently long secret key is not a guarantee that the algorithm is secure. In this paper, we emphasize the importance in designing a secure Key Schedule algorithm for such image based encryption techniques. Notably, we show why the effective space spanned by the subkeys should never be smaller than the external secret key space. To highlight the importance of this, we present our attacks on three recently proposed image encryption schemes.

Original languageEnglish
Pages (from-to)51-57
Number of pages7
JournalJournal of Visual Communication and Image Representation
Publication statusPublished - Oct 2016
Externally publishedYes


  • Attacks
  • Chaos theory
  • Image encryption
  • Key schedule
  • Key space

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