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.
|Number of pages||7|
|Journal||Journal of Visual Communication and Image Representation|
|Publication status||Published - Oct 2016|
- Chaos theory
- Image encryption
- Key schedule
- Key space