  This paper re-evaluates the security of a chaotic image encryption algorithm
called MCKBA/HCKBA and finds that it can be broken efficiently with two known
plain-images and the corresponding cipher-images. In addition, it is reported
that a previously proposed breaking on MCKBA/HCKBA can be further improved by
reducing the number of chosen plain-images from four to two. The two attacks
are both based on the properties of solving a composite function involving the
carry bit, which is composed of the modulo addition and the bitwise OR
operations. Both rigorous theoretical analysis and detailed experimental
results are provided.

Cryptography and Security