  This paper analyzes security performance of an image encryption algorithm
using 2D lag-complex Logistic map (LCLM), which adopts it as a pseudo-random
number generator, and uses the sum of all pixel values of the plain-image as
its initial value to control the random combination of the basic encryption
operations. However, multiple factors make the final pseudo-random sequences
controlling the encryption process may be the same for different plain-images.
Based on this point, we proposed a chosen-plaintext attack by attacking the six
encryption steps with a strategy of divide and conquer. Using the pitfalls of
2D-LCLM, the number of required chosen plain-images is further reduced to
$5\cdot\log_2(MN)+95$, where $\mathit{MN}$ is the number of pixels of the
plain-image.
