  To encrypt sensitive information existing in a color DICOM images, a medical
privacy protection scheme (called as MPPS) based on chaos and DNA coding was
proposed by using two coupled chaotic systems to produce cryptographic
primitives. Relying on some empirical analyses and experimental results, the
designers of MPPS claimed that it can withstand a chosen-plaintext attack and
some other classic attacking models. However, this statement is groundless. In
this paper, we investigate the essential properties of MPPS and DNA coding, and
we then propose an efficient chosen-plaintext attack to disclose its equivalent
secret-key. The attack only needs $\lceil \log_{256}(3\cdot M\cdot N)\rceil+4$
pair of chosen plain-images and the corresponding cipher-images, where $M
\times N$ and ``3" are the size of the RGB color image and the number of color
channels, respectively. In addition, the other claimed superiorities are
questioned from the perspective of modern cryptography. Both theoretical and
experimental results are presented to support the efficiency of the proposed
attack and the other reported security faults. The proposed cryptanalysis
results will promote the proper application of DNA encoding to protect
multimedia privacy data, especially that in a DICOM image.
