978-1-5090-3710-0/16/$31.00 ©2016 IEEE 791
2016 9th International Congress on Image and Signal Processing, BioMedical Engineering and Informatics(CISP-BMEI 2016)
Optical Encryption of Gray Image Based on the
Fourier Computer Generated Hologram and Logical
Modulation
Ying Wang
School of Electronics and Information Engineering
Sichuan University
Chengdu, China
Irene_1993@163.com
Qiong-Hua Wang
School of Electronics and Information Engineering
Sichuan University
Chengdu, China
qhwang@scu.edu.cn
Qi Liu
School of Electronics and Information Engineering
Sichuan University
Chengdu, China
lqdreaming@163.com
Jun Wang*
School of Electronics and Information Engineering,
Sichuan University
Chengdu, China
jwang@scu.edu.cn
Abstract—In this paper, we proposed a novel optical encryption
and decryption method of gray image based on the Fourier
computer-generated hologram (CGH) and logical modulation.
Since the encryption method using the CGH or the logical
modulation alone has a shortness of low security, the proposed
novel encryption combines the two methods together. In our
encryption processing, the hologram, which is gotten by Fourier
transform from the original image, is encrypted by logical
modulation with the chaotic sequence. Simulation results and
analysis show that the security and robustness of the proposed
approach has a satisfactory performance.
Keywords—Fourier transform; computer-generated hologra
m; chaotic logical modulation.
I. I
NTRODUCTION
With the development
of information networks, more and
more
private and secret image information needs to be
protected. In the past decades, encryption algorithm has been
developed quickly and various optical encryption algorithms
have been put forward and investigated [1-2]. Optical image
encryption has many advantages, such as high speed and
parallelism in processing. Any wavelength and system
parameters can be used in the CGH. In addition, CGH is
easier to implement. Therefore, image encryption based on
CGH becomes a hot issue in the research of image encryption
[3]. Many researchers have focused on optical encryption
based on CGH. An optical image encryption of 4f system
double random-phase proposed by Refregier and Javidi [4],
the most classical and important method, is used widely,
others are its deprived and improved cryptosystems such as
based on fractional cryptosystems, such as in fractional
Fourier transform domain [5-6], Fresnel transform
domain[7-8] and Joint transform co-relator [9] of optical
encryption system was proposed, solving the previous
problem that encryption secret is the complex conjugate of
decryption secret. However, the method of the above mention
is also complicated.
The chaotic system [10-11] has many interesting
characteristics: sensitivity with initial values and good
characteristic of random distribution, which completely
satisfy the basic requirements of cryptography. In recent years,
many researchers have carried on a lot of researches and the
analysis for the chaotic cryptography system. And these
researches prove that the encryption method based on chaotic
system has some good properties in many aspects such as
security, complexity, computation speed. In optical hologram
encryption, the diffraction distance, the secret key of the
system, now initial value could be used as additional keys to
enlarge key spaces of the system significantly. Serving the
right secret keys of the system, original image will be
reconstruction. Since previous methods based on CGH, totally
dependent on software, most of them lack of flexibility.
In this paper, we proposed a new image encryption
approach based on the CGH and the chaotic logical
modulation to overcome their shortcomings and to enhance
the security of system at the same time. The new encryption
scheme can also be implemented by the optical system setup
with many inherent and attractive advantages, such as
parallelism and high speed in processing. We also analysis the
feasibilities of robustness against occlusions and noise attack
by a set of numerical simulations.
II. T
HE
P
ROPOSED
M
ETHOD
Our proposed method includes two mainly parts: Fourier
CGH and logical modulation.
The encryption and decryption
processes is shown in Fig. 1.
In the encryption processing, the
encrypted hologram is obtained through logical modulating
with chaotic sequence. The logical modulation in our method
is a kind of encryption technology based on binary logical
operation. Assuming that the information to be encrypted is
Fourier CGH, and the information of secret key is chaotic
sequence, then every pixel value of Fourier CGH and chaotic
sequence is transformed into binary value and the two binary
values operates with bit-wise XOR to obtain the encryption
image. The reverse process of the encryption process is the
decryption process