perceptual encryption method for vector map based on
TRANSCRIPT
Perceptual Encryption Method for Vector Map Based
on Geometric Transformations
Giao P.N 1, Oh-Jun Kwon 2, Suk-Hwan Lee 3 and Ki-Ryong Kwon 4 1, 4 Dept. of IT Convergence & Application Engineering, Pukyong National University, Pusan, South Korea
2 Dept. of Computer Software Engineering, Dong-Eui University, Pusan, South Korea 3 Dept. of Information Security, Tongmyong University, Pusan, South Korea
E-mail: [email protected], [email protected], [email protected], [email protected]
Abstract β Currently, there are many applications used vector
map data widely. But the production of vector map consumes a
lot of money and human resource while vector map data is bought
by any user or attacked by pirates, and then they distributed
vector map data easily without permission from providers. So,
provider desires a method to encrypt vector map data before
storing and transmitting to ensure the access control and prevent
illegal copying of it. This paper presents a perceptual encryption
method for vector map data based on encrypting geometric
objects in the frequency domain of discrete cosine transform.
Geometric objects in vector map are changed by geometric
transformations. After that, they are encrypted selectivity in the
frequency domain of discrete cosine transform to obtain
encrypted objects. In experiments, vector map data is changed
entirely after encryption process, and the proposed method is very
effective for a large of vector map datasets.
I. INTRODUCTION
Vector map data is a vectorβbased collection of Geographic
Information System (GIS) data about earth at various levels of
detail. Vector map is created and developed by the merging
system of cartography, statistical analysis, and database
technology based on vector model [1-2]. Because it has more
advantages than raster map, vector map is used in many
applications in life. But the production of a vector map is
considerably complex, and the maintenance of a digital map
requires substantial monetary, human resources. And any
company can buy it, make illegal copies and distribute or sell
them easily many times without taking any permission from the
original GIS data provider. So, producer or provider desires a
method to encrypt vector map data before storing and
transmitting to ensure the access control and prevent illegal
copying of it.
For meeting above requirement, in this paper we present a
perceptual encryption method for vector map data for the
secured storage and transmission. In the proposed method, we
selected and changed the geometric objects of vector map data
by geometric transformation, and then we encrypt them
selectivity in the frequency domain of discrete cosine transform
(DCT). The main advantages of our algorithm is simple
computing but it still meets requirements of security, and it can
be applied to the various formats of vector map data. In order
to understand the detailed content of algorithm, our paper is
organized as follows. In section 2, we look into the vector map
security techniques and discuss the relation of vector map data
to the proposed scheme. In section 3, we explain the proposed
algorithm in detail. And section 4, we perform experiments and
discuss about the experimental results, evaluate the
performance of algorithm. Conclusion is shown in section 5 in
this paper.
II. RELATED WORKS
A. Vector Map Encryption
Bertino et al. [3], Chena et al. [4], and Rybalov et al. [5]
presented approaches to the definition of an access control
system for spatial data on the Web. Mostly, authors explained
technical challenges raised by the unique requirements of
secure geospatial data management such as access control,
security and privacy policies. But access control and
management on Web or database do not maintain security in
the outflow of an authenticated user. Wu et al. [6] proposed a
compound chaos-based encryption algorithm of vector data by
considering the storage characteristics and sensitivity of the
initial values and parameters of chaos-based systems. This
algorithm is not available to various data formats and object
indexing. Li et al. [7] encrypted the vector dataset in external
Oracle DBMS by using DES and an R-Tree spatial index. This
algorithm does not keep the security of the vector map on the
DBMS because key length is short. Dakroury et al. [8] also
described better encrypting algorithm which combined AES
and RSA cryptography with a simple watermarking technique
for the copyright protection of vector map data in on/off line
service. This algorithm encrypts all parts of vector map data
using an AES block cipher operator of 256 bits. That mean it
encrypted unnecessary data of vector map data.
B. Vector Map Data Based Perceptual Encryption
Vector map data is stored in layers. Each layer includes an
amount of vector data which is described by geometric objects
as point, polyline and polygon. Point is used to represent simple
objects as position while polygon and polyline are used to
represent complex objects as road, contour line and boundaries
[9]. Real objects are described on the map based on
geographical features and by geometric objects. So, vector map
encryption should be based on them. Thus, polyline and
polygon are considered be very important components of
vector map. In our method, polyline and polygon data in layer
is selected and extracted for perceptual encryption.
Fig. 1 The proposed algorithm.
III. THE PROPOSED METHOD
A. Overview
The proposed method is shown detail in Fig. 1. Geometric
objects (polyline and polygon) are extracted from vector map
data, and they are used together with key value to generate
shearing vector. Next, geometric objects are distorted by
distorting process using shearing vector. After that, distorted
object will be transform to DCT domain by forward DCT
process. In DCT domain, we perform selective encryption for
DCT coefficients. DC value is selected for encryption process
in DCT domain. Due to DC value was changed by encryption
process, after inverse DCT process, we get new geometric
object. Finally, we continue to use shearing vector for
distorting process new object above to obtain encryption object.
B. Perceptual encryption process
A vector map contains number of layers. We consider a layer
π³ contains a number of objects of polylines/polygons π³ ={ππ|π β [1, |π³|]}, and an object contains a series of vertices ππ ={π£π,π|π β [1, |ππ|]}. |L| and |ππ| are cardinalities of a layer L, and
an object ππ . Thus, π£π,π indicates ππ‘β vertex in ππ‘β object of
layer L and is defined as two coordinates π£π,π = (π₯π,π , π¦π,π). To
brief, we define main notation following theory above:
An object ππ = {π£π,π|π β [1, |ππ|]}
Shearing vector for ππ is ππ = {π π,π|π β [1, |ππ|]}
π is key value for encryption object, is created by hashing
function
πβ²π = {π£β²π,π|π β [1, |ππ|]} is distorted object
π π = {ππ,π|π β [1, |ππ|]} is a set of DCT coefficients of
distorted object after DCT process
π β²π = {πβ²π,π
|π β [1, |ππ|]} is a set of DCT coefficients of
object after inverse DCT
ππ = {ππ,π|π β [1, |ππ|]} is encrypted object
π·πΆπ, πΌπ·πΆπ are forward and inverse DCT process
π·(. ) is distorting process
Shearing vector ππ is a set of values that they are generated
by key value K and parameter the number of vertices in object
ππ by (1). Key value K is created by SHA-512 hashing
algorithm from user key with key length is 512 bit for each key
[10].
π π,π = π. π +(π + 1). (π + 2)
|ππ| (1)
Object π π is distorted by shearing vector ππ shown in (2):
πβ²π = π·(ππ , π π)
= {(π π,π + π. π). π£π,π|π β [1, |ππ|]}
= {π£β²π,π|π β [1, |ππ|]} (2)
with π£β²π,π = (π π,π + π. π). π£ π,π. Distorted object πβ²π is transform
to DCT domain by forward DCT process as (3):
π π = π·πΆπ(πβ²π)
= {ππ,π|π β [1, |ππ|]} (3)
DC value of π π is ππ,1 be encrypted by key value K in (4):
ππ π,1
= π +ππ,1
π (4)
After that, DCT coefficients are changed by inverse DCT
process as (5). Due to ππ,1 changing to πππ,1, thus π β²π is always
different π π .
π β²π = πΌπ·πΆπ(π π) = {πβ²π,π|π β [1, |ππ|]} (5)
Finally, encrypted object ππ is obtained from π β²π by distorting
process using shearing vector ππ by (6):
ππ = π·(ππ , π β² π)
= {(π π,π + π. π). πβ²π,π|π β [1, |ππ|]}
= {ππ,π|π β [1, |ππ|]} (6)
C. Decryption process
Following steps in perceptual encryption in Fig. 1, we also
extract polylines/polygons from encrypted map, and then using
Vector mapSi
Key Value K
EiEncrypted
Vector mapPi Shearing Vector
Distort Object DCTDC
EncryptionIDCT
Distort Object
Pβi FiFβi
HashingUser Key
key value and number of vertices in an object for generating
the shearing vector. After that, we perform inverse processes
with processes in encryption to receive decrypted map.
IV. EXPERIMENTAL RESULTS
A. Visualization
We used vector maps of Wales with road, natural and
railway layers in visualization experiences. Vector map data
format is shape-file (SHP) format. It is popular geographical
vector data format. The proposed algorithm is applied to
polylines/polygons in shape-files. Experimental results are
shown in Fig. 2 and Fig. 4. Maps are changed entirely after
perceptual encryption process. The proposed method is
originality and unique than previous algorithms, because we
only encrypted vertices of object. The proposed algorithm is
also lower computational complexity than AES or DES
because we only encrypt DC value in DCT domain.
(a)
(b)
Fig. 2 (a) Original Wales road map, and (b) Encrypted Wales road map
(a)
(b)
Fig. 3 (a) Original Wales railways, and (b) Encrypted Wales railways
(a)
(b)
Fig. 4 (a) Original Wales natural, and (b) Encrypted Wales natural
B. Security evaluation
Number of objects
0 100 200 300 400 500 600 700
Ent
ropy
0
1000
2000
3000
4000
5000
6000
Entropy according to number of objects
Fig. 5 Entropy of proposed method according to number of objects
In order to extract information from the perceptual encrypted
map, any pirate has to extract all encrypted objects of map
without knowledge of keys. So, if the randomness of perceptual
encryption is high, it will be so difficult to attack encrypted
objects. Therefore, we will analyzed the entropy of perceptual
encrypted map to evaluate the security of proposed method.
From equations in Section 3, we can see that the randomness
of encrypted map be depended on key value K and the number
of objects in map. Fig. 5 shows the entropy of proposed method
according to number of object in map. If number of object in
map is high, the entropy will be high.
C. Computation time
Looking in Fig. 6, we see that the computation time of
proposed method is lower than the computation time of Wuβs
method [6] and Dakrouryβs method [8]. Because the
computation time of proposed method is dependent on the
number of objects and DCT process. So, the proposed method
is faster than previous methods. Fig. 6 shows the computation
time of proposed method according to the size of map, and
compares it with previous methods.
Fig. 6: Computation time
V. CONCLUSIONS
In this paper, we proposed the perceptual encryption algorithm
for vector map data security based on geometric transformation
and DCT domain. Experimental results showed that the
proposed algorithm is very effective with a large volume of
vector map dataset. It also responses to various formats of
vector map data. Comparing to previous algorithms, the
proposed method has higher security because the security of
proposed method is dependent on the number of objects in map.
The computation time of proposed method is also shorter than
previous method. Furthermore, my algorithm can be applied to
various vector contents such as CAD and 3D content fields.
ACKNOWLEDGMENT
"This research was supported by the MSIP(Ministry of
Science, ICT and Future Planning), Korea, under the Grand
Information Technology Research Center support program
(IITP-2016-R71181610050001002) supervised by the
IITP(Institute for Information & communications Technology
Promotion)β and Basic Science Research Program through the
National Research Foundation of Korea (NRF) funded by the
Ministry of Education, Science and Technology (NRF-2011-
0023118) and (NRF-2014-0006663).β
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