mobile police information system based on web services

TSINGHUA SCIENCE AND TECHNOLOGYI S S N 1 0 0 7 - 0 2 1 4 0 1 / 2 1 p p 1 - 7Volume 11, Number 1, February 2006

Mobile Police Information System Based on Web Services*

YIN Hao ( )**, FU Qiang ( ), LIN Chuang ( ), TAN Zhangxi ( ),

DING Rong ( ), LIN Yishu ( ), LI Yanxi ( ), FAN Yanfei ( )

Department of Computer Science and Technology, Tsinghua University, Beijing 100084, China

Abstract: The demand for communications anywhere, anytime, and on any device without recording the

date is growing with the development of modern information technologies. Current wireless communications

enable people to freely exchange information, while web services provide loosely-coupled, language-neutral,

and platform-independent ways of linking applications within organizations, across enterprises, and across

the Internet. This paper describes a mobile information system for police service, which integrates wireless

communication technologies and web service technologies. The system satisfies the special demands of

police information systems, such as security and interoperability. Policemen in the system can use various

kinds of mobile terminals, such as mobile phones, tablet PCs, personal digital assistants, and laptops

equipped with wireless LAN or GPRS to access data in the central database. The system is based on web

services with a secure web service architecture and simple object access protocol message passing.

Key words: police information system; web service; security; wireless communication

Introduction

The rapid developments in information technology

(IT), particularly in wireless communication and web

services technologies, are substantially changing the

landscape of organizational communications. Wireless

communication technologies enable people to ex-

change information anywhere, anytime, and on any

device, while web services provide technology for ser-

vice-oriented computing. Web services allow programs

written in different languages on different platforms to

communicate with each other in a standard way[1]

. By

integrating these technologies and systems, consistent

business models can be implemented on a broad array

of devices: not just on mobile devices operating over

mobile networks, but also on servers and PCs con-

nected to the Internet[1]

.

In addition, IT systems play an integral part in the

police’s capability to enforce laws and provide safety

services. A major challenge that police face is to pro-

vide a professional and consistent national policing

service, twenty-four hours a day, throughout a geo-

graphically spread population, using a broad range of

IT systems. Some parts of the police IT architecture,

such as the emergency phone system, contribute to

community safety, while other systems, such as the po-

lice radio network, provide effective coordination of

resources and a safety link for police staff working in

the field. Managing and maintaining a diverse range of

IT systems require sound solutions to ensure police

goals to be ably supported by new technologies. This

paper presents a novel integration of wireless commu-

nication technologies and web services technologies to

realize a mobile police information system to ensure

the police goals.

Received: 2004-04-01; revised: 2004-06-10

Supported by the National Natural Science Foundation of

China (Nos. 60372019 and 60473086)

To whom correspondence should be addressed.

E-mail: [email protected]

Tel: 86-10-62796495A key benefit of web services is the capability of

Tsinghua Science and Technology, February 2006, 11(1): 1-72

delivering integrated and interoperable solutions. In

police information systems, security is a key concept

that needs to be addressed as web services become

fundamental components in the system[2,3]

. The integ-

rity, confidentiality, and security of the web services

must be ensured through the application of a compre-

hensive security model which includes security topol-

ogy, platform/transport-level security, and application

layer security. This system uses a series of new secu-

rity technologies for mobile police information sys-

tems. The mobile police information system uses vari-

ous terminals (such as personal digital assistants

(PDAs)), GPRS networks, and .Net technologies.

1 Web Service Security Model

Web service security can be applied at three levels[4]

:

Platform/transport-level (point-to-point) security;

Application-level (customer) security; and

Message-level (end-to-end) security.

Each approach has different strengths and weak-

nesses described below. The choice of the approach is

largely dependent upon the characteristics of the archi-

tecture and platforms involved in the message ex-

change. The mobile information system for police ser-

vice focuses on platform- and application-level secu-

rity, so these two security levels are described with an

introduction to message-level security.

1.1 Platform/transport-level (point-to-point) security

The transport channel between two endpoints (web

service client and web service) can be used to provide

point-to-point security as illustrated in Fig. 1.

Fig. 1 Platform/transport-level security

In the platform-level model, the client sends an

XML format request to the web service. The XML

message is not encrypted by the client. When the mes-

sage is transported in the transport channel, the

network encrypts the entire data stream to make sure

that the transport is secure.

This system uses a tightly coupled Microsoft Win-

dows operating system environment. The Internet in-

formation server (IIS) provides basic, digest, integrated,

and certificate authentication. The ASP.NET web ser-

vice inherits some of the ASP.NET authentication and

authorization features. The secure sockets layer (SSL)

is used to provide message integrity and confidentiality.

1.2 Application-level security

With application-level security, the application con-

trols security with custom security features (Fig. 2).

Fig. 2 Application-level security

In the application-level security model, for example,

an application can use a custom simple object access

protocol (SOAP) header to pass user credentials to au-

thenticate the user with each web service request. A

common approach is to pass a ticket (or user name or

license) in the SOAP header. The application has the

flexibility to generate its own principal object that con-

tains roles. The application can optionally encrypt

what it needs to, although this requires secure key stor-

age and developers must have knowledge of the rele-

vant cryptography APIs. An alternative technique uses

SSL to provide confidentiality and integrity and

combine it with custom SOAP headers to perform

authentication.

The mobile police information system uses the

SOAP Toolkit 2.0[5,6]

offered by Microsoft, which pro-

vides support for internet security based on the IIS se-

curity infrastructure to implement the application-level

security model.

1.3 Message-level (end-to-end) security

Message-level security is the most flexible and power-

ful approach and is used by the global XML architec-

ture (GXA) initiative, specifically within the web

YIN Hao ( ) et al Mobile Police Information System Based on Web Services 3

service (WS)-security specification[7]

. Message-level

security is illustrated in Fig. 3.

WS-security specifications describe enhancements

to SOAP messaging that provide message integrity,

message confidentiality, and single message authenti-

cation. In this model, authentication is provided by se-

curity tokens, which flow in SOAP headers[5,8]

. No

specific type of token is required by WS-security. The

security tokens may include Kerberos tickets, X.509

certificates, or a custom binary token. Secure commu-

nication is provided by digital signatures to ensure

message integrity and XML encryption for message

confidentiality.

Fig. 3 Message-level security

2 System Architecture

2.1 Framework

Enterprise networking topologies for systems with

critical data information and security demands have

three different types: the inner model, the outer model,

and the mixed model.

In the inner model, the critical data and the applica-

tion are located in the inner part of the network, which

is protected by a firewall. The access path to the data is

through the outer part of the mobile police information

system, which focuses on authentication and authoriza-

tion issues.

The outer model topology includes two databases,

an outer database and an inner database. All the data

and applications needed by the police services are lo-

cated in the outer part of the network. When the client

calls for services, the application servers in the outer

part of the network offer the desired data from the

outer database. If the desired data are not yet in the

outer database, the outer database will get it from the

inner database. When the job is done, the application

servers will temporarily keep the information, which is

then written back into the inner database, in a special

table. The synchronization server checks the table pe-

riodically and refreshes the inner and the outer data-

bases. In the current model, all the requests are proc-

essed by only accessing the outer part of the network.

Therefore, there are less security problems with the

system, especially in the inner database where all the

critical data are stored.

The difference between those two types of network

topologies is the use of database servers in the outer

part of the network. In the inner model system, the cli-

ents access the inner part database directly so they get

the most updated data. The disadvantage of this type of

system is that the response is slow because of the long

path through the outer network. The outer topology has

better system delay performance at the expense of

maintenance costs and system complexity.

The mixture model mixes the inner and the outer

model topologies, so that one can access both the inner

part and the outer part databases. Critical data are

stored in the inner database with the data with a lower

security level stored in the outer database. The system

can provide multiple levels of data access authori-

zations so that senior police officers can directly access

the inner database whereas ordinary officers can only

access the outer database directly and the inner data-

base indirectly.

All these models can be used with the enterprise

networking architecture. The current model uses the

mixture model topology. Figure 4 illustrates the topol-

ogy structure of the mobile police information system.

The system can be implemented using various tech-

nologies such as DCOM, CORBA, and web services.

Our system is built on web services.

The client side of the system assumes that the po-

licemen will use the mobile web browser and the smart

device program on a PDA to access the information

system. Since the system is web service-based, the cli-

ent utilizes the web service to access data stored in the

database. The server side uses an application server to

authenticate the logging user and finish the authoriza-

tion. The application server offers the web service to

the client, so the PDA communicates with the applica-

tion server. The web service was named AppSevWS.

The AppSevWS also references the web service of-

fered by the database server, the data service, to get the

data from the database. The inner database service was

named IDBWS (inner database web service) while the


Fig. 4 Topology of the mixture model for mobile police information system

outer database was named ODBWS (outer database

web service).

The client sends the data request to the AppSevWS,

without caring about where the data are. The App-

SevWS does the authentication and authorization and

dispatches the corresponding web method offered by

ODBWS and IDBWS to obtain the desired data infor-

mation and pass it to the client.

Two gateways are used in the information system

for the outer and the inner parts of the system networks.

The application server is located in the outer part of the

network. The outer gateway takes charge of the secu-

rity of the application server and the outer network,

where the outer database server is located. When the

client calls for data in the inner database, the applica-

tion server calls the corresponding methods of the

IDBWS which is deployed in the inner part of the net-

work. The gateway of the inner network, which is con-

figured to only accept requests from the application

server, can confirm that the inner part of the network is

validly accessed.

2.2 Security architecture

As noted above, the security of systems with critical

information must be ensured. The analysis described in

the previous section was used to design the system se-

curity architecture in Fig. 5[9]

which shows the remote

application model for the mobile information system

for police service together with the security services

provided by the various technologies[10]

. Authentica-

tion and authorization occur at many individual points

throughout the tiers. These services are provided pri-

marily by Microsoft products, such as IIS, ASP.NET,

and SQL server. Secure communication channels are

also used throughout the tiers from the client browser

or device right through to the database. All channels

are secured using the SSL[11]

.

ASP.NET works in conjunction with IIS, the .NET

framework, and the underlying security services pro-

vided by the operating system to provide a range of au-

thentication and authorization mechanisms. These are

also summarized in Fig. 5 which illustrates the authen-

tication and authorization mechanisms provided by IIS

and ASP.NET in the system. A web request issued by

a client initiates the following sequence of authentica-

tion and authorization events[10]

:

1) The HTTPs web request is received from the net-

work. The SSL is used to ensure the server identity (using

server certificates) and the client identity. The SSL also

provides a secure channel to protect sensitive data passed

between the client and the server (and vice versa).

2) IIS authenticates the caller using basic, digest, in-

tegrated (NTLM or Kerberos), or certificate

authentication. IIS creates a Windows access token for

each authenticated user. If anonymous authentication is

selected, IIS creates an access token for the anonymous

internet user account, which, by default, is IUSR_

MACHINE.

3) IIS authorizes the caller to access the requested

resource. NTFS permissions defined by access control

lists (ACLs) attached to the requested resource are

used to authorize access. IIS can also be configured to

accept requests only from client computers with spe-

cific IP addresses.

4) IIS passes the authenticated caller’s Windows ac-

cess token to ASP.NET. This may be the anonymous

internet user’s access token, if anonymous authentica-

tion is being used.


Fig. 5 Security architecture of web application using web service

5) ASP.NET authenticates the caller: If ASP.NET is

configured for Windows authentication, no additional

authentication occurs at this point. ASP.NET will ac-

cept any token which it receives from IIS. If ASP.NET

is configured for forms authentication, the credentials

supplied by the caller (using an HTML form) are au-

thenticated against a data store; which is typically a

Microsoft SQL server database or Microsoft active di-

rectory service. If ASP.NET is configured for passport

authentication, the user is redirected to a passport site

and the passport authentication service authenticates

the user.

6) ASP.NET authorizes access to the requested re-

source or operation: The UrlAuthorization-Module (a

system provided by HTTP module) uses authorization

rules configured in Web.config (specifically, the <au-

thorization> element) to ensure that the caller can ac-

cess the requested file or folder. With Windows au-

thentication, the FileAuthorizationModule (another

HTTP module) checks that the caller has the permis-

sion to access the requested resource. The caller’s ac-

cess token is compared against the ACL which protects

the resource. .NET roles audit can also be used (either

declaratively or programmatically) to ensure that the

caller is authorized to access the requested resource or

perform the requested operation.

7) Code within the application accesses local and/or

remote resources by using a particular identity. By

default, ASP.NET performs no impersonation and, as a

result, the configured ASP.NET process account pro-

vides the identity. Alternate options include the origi-

nal caller’s identity (if impersonation is enabled), or a

configured service identity.

2.3 Security problem with mobile terminal devices

Mobile security ensures that the mobile terminal de-

vices are secure by using the following approaches:

The critical data are not stored permanently in the

device. The application will delete data

downloaded from the database before the mobile

terminal is closed.

Restrict the use of the virtual private network

(VPN) to the valid subscriber indentity module

(SIM) card which is registered in the home loca-

tion register (HLR) for special access point net-

work (APN) use.

The authentication model in the outer-part net-

work will check the device ID, user name, and

the dialing code to make sure that the device it-

self is valid.

The critical software on the device needs a user-

name and password for use.

3 Implementation

Mobile police information system consists of 5 parts.


The client side uses a smart device program called

SDAInfoSysClient. The server side has three web ser-

vices: AppSevWS, IDBWS, and ODBWS described in

Section 2. In addition, the system has a mobile web

application and a mobile web site which can be ac-

cessed by the web browser on a PDA. Figure 6 illus-

trates the components and architecture of the mobile

police information system.

Fig. 6 Mobile police information system architecture

The whole system was built using the Micro-

soft .NET framework and .NET compact framework.

On the server side, the mobile web application and the

web service are deployed on Microsoft IIS. The

IDBWS and ODBWS are associated with Microsoft

SQL Server 2000. The whole system runs on the

Windows 2003 Server platform.

Figure 7 shows the mobile web page for login in the

web browser on a pocket PC 2002. A smart device

program information page is shown in Fig. 8. Police

Fig. 7 Mobile web page (emulator view)

Fig. 8 Smart device program interface on a PDA

officers can download more critical information from

the database by the application. The system has two

gateways to protect the outer and inner parts. The

gateway interface and functions are illustrated in Fig. 9.

Fig. 9 Gateway interface

4 Conclusions

A mobile web information system was developed for

police service. The system uses software on a mobile

terminal device, such as a PDA, to interface with the

web service provided by the server to access the data

stored in the database. The whole system includes

three different web services working together to form

an information system. The security fractions are the

most important parts of the system so they were the fo-

cus of the web service when developing the system.

Future research will focus on advancing the proto-

cols of today’s XML web services standards, espe-

cially authentication, authorization, and the message-

level security of SOAP messages.

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mobile police information system based on web services

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