A PERFORMANCE EVALUATION OF MOBILE WEB SERVICES

SECURITY

Satish Narayana Srirama

, Matthias Jarke

1,2

and Wolfgang Prinz

1,2

RWTH Aachen, Informatik V, Ahornstr.55, 52056 Aachen, Germany

Fraunhofer FIT, Schloss Birlinghoven, 53754 Sankt Augustin, Germany

Keywords: Mobile web services, mobile web service provisioning, WS-Security.

Abstract: It is now feasible to host basic web services on a smart phone due to the advances in wireless devices and

mobile communication technologies. The market capture of mobile web services also has increased

significantly, in the past years. While the applications are quite welcoming, the ability to provide secure and

reliable communication in the vulnerable and volatile mobile ad-hoc topologies is vastly becoming

necessary. Even though a lot of standardized security specifications like WS-Security, SAML exist for web

services in the wired networks, not much has been analyzed and standardized in the wireless environments.

In this paper we give our analysis of adapting some of the security standards, especially WS-Security to the

cellular domain, with performance statistics. The performance latencies are obtained and analyzed while

observing the performance and quality of service of our Mobile Host.

1 INTRODUCTION

From the view-point of information systems

engineering, the Internet has lead the evolution from

static content to Web Services. Web Services are

software components that can be accessed over the

Internet using well established web mechanisms,

XML-based open standards and transport protocols

such as SOAP (W3C, 2003) and HTTP. Public

interfaces of Web Services are defined and described

using Web Service Description Language (WSDL)

(Christensen, 2001), regardless of their platforms,

implementation details. Web Services have wide

range of applications and primarily used for

integration of different organizations. The biggest

advantage of Web Services lies in their simplicity in

expression, communication and servicing. The

componentized architecture of Web Services also

makes them reusable, thereby reducing the

development time and costs. (Booth, 2004)

Simultaneously, the high-end mobile phones and

PDAs are becoming pervasive and are being used in

wide range of applications like location based

services, banking services, ubiquitous computing

etc. The higher data transmission rates achieved in

wireless domains with 3G (3GPP, 2006) and 4G

(Thomas, 1999) technologies also boosted this

growth in the cellular market. The situation brings

out a large scope and demand for software

applications for such high-end mobile devices.

To meet this demand of the cellular domain and

to reap the benefits of the fast growing web services

domain and standards, the scope of the mobile

terminals as both web services clients and providers

is being observed. While mobile web service clients

are common these days, we have studied the scope

of mobile web service provisioning. The details of

our Mobile Host and its performance analysis are

available at (Srirama, 2006a).

While service delivery and management from

Mobile Host is technically feasible, the ability to

provide secure and reliable communication in the

vulnerable and volatile mobile ad-hoc topologies

vastly becomes necessary. Moreover with the easily

readable mobile web services, the complexity to

realize security increases further. For the traditional

wired networks and web services, a lot of

standardized security specifications, protocols and

implementations like WS-Security (Lawrence,

2004), SAML (Mishra, 2005) etc., exist, but not

much has been explored and standardized in wireless

environments. Some of the reasons for this poor

state might be the lack of active commercial data

applications due to the limited resource capabilities

of the mobile terminals.

386

Narayana Srirama S., Jarke M. and Prinz W. (2007).

A PERFORMANCE EVALUATION OF MOBILE WEB SERVICES SECURITY.

In Proceedings of the Third International Conference on Web Information Systems and Technologies - Internet Technology, pages 386-392

DOI: 10.5220/0001276603860392

 SciTePress

Our study contributes to this work and tries to

bridge this gap, with main focus at realizing some of

the existing security standards in the mobile web

services domain. In this study, we have analyzed the

adaptability of WS-Security in the mobile web

services domain. Mainly we observed the latency

caused to performance of the Mobile Host, with the

introduction of security headers into the exchanged

SOAP messages. Performance penalties of different

encryption and signing algorithms were calculated,

and the best possible scenario for securing mobile

web services communication is suggested.

The rest of the paper is organized as follows:

Section 2 discusses the standards and on going

projects for securing mobile web services domain.

Section 3 addresses our security analysis setup and

test cases. Section 4 summarizes the results and the

means of securing mobile web services. Section 5

concludes the paper with future research directions.

2 SECURING MOBILE WEB

SERVICE COMMUNICATION

Mobile web service messages are exchanged using

the SOAP over different transportation protocols

like HTTP, UDP, and WAP etc. SOAP by itself does

not specify the means of providing the security for

the web service communication. Also many

legitimate intermediaries might exist in the web

service communication making the security context

requirement to be from end-to-end. Hence the

traditional point-to-point security technologies like

the SSL, HTTPS and full encryption provided by the

3G technologies like UMTS communication

technology (Umtsworld, 2002) can’t be adapted for

the mobile web services domain. These methods

also affect the transport independency feature of the

SOAP messages by restricting the messages to

particular transportation protocols.

For securing the wired web services, OASIS has

developed different protocols like WS-Security and

SAML using and extending the W3C protocols and

standards SOAP, XML Encryption (Reagle, 2001),

XML Signature (Eastlake, 2002) and WSDL. WS-

Security and SAML protocols make use of the

composable and extendable nature of SOAP and

embed the security information into SOAP headers.

2.1 WS-Security

The WS-Security specification from OASIS is the

core element in web service security realm. It

provides ways to add security headers to SOAP

envelopes, attach security tokens and credentials to a

message, insert a timestamp, sign the messages, and

encrypt the message. The protocol ensures

authentication with security tokens. Security tokens

in combination with XML Encryption ensure

confidentiality while security tokens in combination

with XML Digital Signatures ensure integrity, of the

SOAP messages.

SOAP Foundation

WS-Security

WS-Policy WS-Trust WS-Privacy

WS-

SecureConversation

WS-Federation WS-Authorization

SOAP FoundationSOAP Foundation

WS-Security

WS-Policy WS-Trust WS-Privacy

WS-

SecureConversation

WS-Federation WS-Authorization

Figure 1: Web Service Security specifications.

Apart from WS-Security, web service security

specifications also include WS-Policy which defines

the rules for service interaction, WS-Trust which

defines trust model for secure exchanges and WS-

Privacy which states the maintenance of privacy of

information. Built with these set of basic

specifications are the specifications, WS-

SecureConversation that specifies how to establish

and maintain secured session for exchanging data,

WS-Federation which defines rules of distributed

identity and its maintenance, and WS-Authorization

specification which processes the access rights and

exchangeable information. The web service security

specifications are shown in figure 1. (IBM, 2002)

2.2 SAML

Security Assertion Markup Language (SAML) from

OASIS primarily provides single sign on (SSO),

cross domain interoperability, means of

implementing the basic WS-Security standard

through assertions, and helps in managing identity

control across domains and organizations. SAML

builds on top of the web service security

specifications and provides a means by which

security assertions can be exchanged between

different service entity endpoints.

The basic components of interest in SAML are

assertions, protocols, bindings and profiles. SAML

Assertions carry the authentication information

while SAML Request/Response protocols tell how

and what assertions can be requested. Bindings

define the transportation of SAML protocols over

SOAP/HTTP protocol. A SAML profile can be

created using the bindings, protocols along with the

A PERFORMANCE EVALUATION OF MOBILE WEB SERVICES SECURITY

387

assertion structure. The SAML Request or SAML

Response will reside in SOAP Body.

SAML Request/Response protocol binding over

SOAP will provide Assertions in the SOAP Body

with information about authentication and

authorization. Then SAML Assertions are used

along with the WS security element which will

reside in SOAP Header. As the SAML Assertions

contain key of the holder, it can be used to digitally

sign the SOAP Body. At the Receiver end, the

signature is verified with the help of the key and the

access controls within the Assertion.

2.3 LA

Liberty Alliance project (LA, 2006) is the only

global body which is working to define and provide

technology, knowledge and certifications to build

identity into the foundations of mobile and web

service communication. It mainly concentrated on

federated identity, because of the lack of

connectivity between identities for internet

applications in the current wireless technology

especially in mobile networks.

The basic components of Liberty Alliance are

principal, identity provider and service provider.

Principal is the requestor who needs to be

authenticated. Identity provider is the one which

authenticates and asserts the principal’s identity. The

basic provisions of this project are federation which

establishes relationship between any two of the

above mentioned components, Single Sign On

(SSO) where the authentication provided to principal

by the identity provider can be maintained to other

components such as service providers, and circle of

trust where trust will be established between service

providers and identity providers with agreements

upon which principals can make transactions and

exchange information in a seamless and secure way.

3 EVALUATION OF

WS-SECURITY FOR SMART

PHONES

To secure the communication of our mobile web

services provisioning, we have analyzed the

adaptability of WS-Security in the mobile web

services domain (Srirama, 2006b). The WS-Security

adds many performance overheads to the mobile

web service invocation cycle. Mainly, extra CPU

capabilities are required to process the WS-Security

related header elements. The transportation delays

also increase significantly as the SOAP message size

increases with the added security headers.

During our performance analysis of the Mobile

Host, we have observed that the transmission delays

sum up to 90% of the total mobile web service

invocation cycle times, in GPRS (GSMWorld, 2006)

environment. The best solution to cope with this

problem would be to increase the transmission

capabilities of the wireless networks. With the

introduction of 3G technologies like UMTS which

promises a data transmission rate of approximately 2

Mbps and the 4G announcement (4GPress, 2005) of

achieving the 2.5 Gbps should make the

transmission problem void. When such networks are

adapted, the increase in the size of the message with

security headers is not the major concern.

To evaluate the WS-Security, we observed the

latency caused to the performance of the Mobile

Host, with the introduction of security headers. The

performance penalties of different encryption and

signing algorithms were calculated at the smart

phone, and the best possible scenario for securing

mobile web services communication is observed.

3.1 Test Setup

The test setup used for WS-Security evaluation is

shown in figure 2. The Mobile Host was developed

and deployed on a smart phone. The mobile web

service client invokes different web services

deployed with the Mobile Host. The Mobile Host

processes the service request and sends the response

back to the client. The performance of the Mobile

Host and the network latency were observed while

processing the client request.

WSWS

Internet

Mobile

Infrastructure

Mobile

Infrastructure

Mobile Host

WS Client

Identity Provider

WSWS

Internet

Mobile

Infrastructure

Mobile

Infrastructure

Mobile Host

WS Client

Identity Provider

Figure 2: Mobile web service invocation test setup.

For the test cases, generating the security keys at

the smart phones was observed to be beyond their

low resource capabilities. It was observed that the

time taken for generating keys, especially PKI based

asymmetric keys is very high. The times were in the

order of 1-3 minutes and were highly unpredictable.

Hence a standalone end-point security provider

(Identity Provider) was used to provide the keys and

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security information for the secured mobile web

service communication. The keys are obtained by

connecting to the identity provider across the mobile

operator proprietary network and the Internet. The

identity provider also helps in achieving SSO. The

security assertions and keys were exchanged with

the identity provider according to LA standards.

For the analysis, two SonyEricsson P910i smart

phones were used as web service requestor and

Mobile Host. The smart phones had an internal

memory of 64 Kb and ARM9 processor clocked at

156MHz. The phones were connected to the Internet

using a GPRS connection. The Mobile Host and

client were developed using J2ME MIDP2.0

(JSR118, 2002) with CLDC1.0 (JSR139, 2002)

configuration. For cryptographic algorithms and

digital signers, java based light weight cryptographic

API from Bouncy Castle crypto package

(BouncyCastle, 2006) was used. kSOAP2

(KSOAP2, 2006) was modified and adapted

according to WS-Security standard and utilized to

create the request/response web service messages.

3.2 Test Cases

Many basic services like the picture service, location

data provisioning service, dir service and etc., were

provided by the Mobile Host. For the test case

analysis of security, addressed in this paper, we

considered the location data provisioning service.

The service provides the location details of the

Mobile Host as GPS information. The smart phone

connects to a socket based GPS device via Bluetooth

for fetching the GPS co-ordinates. To observe the

performance penalties for different message sizes,

the request contained the <responseSize> element,

which specifies the response size of the message

being expected in Kb. The response was also added

with an extra element <bodyPadding> to fill the

remaining size of the response. The typical request

and response of the service are shown in figure 3.

<soapenv:Envelope xmlns:soapenv="..."

xmlns:xsd="..." xmlns:xsi="...">

<soapenv:Body>

<GPSProvider soapenv:encodingStyle

="...">

1 </responseSize>

</GPSProvider>

</soapenv:Body>

</soapenv:Envelope>

<SOAP-ENV:Envelope ...>

<SOAP-ENV:Body ...>

<GPSProvider xmlns="ssn:SSNServer"

id="o0" SOAP-ENC:root="1">

606428</Longtitude>

</Comment>

</result>

<Request-ID ...>2</Request-ID>

...</bodyPadding>

</GPSProvider>

</SOAP-ENV:Body>

</SOAP-ENV:Envelope>

Figure 3: Request and response messages of the location

data provisioning service, respectively.

To achieve confidentiality, the SOAP messages

were ciphered with symmetric encryption algorithms

and the generated symmetric keys were exchanged

by means of asymmetric public key infrastructure

(PKI) based methods. The messages were tested

against various symmetric encryption algorithms,

along with the WS-Security mandatory algorithms,

TRIPLEDES, AES-128, AES-192 and AES-256.

(RSA Labs, 2006) RSA with 1024 and 2048 bit keys

was used for key exchange. Upon successful

analysis of confidentiality, we tried to ensure data

integrity of the messages. The messages were

digitally signed and were evaluated against two

signature algorithms, DSAwithSHA1 (DSS) and

RSAwithSHA1 with 1024 and 2048 bit keys. The

effect of signing on top of encryption was also

studied.

To summarize, the experiments leave us with

four test cases for the analysis of WS-Security for

smart phones.

Unsecured MWS communication

Encrypted MWS communication

Signed MWS communication

Encrypted + Signed MWS communication

Each of these test cases was observed with

different message sizes. The sizes of the response

messages ranged from 1-10Kb. All the experiments

were repeated at least 5 times and the mean of the

values were observed for drawing conclusions, to

have statistically valid results.

A PERFORMANCE EVALUATION OF MOBILE WEB SERVICES SECURITY

389

4 ANALYSIS AND THE RESULTS

A typical web service message after applying the

WS-Security is shown in figure 4. The SOAP

message body can be completely encrypted or only

parts of the message can be encrypted. The ciphered

data is stored in the body of the updated message.

The security information like encryption algorithms

used, keys, digests, signing information is

maintained in the SOAP header. The message shown

below is the snapshot of a message encrypted with

AES, and the key exchanged with RSA V 1.5. The

message was later signed with RSAwithSHA1.

<v:Envelope ...>

<v:Header>

<n1:EncryptedKey ...>

<EncryptedMethod

Algorithm="...#rsa-1_5" />

</ReferenceList>

</n1:EncryptedKey>

<n2:Signature ...>

<SignedInfo> <SignatureMethod

Algorithm="...#rsa-sha1" />

<Reference> <DigestMethod

Algorithm="...#sha1" />

</Reference>

</SignedInfo>

...</SignatureValue>

</RSAKeyValue> </KeyValue>

</KeyInfo>

</n2:Signature>

</Security>

</v:Header>

<v:Body>

<n0:EncryptedData Id="223940028" ...>

<EncryptionMethod

Algorithm="...#AESEngine" />

</CipherData>

</n0:EncryptedData>

</v:Body>

</v:Envelope>

Figure 4: A typical SOAP message with WS-Security.

The example shown in figure 4 also hints the

increase in size of the message with the added

security header information. With our analysis we

have observed that there is a linear increase in the

size of the message with the security incorporation.

Table 1 shows the variations in mobile web service

message size with the applied security. The latency

in the encrypted message size for a typical 5 Kb

message is approximately 50%.

Table 1: Message size variations (in bytes) with security.

Original message

size

1024 2048 5120 10240

Message size

with Signature

1726 2750 5822 10942

Encrypted

message size

1804 3168 7264 14092

Secured message

size

2611 3975 8071 14899

4.1 Encrypted Mobile Web Service

Communication

To analyze the effects of XML Encryption on the

mobile web service invocation cycle, the messages

were encrypted with IDEA with 128 and 256 bit

keys, DES with 64 and 192 bit keys and AES with

128, 192 and 256 bit keys. The keys were exchanged

using RSA with key sizes 1024 and 2048 bits.

Figure 5 summaries the results of our encryption

analysis and shows the comparison of latency for

different encryption algorithms with keys exchanged

using RSA 1024. To get the exact performance

penalties and to exclude the transmission delays, the

invocation cycle was observed on one smart phone.

718

2004

2224

1939

2101

2223

2036

2146

847

2466

2547

2236

2437

2310

2358

2470

938

2514

2617

2328

2498

2388

2426

2498

1110

2581

2694

2485

2723

2644

2647

2692

500

1000

1500

2000

2500

3000

Security

IDEA-128 IDEA-256 DES-64 DES-192 AES-128 AES-192 AES-256

Transmission latencies (in milliseconds)

1 KB message 2 KB message 5 KB message 10 KB message

Figure 5: Performance latencies with various symmetric

key encryption algorithms and exchanging keys with RSA

1024.

The results suggest that AES 192 encryption

turns out be the best symmetric key encryption

method. But the difference in latencies with AES

192 and AES 256 are not so significant. So the best

means of encrypting the message would be to use

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AES 256 bit key and to exchange the message with

RSA 1024 bit key, both in terms of provided

security and performance penalty. Still the increased

latency with this best scenario is approximately 3

times the latency without any security. The extra

delays mainly constitute the times taken for

encryption of request at the client, the decryption of

request at the Mobile Host, the encryption of

response at the Mobile Host and the decryption of

response at the client. RSA 2048 key exchange was

beyond the resource capabilities of smart phones.

The results clearly reveal that the processing

capabilities of today’s smart phones are not yet

sufficient for providing proper message level

security for mobile web services. Yet the

performance penalties are well with in limits, ~= few

seconds, and the approach can be used in providing

proper security for mobile web services.

4.2 Signed Mobile Web Service

Communication

To analyze the effects of XML digital signatures on

the mobile web service invocation cycle, the

messages were signed with two signature

algorithms, DSAwithSHA1 (DSS) and

RSAwithSHA1 with 1024 and 2048 bit key sizes.

The latencies are shown in figure 6.

699

825

942

1123

2191

2214

2359

2537

2237

2497

2807

3855

500

1000

1500

2000

2500

3000

3500

4000

4500

1 KB message 2 KB message 5 KB message 10 KB message

Me ssa ge si z e s

Transmission latencies (Milliseconds)

No Security RSA-1024 DSA-1024

Figure 6: Performance latencies with signing the web

service messages.

The results suggest that the best way to sign the

mobile web service message would be using RSA

V1.5 with 1024 bit key. RSA algorithm is preferred

ahead of the DSA, considering performance

latencies. With a key size greater than 1024, signing

is also beyond the resource capabilities of the smart

phone, similar to asymmetric key exchange, using

any of the considered algorithms. It was also

observed that the latency by signing is slightly

higher than the latency caused by the encryption,

especially, when considering DSS signature.

4.3 Secured Mobile Web Service

Communication

In real-time applications, to obtain the maximum

security and to achieve confidentiality and integrity,

both encryption and signing will be used on the

messages. So, after the initial individual analysis of

encryption and signing, we have checked the

latencies for signing on top of encryption. Figure 7

shows the latencies with the complete security

applied on the mobile web service messages. The

results are for a mobile web service message of

request size 1 KB and response size 2 KB.

Symmetric Encryption Algorithms Analysis

(Key exchange with RSA-1024 bit)

3356

3491

3634

3375

3626

3441

3275

5457

5444

5705

5535

6127

5571

5688

1000

2000

3000

4000

5000

6000

7000

IDEA-128 IDEA-256 DES-64 DES-192 AES-128 AES-192 AES-256

Algorithms with key sizes

Time in milliseconds

RSA Signature DSA Signature

Figure 7: Performance latencies with signing on top of the

encryption.

From the test results we can conclude that the

best way of securing messages in mobile web

service provisioning is to use AES symmetric

encryption with 256 bit key, and to exchange the

keys with RSA 1024 bit asymmetric key exchange

mechanism and signing the messages with

RSAwithSHA1. RSA’s consideration for signing is

not just based on the increased latencies of DSS, but

also depended on the asymmetric key exchange

mechanism considered. As we were using the RSA

for key exchange mechanism, the keys can be reused

for signing in the complete secured scenario. This

saved us some initializations and thus reduced the

latency in the RSA signature test cases.

But there are still high performance penalties

when the messages are both encrypted and signed.

So we suggest encrypting only the parts of the

message, which are critical in terms of security and

signing the message. The signing on top of the

encryption can also be avoided in specific

applications with lower security requirements.

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5 CONCLUSIONS

The paper summarizes our comprehensive study on

analyzing the security for mobile web services

provisioning. In this paper we included our analysis

of adapting the wired web service security

specifications to the cellular world, with

performance statistics. The results of our study are

welcoming and the mobile web service messages of

reasonable size, approximately 2-5kb, can be

secured with standard specifications. But based on

our till-date realization of security awareness in

cellular networks, we conclude that secure web

service provisioning in mobile networks is still a

great challenge. The mechanisms developed for

traditional networks are not always appropriate for

the mobile environment and support at hardware like

adding an encryption chipset is recommended.

Our future research in this domain includes

providing proper end-point security for the Mobile

Host with federated identity and appropriate SSO

strategy, using SAML and LA standards. We also

want to have a detailed performance analysis of the

Mobile Host with full security features through real-

time applications. We are also looking for

alternatives, to reduce the security processing load

on the Mobile Host using Enterprise Service Bus

(ESB) (Borck, 2005) based mediation framework for

maintaining the QoS of the Mobile Host.

The increase in size of the message with the

security headers is also quite daunting. We are

currently focusing at XML compression and SOAP

optimization techniques, to reduce the size of the

message, there by improving the scalability of the

Mobile Host. The scalability can also be maintained

as part of QoS at the mediation framework.

ACKNOWLEDGEMENTS

The work is supported by German Research

Foundation (DFG) as part of the Graduate School

”Software for Mobile Communication Systems” at

RWTH Aachen University. The authors also thank

R. Levenshteyn and M. Gerdes of Ericsson Research

and K. Pendyala for their help and support.

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