3. MOBILE COMMERCE SECURITY
Secure commercial
information exchange and safe electronic financial transactions are
essential for both service providers and potential customers. Various
mobile security procedures have therefore been proposed and applied to
mobile commerce. A secure mobile commerce system must have the following
properties: (i) confidentiality, (ii) authentication, (iii) integrity,
(iv) authorization, (v) availability, and (vi) non-repudiation. This
section discusses the security issues related to the following three
network paradigms: (i) wireless local area networks, (ii) wireless wide
area networks, and (iii) WAP. The future of mobile commerce depends on
its ability to securely and safely exchange information between mobile
users and content providers. However, applying the security and payment
technologies originally designed for electronic commerce to mobile
commerce has been less than helpful because electronic commerce and
mobile commerce are based on fundamentally different infrastructures
(wired versus wireless). A wide variety of security procedures have
therefore been developed specifically for mobile commerce. These
technologies are extremely diverse and complicated and a comprehensive
discussion concerning them is still awaited. Mobile commerce
applications are built on top of the existing network infrastructure of
wired networks, such as the Internet; wireless networks, such as wide
area 3G cellular networks; and Wi-Fi wireless local area networks
(WLAN). Therefore, security issues in mobile commerce are tightly
coupled with network security.
Properties and Requirements of Mobile Commerce Security
First and foremost, the theme of this section,
mobile commerce security, is defined as the technological and managerial
procedures applied to mobile commerce transactions to provide the
following functions for mobile commerce data and systems:
Confidentiality: The information and systems must not be disclosed to unauthorized persons, processes, or devices.
Authentication: This ensures that parties to a transaction are not impostors and are trustworthy.
Integrity: The information and systems have not been altered or corrupted by outside parties.
Authorization: Procedures must be provided to verify that the user can make the requested purchases.
Availability: An authorized user must have timely, reliable access to information in order to perform mobile commerce transactions.
Non-repudiation:
Ensures a user cannot deny they performed a transaction; the user is
provided with proof of the transaction and the recipient is assured of
the user's identity.
These procedures involve a variety of policies
and processes, along with the hardware and software tools necessary to
protect the mobile commerce systems and transactions and the information
processed, stored, and transmitted by them.
It is first necessary to examine what kind of
features mobile commerce security and payment methods are expected to
have in order to conduct effective and efficient mobile commerce
transactions and what kind of challenges may be faced in the process of
developing new mobile commerce security and payment methods. The
requirements for mobile commerce security include:
Confidentiality, authentication, integrity, authorization, availability, and non-repudiation must be rigorously enforced.
They should be interoperable for most systems.
They should be acceptable for both current and future systems at minimal cost.
They should allow content providers to provide affordable, easy-to-use, efficient and interoperable payment methods to users.
No mobile commerce transactions are deferred or deterred because of their deployment.
Security Basics
Without confidence in the security of the
underlying networking technologies, mobile commerce will be
unimaginable. Network security usually involves communications between
two or more participating entities, but the term "security" covers many
different aspects. In this section we will focus on those features that
are most important to mobile commerce systems.
Security Services
A mobile commerce system needs to provide
security services to its participating entities so that business can be
conducted successfully in electronic form. These security services
include:
Authentication.
Before business transactions can be performed, the participating
entities (usually the sender and receiver) must confirm each others'
identities. This service prevents an unauthorized third-party from
masquerading as one of the legitimate parties. Authentication is usually
achieved using network-based authentication protocols.
Data confidentiality/secrecy.
In an electronic business transaction, it is assumed that only the
sender and intended receiver(s) will be able to read the transmitted
messages in cleartext. Providing data confidentiality prevents
eavesdroppers or interceptors from understanding the secret
communication. This is usually accomplished using computer-based
cryptographic encryption and decryption computation.
Data integrity.
It should not be possible for a transmitted message to be altered,
whether accidentally or maliciously, without this being detected at the
receiver side of a mobile commerce system. With this security feature,
an interceptor is not able to deceive the receiver by modifying the
content of a message in transmission. Adding secure electronic
signatures to messages provides data integrity.
Non-repudiation.
Mobile commerce transactions are official business deals. Neither the
sender nor receiver should be able to deny the existence of a legitimate
transaction afterwards. That is, the sender must be able to prove that
the specified receiver received the message and the receiver must be
able to prove that the specified sender did in fact send the message.
This is usually done using digital signature techniques.
Availability.
The availability of a mobile commerce system ensures that legitimate
users can access the business service reliably and securely. The system
should be designed to minimize the impact of events such as malicious
denial-of-service (DoS) attacks, which can cause mobile commerce
services to become unstable or unusable for long periods of time.
Deploying network security devices such as firewalls and configuring
them along with associated protocols properly is the key to ensuring
service availability.
Security Mechanisms
Security services in the modern world must take
advantage of the latest advances in computation technology, both
hardware and software. To achieve these security goals, digital data are
encrypted and decrypted based on cryptographic algorithms. There are
two categories of cryptographic algorithms: symmetric key systems and
asymmetric key systems.
Symmetric key systems.
In this category, the sender and receiver participating in a secure
session both own the same digital key. The sender encrypts messages
using this key and then sends it to the receiver through the public
network. The receiver then decrypts the messages received using the same
key. This digital key, however, is never transmitted over the network
in cleartext, thus preventing a third-party from obtaining it and thus
compromising the secure communication. To agree upon this symmetric key
requires both sides to use outside channels, such as a telephone
conversation, or a specially designed key distribution center (KDC). The
data encryption standard (DES), triple-DES (3DES), and advanced
encryption standard (AES) are symmetric key systems.
Asymmetric key systems.
These are also called "public key systems." Unlike in symmetric key
systems, a participating entity in an asymmetric key system uses two
keys-a public key that is accessible to everyone in the world and a
private key known only to itself. Applying one or both of these two keys
in different orders to data messages provides security services such as
authentication and digital signature. The famous RSA algorithm is an
example of an asymmetric key system.
Mobile Security
As discussed earlier, mobile security is a
crucial issue for mobile commerce. From a technical point of view,
mobile commerce over wireless networks is inherently insecure compared
to electronic commerce over wired networks. The reasons are as follows:
Reliability and integrity:
Interference and fading make the wireless channel inherently error
prone. Frequent handoffs and disconnections also degrade the security of
wireless services.
Confidentiality/Privacy:
The broadcast nature of the radio channel makes it easier for an
outsider to tap into. Thus, communication can be intercepted and
interpreted without difficulty if security mechanisms such as
cryptographic encryption are not employed.
Identification and authentication: The mobility of wireless devices introduces an additional difficulty in identifying and authenticating mobile terminals.
Capability:
Wireless devices usually have limited computation capability, memory
size, communication bandwidth, and battery power. This makes it
difficult to utilize high-level security schemes such as 256-bit
encryption.
Security issues span the whole mobile commerce
system, from one end to the other, from the top to the bottom network
protocol stack, from machines to humans. We will focus only on issues
exclusively related to mobile/wireless technologies. Lacking a unified
wireless security standard, different wireless technologies support
different aspects and levels of security features. We will thus discuss
some well-known wireless network standards and their corresponding
security issues.
Network Infrastructure and Security
Network infrastructure provides essential voice
and data communication capability for consumers and vendors in
cyberspace. When progressing from electronic commerce (EC) to mobile
commerce (MC), it is necessary for a wired network infrastructure such
as the Internet to be augmented by wireless networks that support
mobility for end users. Mobile commerce is possible mainly because of
the availability of wireless networks. User requests are delivered to
either the closest wireless access point (in a wireless local area
network environment) or abase station (in a cellular network
environment). Although the wired network is not essential in a mobile
commerce system, most mobile commerce servers reside on wired networks
and user requests are frequently routed to these servers using transport
and/or security mechanisms provided by wired networks. However our
focus in this section is on the unique aspects of the mobile commerce
network infrastructure, which is by definition a wireless mobile
network, therefore we have chosen to omit any discussion of wired
networks.
Wireless communication capability supports
mobility for end users in mobile commerce systems. Wireless LAN and WAN
are major components used to provide radio communication channels so
that mobile service is possible. In the WLAN category, the Wi-Fi
standard with 11 Mbps throughput dominates the current market, although
it is expected that standards with much higher transmission speeds, such
as IEEE 802.11a and 802.11g, will replace Wi-Fi in the near future.
Cellular networking technologies are advancing at a tremendous pace and
each represents a solution for a certain phase, such as 1G, 2G, and 3G,
in a particular geographical area, such as the United States, Europe, or
Japan. Compared to WLANs, cellular systems can provide longer
transmission distances and greater radio coverage, but suffer from the
drawback of much lower bandwidth (less than 1 Mbps). In the latest trend
for cellular systems, 3G standards supporting wireless multimedia and
high-bandwidth services are beginning to be deployed. WCDMA and CDMA2000
are likely to dominate the market in the future.
Wireless Local Area Networks and Security
The major WLAN standards are shown in Table 2. Security issues specific to WLANs can be dealt with in two ways:
Wi-Fi security.
The security provisions in the IEEE 802.11 WLAN standard are based on
the use of a data link level protocol called Wired Equivalent Privacy
(WEP). When it is enabled, each mobile host has a secret key that is
shared with the base station. The encryption algorithm used in WEP is a
stream cipher based on RC4. The ciphertext is generated by XORing the
plaintext with a RC4 generated keystream. However, recently published
literature has discovered methods for breaking this approach . The next version, 802.11i, is expected to have better security.
Bluetooth security.
Bluetooth provides security by using frequency hopping in the physical
layer, sharing secret keys (called passkeys) between the slave and the
master, encrypting communication channels, and controlling integrity.
Encryption in Bluetooth is a stream cipher called "E0", while for integrity control a block cipher called "SAFER+" is used. However, "E0" has potential weaknesses and "SAFER+" is slower than the other similar symmetric-key block ciphers.
Wireless Wide Area Network and Security
As discussed earlier, the most important
technology in this category is the cellular wireless network. GSM and
UTMS systems use different approaches to deal with security issues.
GSM security.
The Subscriber Identity Module (SIM) in the GSM contains the
subscriber's authentication information, such as cryptographic keys, and
a unique identifier called international mobile subscriber identity
(IMSI). The SIM is usually implemented as a smart card consisting of
microprocessors and memory chips. The same authentication key and IMSI
are stored on GSM's network side in the authentication center (AuC) and
home location register (HLR), respectively. In GSM, short messages are
stored in the SIM and calls are directed to the SIM rather than the
mobile terminal. This feature allows GSM subscribers to share a terminal
with different SIM cards. The security features provided between GSM
network and mobile station include IMSI confidentiality and
authentication, user data confidentiality, and signaling information
element confidentiality. One of the security weaknesses identified in
GSM is the one-way authentication utilized, where only the mobile
station is authenticated and the network is not. This can pose a
security threat, as a compromised base station can launch a
"man-in-the-middle" attack without being detected by mobile stations.
UMTS security.
UMTS is designed to reuse and evolve from existing core network
components of the GSM/GPRS and fix known GSM security weaknesses such as
the one-way authentication scheme and optional encryption.
Authentication in UMTS is mutual and encryption is mandatory (unless
specified otherwise) in order to prevent message replay and
modification. In addition, UMTS employs longer cryptographic keys and
newer cipher algorithms, which make it inherently more secure than
GSM/GPRS.
WAP and Security
Beyond the link-layer communication mechanisms
provided by WLANs and cellular networks, the Wireless Application
Protocol (WAP) is designed to work with all wireless networks. The most
important technology applied by WAP is probably the WAP Gateway, which
translates requests from the WAP protocol stack to the WWW stack so they
can be submitted to Web servers. For example, requests from mobile
stations are sent as a URL through the network to the WAP Gateway;
responses are sent from the Web server to the WAP Gateway in HTML and
are then translated to WML and sent to the mobile stations. Although WAP
supports HTML and XML, its host language is WML (Wireless Markup
Language), which is a markup language based on XML that is intended for
use in specifying content and user interfaces for mobile stations. WAP
also supports WMLScript, which is similar to JavaScript but makes
minimal demands on memory and CPU power because it does not contain many
of the unnecessary functions found in other scripting languages.
WAP security is provided
through the Wireless Transport Layer Security (WTLS) protocol (in WAP
1.0) and IETF standard Transport Layer Security (TLS) protocol (in WAP
2.0). They provide data integrity, privacy, and authentication. One
security problem, known as the "WAP Gap" is caused by the inclusion of
the WAP gateway in a security session. That is, encrypted messages sent
by end systems might temporarily become clear text on the WAP gateway
when messages are processed. One solution is to make the WAP gateway
resident within the enterprise (server) network , where heavyweight security mechanisms can be enforced.
