Secure communication for electronic business applications in mobile agent networks


Secure communication for electronic business applications in mobile
agent networks

Woei-Jiunn Tsaur
Department of Information Management, Da-Yeh University, Changhua 515, Taiwan

a r t i c l e i n f o

Keywords:
Mobile agent
Electronic business applications
Smart card
Proxy signature
Network security

a b s t r a c t

The mobile agent plays an increasingly important role in electronic business applications, because it can
provide the essential properties of personalization, automation and intelligence, etc. This paper proposes
several appropriate security schemes for protecting mobile agent networks in electronic business appli-
cations. As far as mobile agent security is concerned, we develop a proxy signature scheme for protecting
mobile agents against malicious agent hosts. The proposed proxy signature scheme can protect users’ pri-
vate keys stored in smart cards, and provide the fairness of contracts signed by agents. In addition, we
also design a proxy authenticated encryption scheme so that the signature of the contracts will satisfy
users’ constraints, and the non-repudiation of servers can be achieved. On the other hand, as far as agent
host security is concerned, we apply the idea of proxy signature to construct an authentication scheme
for protecting agent hosts. This scheme is to achieve the requirements of authentication and authoriza-
tion. Furthermore, we also implement the proposed security schemes to achieve security requirements of
confidentiality, integrity, authenticity, and non-repudiation for protecting Linux-based mobile agents and
hosts in an electronic auction application. Hence, we affirm that the proposed security schemes are suit-
able for practical electronic business applications in mobile-agent-based network environments.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

In recent years, there are many business applications based on
mobile agent on a variety of networks (Benouhiba & Nigro, 2006;
Kang, Lee, & Choi, 2008; Kim, Kwon, & Kwak, 2010; Park, Kang, &
Kim, 2006; Wu et al., 2010; Yun, Lee, Yu, & Choi, 2009). The agents
of the business applications usually provide personalization, auto-
mation and intelligence, etc. However, it also results in many secu-
rity threats such as stealing data from hosts by agents and
tampering constraints of agents by hosts. For instance, when a mo-
bile agent carrying a user’s private key roams among servers on
the Internet, the agent may find a bid satisfies the user’s constraints,
and then sign the bid (Chess et al., 1995; White, 1994). However,
users will not wish to equip agents with their private signature keys
when the agents may execute on untrusted agent hosts (Maes,
Guttman, & Moukas, 1999; Sander & Tschudin, 1998; Takeda, Iino,
& Nishida, 1995). On the other hand, a problem specific to mobile
agents is the protection of the agent platforms running the agents.
A hostile agent can destroy the hard drive, steal data, or do all sorts
of undesirable operations to agent platforms. In this paper we will
develop efficient security schemes based on cryptographic solutions
(Mambo, Usuda, & Okamoto, 1996; Sander & Tschudin, 1998) for
prevention of both agents and hosts tampering.

This paper develops a proxy signature scheme and a proxy
authenticated encryption scheme for protecting mobile agents
against malicious agent hosts using the proposed ECC-based self-
certified public key cryptosystem. The proposed proxy signature
scheme can protect users’ private keys stored in smart cards, and
provide the fairness of contracts signed by agents. The proposed
cryptosystem is constructed using the ECC, and it also integrates
the identity-based public key cryptosystem with the self-certified
public key cryptosystem (Girault, 1992; Petersen & Horster,
1997; Saeednia, 1997, 2003) to provide higher security strength.
Furthermore, based on the proposed cryptosystem, we employ
the proposed proxy signature scheme to further design a proxy
authenticated encryption scheme so that the signature of the con-
tracts will satisfy users’ constraints, and the non-repudiation of
servers can be achieved. In summary, these proposed schemes
are able to accomplish the security requirements of confidentiality,
integrity, authenticity, and non-repudiation for protecting mobile
agents in electronic business applications. On the other hand, this
paper also presents an authentication scheme for protecting mo-
bile agent hosts against unauthorized mobile agents. In such a
scheme, a mobile agent can register once to the system authority
for several services in the mobile-agent-based networks. Finally,
we implement the proposed security schemes for protecting Li-
nux-based mobile agent networks in an electronic auction
application.

0957-4174/$ - see front matter � 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.eswa.2011.07.105

E-mail address: wjtsaur@yahoo.com.tw

Expert Systems with Applications 39 (2012) 1046–1054

Contents lists available at ScienceDirect

Expert Systems with Applications

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / e s w a

http://dx.doi.org/10.1016/j.eswa.2011.07.105
mailto:wjtsaur@yahoo.com.tw
http://dx.doi.org/10.1016/j.eswa.2011.07.105
http://www.sciencedirect.com/science/journal/09574174
http://www.elsevier.com/locate/eswa


The rest of this paper is organized as follows. In Section 2, we
briefly describe the elliptic curve cryptosystems. Section 3 first
develops an efficient public key cryptosystems, and then several
security schemes constructed using it are designed for protecting
mobile-agent-based electronic business applications. In Section 4,
security analyses about attacks on the proposed schemes consoli-
date the feasibility of the schemes. Performance evaluation of the
proposed schemes, which is measured by the required computa-
tional effort and communicational cost, is given in Section 5. In
Section 6, we present the implementation of the proposed schemes
on an electronic auction application. Finally, some concluding re-
marks are presented in Section 7.

2. Elliptic curve cryptosystems (ECC)

Assume that P is a point with order n on an elliptic curve E:
y2 = x3 + ax + b (mod p), where 4a3 + 27b2 – 0 (mod p), and Q is
some other point on the same curve. Let P = (xP, yP), Q = (xQ, yQ),
and P + Q = R = (xR, yR). If xP – xQ, set k ¼

yQ�yP
xQ�xP

; if xP = xQ, set
k ¼ 3x

2
P
þa

2yP
. Then the point R = (xR, yR) can be defined by using the fol-

lowing formulae:

xR ¼ k2 � xP � xQ
yR ¼ðxP � xRÞk � yP

In ECC, the elliptic curve discrete logarithm problem (ECDLP) is to
determine an integer x (0 6 x 6 n � 1) such that Q = x � P if such an
x exists. As long as n and p are large enough, it is computationally
intractable to find x with knowing E, Q, and P. Koblitz (1987) and
Miller (1986) implemented this characteristic to elliptic curve cryp-
tosystems. We need 1024-bit keys when using modular exponenti-
ation schemes, like RSA or ElGamal cryptosystems, but we can get
the same security level only using 160 bits in ECC.

In addition, RSA needs to generate Ni = pi � qi for each user,
respectively; however, ECC generates only fixed public information
stored at SA, and can afterwards uses it repeatedly. Therefore, the
storage cost required by ECC is less than that required by RSA.

3. Security schemes for protecting mobile agent networks

In this section, we first develop an efficient public key crypto-
systems, and then several security schemes constructed using it
are designed for protecting mobile-agent-based electronic busi-
ness applications.

3.1. Initialization

The entities in the system are a system authority (SA), users (Ui),
hosts (Hi), and mobile agents (MA) generated by specific users. We
assume that SA is responsible for key generation and user registra-
tion. We then define the notations used in the proposed schemes
as follows:

� p: a field size, where p is typically either an odd prime or a
power of 2 in general applications, and its length is about 160
bits.
� An elliptic curve E over Fp:

E: y2 = x3 + ax + b, where the two field elements a, b 2 Fp and
4a3 + 27b2 – 0 (mod p), and all the points (x, y), x 2 Fp, y 2 Fp,
on E form the set of E(Fp) containing a point O called the point
at infinity.

� B: a base point of order n over E(Fp), where n is a large prime
(160 bits) and the number of Fp-rational points on E, denoted
by # E(Fp), is divisible by n.
� sSA: SA’s private key, where sSA 2 [2, n � 2].

� PSA: SA’s public key, where PSA = sSA � B (‘‘�’’ means the multiplica-
tion of a number and an elliptic curve point.).
� h( ): a one-way hash function that accepts a variable length

input and produces a fixed length output value j, where
j 2 [2, n � 2] and its length is 160 bits. The one-way hash func-
tion h( ) should satisfy the properties (Harn, 1994) that given
h(x), it is computationally infeasible to find x0 – x such that
h(x0) = h(x), meanwhile, h(x0) – h(x) if and only if x0 – x.
� X(P): output the x-coordinate of point P.

After that, SA publishes E, B, p, n, PSA and h, while keeping sSA
secret.

3.2. The proposed public key cryptosystems

The operations of the proposed public key cryptosystems are di-
vided into two phases: the system setup phase and the key gener-
ation phase.

3.2.1. The system setup phase
SA creates a system public key and some public parameters in

this phase, and then SA releases these parameters. SA randomly
chooses a numbersSA and keeps it secret. Then SA computes the
system public key

PSA ¼ sSA � B

3.2.2. The key generation phase
User Ui and host Hi perform the following steps to register to SA,

and obtain the corresponding public key, respectively. They also
compute their private keys in this phase.

Step 1. Ui and Hi execute the following tasks, respectively:
(1-1) Select an identity information, denoted by Ii.
(1-2) Randomly choose an integer xi 2 [2, n � 2] as the master

key.
(1-3) Compute Zi = h(xikIi) � B
(1-4) Submit {Ii, Zi} to SA.

Step 2. SA executes the following tasks for Ui and Hi,
respectively:

(2-1) Randomly choose a time-variant integer ki 2 [2, n � 2].
(2-2) Compute a public key Pi and its witness wi, where

Pi ¼ Zi þðki � hðIiÞÞ � B ¼ðPix; PiyÞ
wi ¼ ki þ sSA � ðPix þ hðIiÞÞ ðmod nÞ

(2-3) Return {Pi, wi} to Ui and Hi, respectively.
Step 3. Ui and Hi then execute the following tasks, respectively:

(3-1) Calculate their own private keys as

si ¼ wi þ hðxikIiÞ ðmod nÞ

(3-2) Verify the authenticity of Pi by testing if

si � B ¼ Pi þ hðIiÞ � B þ½ðPix þ hðIiÞÞ mod n� � PSA ð1Þ

If the verification result of Eq. (1) is correct, then the partici-
pant’s public key is Pi and the corresponding private key is si;
otherwise, it means that the public key Pi is altered in the
transmission. For the consideration of security, the private key si
is stored in a smart card for subsequent electronic business
applications.

In the following, we show that the private key si and the corre-
sponding public key Pi satisfy Eq. (1).

Theorem 1. User Ui and host Hi can utilize Eq. (1) to verify his/her
public key Pi by himself/herself.

W.-J. Tsaur / Expert Systems with Applications 39 (2012) 1046–1054 1047



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