the static identity of the login request message, the adversary may have the chance to reveal the
privacy information about the special user, such as the location information, shopping habits, which
leads to the ID theft attack. Dynamic identity-based user authentication scheme can resolve this
problem, where the user has a fixed identity, and the identity in each login request message is
generated from the fixed identity and dynamically changed for each session. Therefore, the
adversary cannot confirm which user login to the server from the login request message, and many
researchers focus on dynamic identity-based user authentication schemes. In 2004, Das et al. [9]
proposed a dynamic identity-based remote user authentication scheme. In their scheme, the user’s
identities are dynamically changing for each session to avoid the identification theft, and one
dynamic identity is only valid for the current session. However, Awashti [10], Chien and Chen [11],
Liao et al. [12], and Ku and Chen [13] pointed out the security flaws of the scheme of Das et al.
[9], respectively, that is, the scheme of Das et al. [9] did not fulfill the basic needs of authentication
schemes, cannot protect the user’s anonymity, and vulnerable to guessing attack and impersonation
attack. Recently, Wang et al. [14] pointed out that the scheme of Das et al. [9] was completely insecure
because the authentication is independent to the passwords. In addition, the scheme of Das et al. [9] did
not provide mutual authentication and susceptible to the server spoofing attack. Later, Wang et al.[14]
proposed a dynamic identification-based remote user authentication scheme, and they claimed that
their scheme was more efficient and secure than the scheme of Das et al. [9]. However, Chang and
Chang et al. [15], Yeh et al. [16], and Khan et al. [17], respectively, pointed out the security
weaknesses of the scheme of Wang et al. [14], that is, the scheme of Wang et al. [14] was vulnerable
to the password guessing attack, masquerade attack, denial of service attack, and identification theft
attack. Most recently, Chang et al. [18] found that the scheme of Wang et al. [14] was traceable of
the identity of the users and the password change was unverifiable. Then, they presented an
untraceable dynamic identity-based remote user authentication scheme with the verifiable password
update. However, in this paper, we will point out that the scheme of Chang et al. [18] cannot achieve
the property of untraceability, and any malicious registered user can easily reveal the other user’s
identity from the eavesdropped session message. Besides, we find the scheme of Chang et al.[18]
vulnerable to offline password guessing attack, impersonation attack, stolen smart card attack, and
insider attack. At last, the scheme of Chang et al. [18] exists the clock synchronization problem,
and it is inef
ficient in password verification and password update.
The rest of this paper is organized as follows. In Section 2, we briefly review the scheme of
Chang et al. [18]. Section 3 discusses the weaknesses of the scheme of Chang et al. [18]. At last,
we give some conclusions in Section 4.
2. OVERVIEW OF THE SCHEME OF CHANG ET AL.
In order to facilitate the analysis of the scheme, we review the scheme of Chang et al. [18] in this
section. The notations used in the scheme of Chang et al. [18] are listed in Table I. The scheme of
Chang et al. [18] contains four phases, that is, the registration phase, the login phase, the
Table I. Notations.
Notation Description
U
i
/U
a
A system user/an attacker
S The remote server
ID
i
, PW
i
, PW
i
new
U
i
’s identity, password, and new password, respectively
CID
i
The dynamic identity of U
i
T, T′, T″ Timestamps
ΔT The expected valid time interval
h(·) A secure one-way hash function
⊕ An XOR operation
x A secret key of S
y A secret number of S
|| A concatenation operation
375CRYPTANALYSIS OF A DYNAMIC IDENTITY-BASED USER AUTHENTICATION SCHEME
Copyright © 2013 John Wiley & Sons, Ltd. Int. J. Commun. Syst. 2015; 28:374–382
DOI: 10.1002/dac