Figures
Abstract
Biometrics authenticated schemes using smart cards have attracted much attention in multi-server environments. Several schemes of this type where proposed in the past. However, many of them were found to have some design flaws. This paper concentrates on the security weaknesses of the three-factor authentication scheme by Mishra et al. After careful analysis, we find their scheme does not really resist replay attack while failing to provide an efficient password change phase. We further propose an improvement of Mishra et al.’s scheme with the purpose of preventing the security threats of their scheme. We demonstrate the proposed scheme is given to strong authentication against several attacks including attacks shown in the original scheme. In addition, we compare the performance and functionality with other multi-server authenticated key schemes.
Citation: Lu Y, Li L, Yang X, Yang Y (2015) Robust Biometrics Based Authentication and Key Agreement Scheme for Multi-Server Environments Using Smart Cards. PLoS ONE 10(5): e0126323. https://doi.org/10.1371/journal.pone.0126323
Academic Editor: Wen-Bo Du, Beihang University, CHINA
Received: September 17, 2014; Accepted: March 30, 2015; Published: May 15, 2015
Copyright: © 2015 Lu et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Data Availability: All relevant data are within the paper.
Funding: This work was supported by National Natural Science Foundation of China (grant no. 61121061), the Beijing Natural Science Foundation (grant no. 4142016), and the Asia Foresight Program under NSFC Grant (grant no. 61411146001). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Introduction
With the swift development of wireless communications and network technologies, more and more people use wireless handheld devices (e.g.PDA, notebook and mobile phone, etc) to enjoy mobile services almost anytime and anywhere. However, open nature of networks demands for security concern of paid and protected resources available over the network [1–5]. Authentication mechanism becomes an essential need before a remote user can access the services. Since then Lamport [6] proposed the first authentication scheme, a number of authentication schemes have been put forward for different applications [7–13].
However, most of the existing password authentication schemes are based on a single-server environment which are unfit for the multi-server environments. Recently, a large number of smart cards based remote user authentication schemes for multi-server environments have been proposed. In addition, compared with other authentication schemes, schemes that only use random numbers and a hash function were getting much more attention because of their low computation costs. In 2008, Tsai [14] proposed an efficient multi-server authentication scheme using the random number and one-way hash function. After that, numerous authenticated key agreement schemes were presented for multi-server environments one after another [15–17]. In 2012, Li et al. [18] proposed a novel authenticated key exchange scheme for multi-server environments. Unfortunately, Xue et al.[19] showed that Li et al.’s scheme did not resist some types of known attacks, such as vulnerability to verifier stolen, off-line password guess, replay, denial of service and forgery attacks. Then, Xue et al. proposed an improved scheme to remedy the weaknesses of Li et al.’s scheme. Nevertheless, Lu et al.[20] observed that Xue et al.’s scheme was not only really insecure against masquerade and insider attacks but also was vulnerable to off-line password guessing attack. To improve the shortcomings of Xue et al.’s scheme, Lu et al. proposed a slight modified authentication scheme for multi-server environments.
All above mentioned authentication schemes are based on password and smart cards. Note that the password cannot be considered as a unique identity identifier and it’s needed to be remembered. Moreover, possibility of password guessing attack is also a concern. Compared with cryptographic keys and passwords, biometric keys (e.g.fingerprint, face, iris, hand geometry and palm-print, etc.) have many advantages [21], for example, they are difficult to lose or forget; they are difficult to copy or share; they are difficult to forge or distribute biometrics; they are difficult to guess; they are more difficult to break biometric keys. Recently, Chuang et al.[22] presented an efficient biometrics based authentication scheme using smart cards for multi-server environments, which was previously considered to be have more security properties. However, Mishra et al. [23] showed that Chuang et al.’s scheme was vulnerable to stolen smart card attack, server spoofing attack and impersonation attack. In addition, they proposed an improved biometrics-based multi-server authenticated key agreement scheme using smart cards and they claimed that their scheme satisfied all desirable security requirements. Unfortunately, this paper will demonstrate that the scheme cannot really resist replay attack and cannot provide an efficient password change phase.
In this paper, we concentrate on the security weaknesses of the three-factor authentication scheme by Mishra et al. After carefully analysis, we find their scheme does not really resist replay attack while fails to provide an efficient password change phase. We further propose an improvement of Mishra et al.’s scheme with the purpose of preventing the security threats of their scheme. We demonstrate the proposed scheme is given to strong authentication against several attacks including attacks showed in the original scheme. In addition, we compare the performance and functionality with other related schemes.
The rest of paper is organized as follows: In Section 2 and Section 3, we review and analyze the Mishra et al.’s scheme. In Section 4, we propose an enhancement authentication scheme for multi-sever environments. In Section 5, we present a security analysis of our scheme. Section 6 shows security and performance analyses by comparing our scheme with previous schemes. We conclude in Section 7.
Review of Mishra et al.’s scheme
There are three phases relating to Mishra et al.’s scheme which consists of the registration, login and authentication and password updating. Table 1 lists the notations used in this paper.
Registration
Suppose RC is the trusted third party responsible for registration of Ui and Sj.
Server registration.
- Sj sends the registration request to RC;
- After receiving the request, RC sends the key PSK to Sj through a secure channel;
- Upon receiving the secret key PSK, Sj stores it with aim to authorize a legitimate user.
User registration.
- Ui selects his identity IDi, password PWi and keys his biometrics BIOi. Then, Ui generates a random number Ni, computes W1 = h(PWi∣∣Ni), W2 = h(IDi⊕Ni) and sends the registration message {IDi, W1, W2} to RC via a secure channel.
- RC computes Ai = h(IDi∣∣x∣∣Tr), Bi = h(Ai), Xi = Wi⊕Bi, Yi = h(PSK)⊕W2 and Zi = PSK⊕Ai, where Tr is the registration time. Then, RC issues the smart card SCi to Ui which contains {Xi, Yi, Zi, h(⋅)} over a secure channel.
- Upon receiving SCi, Ui enters his personal biometric BIOi at the sensor and computes N = Ni⊕H(BIOi), V = h(IDi∣∣Ni∣∣PWi). Finally, Ui stores {Xi, Yi, Zi, N, V, h(⋅)} into SCi.
Login and authentication
- Ui inserts SCi into the terminal and inputs his identity IDi, password PWi and imprints his biometrics BIOi at the sensor.
- SCi computes Ni = N⊕h(BIOi) and checks . If it holds, SCi continues to compute W1 = h(PWi∣∣Ni), W2 = h(IDi⊕Ni), Bi = Xi⊕Wi and h(PSK) = Yi⊕W2. Then, SCi generates a random number n1 and computes M1 = h(PSK)⊕n1, M2 = IDi⊕h(n1∣∣Bi) and M3 = h(IDi∣∣n1∣∣Bi). Finally, Ui sends {Zi, M1, M2, M3} to Sj.
- When receiving the message from SCi, Sj immediately computes Ai = Zi⊕PSK, n1 = M1⊕h(PSK), IDi = M2⊕h(n1∣∣h(Ai)) and checks whether . If it is equal, Sj generates a random number n2 and computes SKji = h(IDi∣∣SIDj∣∣Bi∣∣n1∣∣n2), M4 = n2⊕h(IDi∣∣n1), M5 = h(SKji∣∣n1∣∣n2). Then, Sj sends {SIDj, M4, M5} to SCi.
- SCi first computes n2 = M4⊕h(IDi∣∣n1), SKij = h(IDi∣∣SIDj∣∣Bi∣∣n1∣∣n2) and then checks whether h(SKij∣∣n1∣∣n2) is consistent with M5. If it is true, SCi computes M6 = h(SKij∣∣n1∣∣n2) and delivers it to Sj.
- Sj verifies the verification condition . If this verification holds, Sj can now use the keys SKji to communicate with Ui securely.
Security analysis of Mishra et al.’s scheme
This section presents a cryptanalysis of a recently scheme proposed by Mishra et al. We show their scheme does not satisfy the key security attribute such as vulnerability to replay attack and incorrect password change phase. We assume that a malicious adversary 𝓐 has totally supervised the communication channel in login and session key establishment phases. In other words, 𝓐 has the capacity to intercept, insert, delete, refresh or update any information delivered between Ui and Sj [6].
Not withstanding the replay attack
Suppose an adversary 𝓐 has intercepted a past login message {Zi, M1, M2, M3}. He is able to launch a replay attack and login to the server by resending the eavesdropped message {Zi, M1, M2, M3} to Sj. In other words, the adversary without running the “Login phase”, sends the eavesdropped message {Zi, M1, M2, M3} to Sj. In the “Login and authentication”, upon receiving the message {Zi, M1, M2, M3}, Sj computes Ai = Zi⊕PSK, n1 = M1⊕h(PSK), IDi = M2⊕h(n1∣∣h(Ai)), and checks whether is equal to the received M3 or not. Since M3 and are equal, Sj will authenticate 𝓐 and 𝓐 will be able to login to Sj. Thus, 𝓐 can easily login to Sj by re-sending an old login message. Since Sj does not check the freshness of the received login message {Zi, M1, M2, M3} and authenticate Ui in (3) of the “Login and authentication”, Sj will not be able to discover replay attack.
Incorrect password change phase
The user Ui inserts his smart card into a card reader and enters his identity IDi, password PWi and imprints his personal biometric BIOi at the sensor corresponding to his smart card. Then smart card computes Ni = N⊕h(BIOi), and compares with the stored value of V in its memory to verify the legitimacy of Ui. Once the authenticity of cardholder is verified then Ui can instruct smart card to change his password. Afterwards, smart card asks the cardholder to resubmit a new password , then Xi = Bi⊕h(PWi∣∣Ni) and V = h(IDi∣∣Ni∣∣PWi) stored in the smart card can be updated with and , where . The value contains older password PWi in h(PWi∣∣Ni). Therefore, the modified is not correct.
The proposed scheme
In this section, we will present our robust biometrics based authentication scheme using smart cards for multi-sever environments. In our scheme, there are also three participants, the user Ui, the server Sj and the registration center RC. RC chooses the secret key PSK and a secret number x and shares them with Sj via a secure channel. We will describe all the phases relating to our scheme in the subsections, i.e. registration, login and authentication, and password update, where registration and login and authentication phases are shown in Fig 1.
Registration
- Ui keys his biometrics BIOi, identity IDi and password PWi. Then, Ui sends {IDi, h(PWi∣∣H(BIOi))} to RC.
- Upon receiving the message from Ui, RC computes Xi = h(IDi∣∣x), V = h(IDi∣∣h(PWi∣∣H(BIOi))). Then, RC stores {Xi, Vi, h(PSK)} into a smart card and submits them to Ui.
- Ui computes Yi = h(PSK)⊕y, and replaces h(PSK) with Yi. Finally, the smart card stores the values of {Xi, Yi, Vi, h(⋅)}.
Login and authentication
- Ui inserts his smart card into device and enters his identity IDi, password PWi and biometrics BIOi. Then, the smart card validates whether Vi = h(IDi∣∣h(PWi∣∣H(BIOi))) is equal to the stored V. If it holds, the smart card generates a random number n1 and computes K = h((y⊕Yi)∣∣SIDj), M1 = K⊕IDi, M2 = n1⊕K, M3 = h(PWi∣∣H(BIOi))⊕K, Zi = h(Bi∣∣n1∣∣h(PWi∣∣H(BIOi))∣∣T1). Finally, Ui submits {Zi, M1, M2, M3, T1} to Sj, where T1 is the current timestamp.
- Upon receiving the message from Ui, Sj first checks whether Tc−T1 ≤ ΔT and then computes K = h(SIDj∣∣h(PSK)) by using a secure pre-shared key PSK. Then, Sj retrieves IDi = M1⊕K, n1 = M2⊕K, h(PWi∣∣BIOi) = M3⊕K. Now, Sj computes Xi = h(IDi∣∣x) and verifies whether . If it holds, Sj generates a random number n2 and computes SKji = h(n1∣∣n2∣∣K∣∣Xi), M4 = n2⊕h(n1∣∣h(PWi∣∣H(BIOi))∣∣Xi), M5 = h(IDi∣∣n1∣∣n2∣∣K∣∣T2). Then, Sj sends back authentication message {M4, M5, T2} to Ui, where T2 is the current timestamp.
- After checking the freshness of T2, Ui first computes n2 = M4⊕h(n1∣∣h(PWi∣∣H(BIOi))∣∣Xi) and then verifies whether h(IDi∣∣n1∣∣n2∣∣K) is equal to the received M5. If they are equal, Ui computes the common session key SKij = h(n1∣∣n2∣∣K∣∣Xi) and sends {M6 = h(SKij∣∣IDi∣∣n2∣∣T3), T3} to Sj, where T3 is the current timestamp.
- Sj verifies the freshness T3 and the correctness of M6 by using SKji. If they do not hold, Sj stops the execution; Otherwise, Sj confirms the common session key SKji with Ui.
Password updating
Ui first inputs his smart card into the device and provides his identity IDi, password PWi and biometrics BIOi. Then, the smart card validates whether Vi = h(IDi∣∣h(PWi∣∣H(BIOi))) is equal to the stored Vi. If they are not equal, the smart card refuses the request; Otherwise, Ui keys in the new password . Finally, the smart card computes and replaces Vi by .
Security analysis of the proposed scheme
In this section, we first adopt Burrows-Abadi-Needham (BAN)Logic [24] to demonstrate the completeness of the proposed scheme. Then, we conduct discussion and a cryptanalysis of the proposed scheme through both the informal and formal analyses.
Verifying the proposed scheme with BAN logic
BAN logic [24] is a set of rules for defining and analyzing information exchange schemes. It helps its users determine whether exchanged information is trustworthy, secured against eavesdropping, or both. It has been highly successful in analyzing the security of authentication schemes. First, we introduce some notations and logical postulates of BAN logic in Table 2.
- BAN logical postulates
- Message-meaning rule: : if A believes that the key K is shared by A and B, and sees X encrypted with K, then A believes that B once said X.
- Fresh conjuncatenation rule: : if A believes freshness of X, then A believes freshness of the (X, Y).
- Belief rule: : if A believes X and Y, then A believes (X, Y).
- Nonce-verification rule: : if A believes that X could have been uttered only recently and that B once said X, then A believes that B believes X.
- Jurisdiction rule: : if A believes that B has jurisdiction over X and A trusts B on the truth of X, then A believes X.
- Establishment of security goals
- Idealized scheme
Sj: < n1, Xi, h(PWi∣∣H(BIOi)) > n2, (IDi, n1, n2, T2)K - Initiative premises
p1. Ui∣ ≡ #n1 p2. Ui∣ ≡ Sj ⇒ #n2 p3. Sj∣ ≡ #n1 p4. Sj∣ ≡ #n2
p7. Ui∣ ≡ IDi p8. Sj∣ ≡ Ui ⇒ h(PWi∣∣BIOi)
p9. Sj∣ ≡ Ui ⇒ IDi p10. Ui∣ ≡ Sj ⇒ Xi
p11. . - Scheme analysis
a1. By p5 and Sj⊲ < n1, IDi, h(PWi∣∣BIOi) > K, we apply the message-meaning rule to derive: Sj∣ ≡ Ui∣ ∼ (n1, IDi, h(PWi∣∣H(BIOi)))
a2. By a1 and p3, we apply the fresh conjuncatenation rule and the nonce-verification rule to derive: Sj∣ ≡ Ui∣ ≡ (n1, IDi, h(PWi∣∣H(BIOi)))
a3. By a2, p3 and p8, we apply the belief rule and the jurisdiction rule to derive: Sj∣ ≡ IDi
a4. By a3 and , we apply the message-meaning rule to derive:
a5. By p4 and a4, we apply the fresh conjuncatennation rule and the nonce-verification rule to derive:
g1. By a5, we apply the belief rule to derive:
g2. By g1 and p11, we apply the jurisdiction rule to derive:
a6. By p6 and Ui⊲(IDi, n1, n2, T2)K, we apply the message-meaning rule to derive: Ui∣ ≡ Sj∣ ∼ (IDi, n1, n2, T2)
a7. By p2 and a9, we apply the fresh conjuncatenation rule and the nonce-verification rule to derive: Ui∣ ≡ Sj∣ ≡ (IDi, n1, n2, T2)
a8. By a7, we apply the belief rule to derive: Ui∣ ≡ Sj∣ ≡ n2
a9. By p2 and a8, we apply the jurisdiction rule to derive: Ui∣ ≡ n2
a10. By a9 and Ui⊲ < n1, Xi, h(PWi∣∣BIOi) > n2, we apply the message-meaning rule to derive: Ui∣ ≡ Sj∣ ∼ (n1, Xi, h(PWi∣∣BIOi))
a11. By a10 and p1, we apply the fresh conjuncatennation rule and the nonce-verification rule to derive: Ui∣ ≡ Sj∣ ≡ (n1, Xi, h(PWi∣∣BIOi))
g3. By p1, p3, p4, p6, a11 and SKji = h(n1∣∣n2∣∣K∣∣Xi), we apply the fresh conjuncatennation rule and the nonce-verification rule to derive:
g4. By g3 and p12, we apply the jurisdiction rule to derive:
Informal security analysis
This subsection verifies whether the proposed scheme is secure against various kinds of known attacks. We assume that a malicious adversary 𝓐 has totally supervised the communication channel in login and session key establishment phases. In other words, 𝓐 has the capacity to intercept, insert, delete, refresh or update any information delivered between Ui and Sj [6].
Anonymity.
Ui’s identity IDi is well protected by the shared secret parameter K as a substitute for real ones, 𝓐 can not get users’ real identities. In addition, the unauthorized server cannot get IDi without knowing K since K is protected by the secret key PSK only known by the authorized server and is not exposed in the open channel. Thus, our scheme provides user anonymity, which can prevent the leakage of private user identities to malicious attackers.
Mutual authentication.
In order to authenticate Ui, Sj has to verify validity of the evidence Zi = h(Xi∣∣n1∣∣h(PWi∣∣H(BIOi))). The evidence is computed with the common secret parameter K only known Ui and Sj. In other words, (n1, IDi, h(PWi∣∣H(BIOi))) are derived from the valid login message {Zi, M1, M2, M3, T1} through K, no one can counterfeit the evidence. In addition, to compute Xi, secret key x is needed but only known by Sj. Moreover, checking h(SKij∣∣IDi∣∣n2) to further assist Sj in authenticating Ui because the session key is only known by Ui and Sj. To authenticate Sj, Ui needs to verify whether . Because IDi and K are only known by Ui and Sj, no one can forge a valid {M4, M5, T2} without them. Hence, mutual authentication between Ui and Sj is achieved.
Resist stolen smart card attack.
Even if 𝓐 has gathered [25] the information {Xi, Yi, Vi, h(⋅)} stored in the smart card, 𝓐 cannot figure out the login request message {Zi, M1, M2, M3, T1} without the secret key y. Moreover, 𝓐 cannot get the identity IDi and PWi since they are protected by hash functions with the Ui’s biometrics BIOi. Hence, 𝓐 still cannot succeed if he steals the smart card.
Session key agreement.
We provide the session key SK = h(n1∣∣n2∣∣K∣∣Xi) to protect the message communication between Ui and Sj, where (n1, n2, K, Xi) are known to anybody but Ui and Sj. In addition, SK is different in each session, 𝓐 has obtained a known session key cannot be used to calculate the value of the next session key.
Resist replay attack.
Assume 𝓐 has intercepted all the communication message {Zi, M1, M2, M3, T1, M4, M5, T2, M6, T3,} and tried to replay them to Ui or Sj to obtain authentication. However, it is impossible to come true since all the authenticated messages imply the timesstamp which is also exposed in public channel. If 𝓐 resends the transmitted messages, the receiver will immediately detect the attack through the authenticated message. Hence, our scheme can withstand replay attack.
Resist stolen verifier and insider attacks.
In the registration phase, RC does not directly get the Ui’s password PWi and biometrics information BIOi. Hence, 𝓐 performs a stolen verifier attack or insider attack will be hard.
Resist off-line guessing attack.
In our proposed scheme, trying to launch an off-line passsword guessing attack with the information stored in the smart card and the eavesdropped messages is trying to solve the input from the given hash value. Since the identity IDi and the random number Ni are required with the purposed of knowing PWi, both the secrets are protected by the hash function and known by the user himself.
Formal security analysis of the proposed scheme
This subsection presents the formal security analysis of our scheme and shows that it is secure. For this, we first define the following hash function [26].
Definition 1. A secure one-way hash function h:{0, 1}* → {0, 1}n, which takes an input as an arbitrary length binary string x ∈ {0,1}* and outputs a binary string h(x) ∈ {0,1}n and satisfies the following requirements: a. Given y ∈ Y, it is computationally infeasible to find an x ∈ X such that y = h(x); b. Given x ∈ X, it is computationally infeasible to find another x′ ≠ x ∈ X, such that h(x′) = h(x); c. It is computationally infeasible to find a pair (x′, x) ∈ X′ × X, with x′ ≠ x, such that h(x′) = h(x).
Theorem 1. Under the assumption that the one-way hash function h(⋅) closely behaves like an oracle, then our scheme is provably secure against an attacker 𝓐 for protecting user’s personal information including identity IDi, password PWi and biometrics BIOi, sever’s private key x and PSK.
Proof. The formal security proof of our scheme is similar to that as in [27–28]. Using the following oracle to construct 𝓐 who will have the ability to derive the user’s IDi, password PWi, biometrics BIOi, sever’s private key x and PSK.
Reveal: This random oracle will unconditionally output the input x from the given hash value y = h(x).
𝓐 runs the experimental algorithm showed in Table 3, for our biometrics based authentication and key agreement scheme using smart cards for multi-server environments, say BAKASSCMSE.
Define the success probability for is and the advantage function for this experiment then becomes , where the maximum is taken over all 𝓐 with execution time t and the number of queries qR made to the Reveal oracle. Consider the experiment showed in Table 3 for 𝓐. If 𝓐 has the ability to solve the hash function problem provided in Definition 1, then he can directly derive Ui’s identity IDi, password PWi, biometrics BIOi, and Sj’s private key x and PSK. In this case, 𝓐 will discover the complete connections between Ui and Sj. However, it is a computationally infeasible problem to invert the input from a given hash value, i.e., , ∀ϵ > 0. Hence, we have , since depends on . As a result, there is no way for 𝓐 to discover the complete connections between Ui and Sj and our scheme is provably secure against an adversary for deriving (IDi, PWi, BIOi, x, PSK).
Performance and functionality analysis
In this section, we compare our scheme with other existing multi-server authenticated schemes ([18–20], [22–23]) regarding security and performance. Table 4 lists the functionality comparisons of our proposed scheme with other related schemes. It can be seen that the proposed scheme achieves all security and functionality requirements and is more secure than other related schemes.
For performance analysis, we compare the computational primitives involved in login and authentication phases of our scheme and other related schemes. To analyze the computational complexity of the schemes, we use hashing operation as the time complexity since XOR operations require very little computations. Fig 2 shows comparison regarding the performance. From this comparison, we can see that our proposed scheme has better efficiency in comparison with other schemes.
Conclusion and future work
In this paper, we presented a cryptanalysis of a recently proposed Mishra et al.’scheme and showed that their scheme was susceptible to replay attack while failed to provide an efficient password change phase. An improved scheme is proposed that inherits the merits of Mishra et al.’s scheme and resists different possible attacks. The proposed scheme is practical and efficient compared with other related schemes. Comprehensive security analysis proves that the robustness of our scheme is more secure than other related schemes. Among the open problems to be faced in the near future we can mention the study of specific applications and practical limitations of our scheme for mutual authentication using smart cards based on biometrics and their large-scale implementation in real multi-sever environments.
Author Contributions
Conceived and designed the experiments: YRL LXL XY YXY. Performed the experiments: YRL LXL XY YXY. Analyzed the data: YRL LXL XY YXY. Contributed reagents/materials/analysis tools: YRL LXL XY YXY. Wrote the paper: YRL LXL XY YXY.
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