Abstract
Strong designated verifier signature is a special digital signature in which a signature can only be verified by the designated verifier. As more and more mobile devices have been used in the scenarios of strong designated verifier signature, it raises a challenge to design a strong designated verifier signature scheme to meet security and efficiency simultaneously. Recently, Zhang et al. proposed a new strong designated verifier signature scheme with time limit to address the challenge. However, we show that their scheme is not secure against forgery attack and propose an improved strong designated verifier signature scheme using symmetrical encryption technology. Performance analysis shows that the proposed scheme can meet all security requirements and is more efficient than Zhang et al.’s strong designated verifier signature scheme.
Keywords
Introduction
As one of the pivotal technologies of information security, digital signature has been widely used in all kinds of applications to provide authentication, data integrality, and non-repudiation. In general, the validity of a signature can be checked by anyone who has the signer’s public key. In some case, the signature can be checked by its designated verifier only, such as electronic payment system and electronic voting system. To settle this question, Chaum and Van Antwerpen 1 introduced the concept of undeniable signature, in which the signer can completely control his or her signature by the participation of verifier under interaction protocol. However, their undeniable signature is vulnerable to blackmailing attack 2 and mafia attack. 3 Based on the similar concept, Jakobsson et al. 4 presented two new concepts about designated verifier signature (DVS) and strong DVS (SDVS). The DVS provides message authentication without non-repudiation. Only the designated verifier in DVS can check the validity of any signature that has designated to him or her. Because the designated verifier could simulate a signature that is distinguished from one that generated by the original signer, he or she could not transfer the conviction to others. In SDVS, the public key of designated verifier is involved to generate the signature and the secrete key of designated verifier is used to check the validity of message. Thus, SDVS achieves the goal of designated verification well. Saeednia et al. 5 proposed a formal definition of SDVS and an efficient specific SDVS scheme. From then on, many study results on the DVS/SDVS have been proposed. These proposed schemes are mainly be classified into three categories, public key cryptography (PKC)-based DVS,5–7 certificateless SDVS schemes8–11 and ID-based SDVS schemes.12–16
With the development of wireless communication technology, we have entered a wireless mobile Internet era. More and more mobile devices are used as the main tools for electronic payment, electronic voting, and so on. However, mobile devices are limited in computation capacity and energy, in which the complex cryptographic operations could not be executed perfectly and may face a dilemma in balancing efficiency and security. In addition, there may be a large number of messages should be checked and processed within time limit in the scenarios of SDVS. Therefore, it poses a new challenge on the design of SDVS scheme that should meet the requirement of security and efficiency for mobile devices.
Most recently, Zhang et al. 17 proposed an efficient secured SDVS scheme to meet the new requirements of SDVS. In Zhang et al.’s scheme, messages and timestamp are secretly embedded in signatures that could be recovered only by the signer and the designed verifier. Zhang et al. claimed that their scheme could resist the replay attack and forgery attack. However, a concrete example in section “Review and cryptanalysis of Zhang et al.’s scheme” demonstrates that their scheme is not secure against universal forgery attack.
To address the challenge of SDVS well, we propose an improved SDVS scheme over Zhang et al.’s 17 scheme in this article. In the proposed scheme, the message and timestamp could be transmitted in secret, where symmetric cryptography is involved to decrease computation cost without security loss. Security analysis shows that the proposed scheme can meet all security requirements of SDVS, and the comparison of computation cost shows that the proposed scheme needs less computation cost than Zhang et al.’s 17 scheme.
The rest of this article is organized as follows. Section “Preliminaries” reviews preliminaries about SDVS. Section “Review and cryptanalysis of Zhang et al.’s scheme” briefly reviews Zhang et al.’s 17 SDVS scheme and demonstrates their scheme’s deficiency. A new improved SDVS scheme using the symmetrical encryption technology is proposed in section “The proposed SDVS scheme.” Performance analysis is presented in section “Performance analysis” and conclusions in section “Conclusion.”
Preliminaries
In this section, we briefly introduce some knowledge about the bilinear pairing and the security model of the SDVS scheme. For simplicity, the main notations used in this article are listed in Table 1.
Notations and corresponding descriptions.
Bilinear pairing and computational problem
As listed in Table 1, e is the symmetric bilinear pairing, which satisfies the following properties:
Bilinearity:
Non-degeneracy: There exists
Computability: Given any two random points
Bilinear Diffie–Hellman (BDH) Problem:
18
Given three random points
Security model of the SDVS scheme
An SDVS scheme should meet the security requirements defined as follows.
1. Correctness
A secure SDVS scheme should ensure that each signature could be correctly verified in the polynomial time.
2. Non-transferability
Since the fact that the verifier can generate a transcript by the simulation algorithm, the third party has no ability to distinguish the signature from the transcript.
3. Strongness
The designated verifier must use his private key when he verifies the signature. This property ensures that the secret information in the signature would not be revealed.
4. Source hiding
Given the message, the signature, and all the private keys, the third party cannot also distinguish the signature’s generator.
5. Unforgeability
An adversary cannot forge a legal signature without knowing the participants’ private keys. The unforgeability of the SDVS scheme can be defined through a game played between a challenger
Setup: In this phase, the challenger
Queries: After obtaining system parameters,
Attack. Finally, the adversary
The DVS
Review and cryptanalysis of Zhang et al.’s scheme
In this section, we first review Zhang et al.’s 17 SDVS scheme. Then, we demonstrate that their scheme is vulnerable to forgery attack.
Review of the Zhang et al.’s scheme
There are five phases included in Zhang et al.’s SDVS scheme: setup phase, key-extract phase, signing phase, verifying phase, and simulation phase. For simple presentation, let Alice and Bob be the signer and the designated verifier in the scheme, respectively, in the rest of this article.
Setup phase. In this phase, private key generator (PKG) generates system parameters by the following steps.
PKG chooses two cyclic groups
PKG randomly selects a number
PKG chooses three hash functions:
Finally, PKG broadcasts system parameters
Key-extract phase. In this phase, PKG extracts user’s public/private key pairs. When a new registering user sends his identity
Signing phase. Assume Bob’s identifier is
Computes Bob’s public key
Selects time range T and computes timestamp
Computes
Finally, Alice sends the signature
Verifying phase. After receiving the signature
Simulation phase. After verifying the signature
Selects time range
Computes public key of Alice by
Computes
Finally, Bob saves the signature
Cryptanalysis of Zhang et al.’s scheme
Zhang claimed that their SDVS scheme could provide unforgeability. However, we demonstrate that a universal adversary
When
Because
After getting the secret value W,
When Bob receives the forged signature
The proposed SDVS scheme
In this section, an improved SDVS scheme over Zhang et al.’s scheme is proposed. The proposed scheme consists of five similar phases with Zhang et al.’s scheme.
Setup phase and key-extract phase. The two phases are same as Zhang et al.’s scheme. Therefore, we do not repeat here, and the details are available in section “Review and Cryptanalysis of Zhang et al.’s scheme.”
Signing phase. Given the message m, Alice performs the following steps to generate a DVS.
Computes Bob’s public key
Selects time range T and computes timestamp
Computes
Computes
Verifying phase. After receiving the signature
Computes
Computes m, r, and t by
Bob checks whether the equation
The details of signing phase and verifying phase in the proposed scheme is shown in Figure 1.
Simulation phase. After verifying the signature
Compute Alice’s public key
Select time range
Compute
Finally, Bob saves the signature

The signing phase and verifying phase of the proposed scheme.
Performance analysis
In this section, the security and the computational cost of the proposed SDVS scheme is evaluated first. Then, the proposed scheme is compared with Zhang et al.’s SDVS scheme in terms of security and computation cost.
Security analysis
Correctness
Because
Unforgeability
It is well known that the BDH problem is difficult. Next, we will show that the proposed scheme can resist the universal forge attack based on BDH problem as follows.
Lemma 1
If there exists an adversary
Proof
Assume that Alice’s public key is
Note that Bob needs to recover
However, it is a BDH problem to solve equation (1). Therefore, it contradicts to the assumption that
Non-Transferability
As shown in simulation phase of our proposed scheme, Bob generates a transcript
It is very difficult to distinguish
Source hiding
In the proposed scheme, two undistinguished valid signatures, that is,
Strongness
When the designated verifier Bob checks the signature
The comparison of security and computation cost
In this subsection, the proposed scheme is compared with Zhang et al.’s 17 scheme in terms of security and computation cost.
Let P1, P2, P3, P4, and P5 denotes correctness, unforgeability, non-transferability, source hiding, and strongness, respectively. The security comparisons of three SDVS schemes are shown in Table 2.
Security comparisons with similar schemes.
As a result of the security comparisons in Table 2, our proposed scheme can meet all important security requirements of SDVS schemes, such as correctness, unforgeability, non-transferability, source hiding, and strongness. However, Lee et al.’s scheme and Zhang et al.’s scheme cannot provide unforgeability. Therefore, the proposed scheme is secure than the other two schemes.
Next, we analyze the computation cost of the proposed scheme. Because the major computations of SDVS schemes are produced in signing phase and verifying phase, the computation costs of two phases will be analyzed. For convenience, let
In our proposed scheme, the computation costs of signing phase consist of one bilinear pairing operation, one operation of Map-to-Point hash function, two operations of one-way hash function, and one symmetric encryption operation, that is, the total is
Comparison of computation cost with similar schemes.
It is well known that the computation costs of a modular exponentiation operation
From the above analysis, it can be concluded that our proposed scheme not only provides better security prosperities but also is more efficient than Zhang et al.’s 17 scheme.
Conclusion
In this article, we demonstrate that Zhang et al.’s proposed SDVS scheme is not secure against forgery attack. To meet the requirement of security and efficiency for mobile devices in SDVS, we propose an improved SDVS scheme by using the symmetrical encryption technology. The security analysis shows that the proposed scheme can meet all security requirements, and the comparison of computation cost shows that the proposed scheme needs less computation cost than Zhang et al.’s scheme in both signing phase and verification phase. Therefore, the proposed scheme is more suitable for the scenarios of SDVS in wireless mobile Internet era.
Footnotes
Handling Editor: Carlos Moreno
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The work was supported in part by the National Natural Science Foundation of China under grant no. 61862052.
