Quantum e-commerce: A comparative study of possible protocols for online shopping and other tasks related to e-commerce

A set of quantum protocols for online shopping is proposed and analyzed to establish that it is possible to perform secure online shopping using different types of quantum resources. Specifically, a single photon based, a Bell state based and two 3-qubit entangled state based quantum online shopping schemes are proposed. The Bell state based scheme, being a completely orthogonal state based protocol, is fundamentally different from the earlier proposed schemes which were based on conjugate coding. One of the 3-qubit entangled state based scheme is build on the principle of entanglement swapping which enables us to accomplish the task without transmission of the message encoded qubits through the channel. Possible ways of generalizing the entangled state based schemes proposed here to the schemes which use multiqubit entangled states is also discussed. Further, all the proposed protocols are shown to be free from the limitations of the recently proposed protocol of Huang et al. (Quantum Inf. Process. 14, 2211-2225, 2015) which allows the buyer (Alice) to change her order at a later time (after initially placing the order and getting it authenticated by the controller). The proposed schemes are also compared with the existing schemes using qubit efficiency.Comment: It's shown that quantum e-commerce is not a difficult task, and it can be done in various way

Cryptanalysis of the Hwang-Shi Proxy Signature Scheme

[[abstract]]Recently, Hwang and Shi proposed an efficient proxy signature scheme without using one-way hash functions. In their scheme, an original signer needn't send a proxy certificate to a proxy signer through secure channels. However, there are two public key substitution methods that can be used to attack their scheme. In this article, we show that their scheme is vulnerable to the public key substitution attacks[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]EI[[booktype]]紙本[[booktype]]電子版[[countrycodes]]NL

[[alternative]]The Desing of Anonymous Proxy Automatic Signature Schemes for Distributed Compilers

計畫編號：NSC94-2213-E032-022研究期間：200508~200607研究經費：422,000[[abstract]]本計畫預定提出適用於分散式誠實製造編議器的匿名自動代理簽章 法，藉以抵抗(未知)電腦病毒的威脅。由於網際網路的普及，電腦病毒的 危害也變得比以往嚴重。雖然防毒軟體可以提供抵抗電腦病毒的保護，但 是防毒軟體無法偵測未知的電腦病毒。在另外一方面，數位簽章法可以偵 測未知的電腦病毒，因為數位簽章法驗證檔案是否被病毒更動過。利用誠 實製造編議器，日本學者Usuda 等人提出自動簽章法以抵抗電腦病毒，隨 後學者Lin 和Jan 提出他們的適用於分散式誠實製造編議器之自動簽章 法。不幸地Lin 和Jan 的方法不足以抵抗偽造簽章攻擊，另外存在原始程 式碼長度受限的限制。於是學者Hwang 和Li 提出他們的適用於分散式誠 實製造編議器之自動代理簽章法。 在Lin 和Jan 的方法與Hwang 和Li 的 方法中，代理編議器編議工作的伺服器之隱私並未受到保護。為了抵抗編 議器製造者偽造自動簽章攻擊，伺服器之公開金鑰與秘密金鑰並須分別用 於自動代理簽章的驗證與產生，然而維護伺服器之公開金鑰的變更過程是 十分不方便的事。若匿名自動代理簽章只需使用編議器製造者公開金鑰就 可以驗證，不僅可以保護伺服器之隱私，也可以方便匿名自動代理簽章法 的實用性。所以本計畫預定提出適用於分散式誠實製造編議器的匿名自動 代理簽章法。[[sponsorship]]行政院國家科學委員

Cryptanalysis of a threshold proxy signature with known signers

A scheme of threshold proxy signature with known signers was proposed by Hwang et al. In their scheme, the receiver can identify the proxy signers that actually generated a proxy signature. Tzeng et al. demonstrated that this signature scheme is insecure and proposed an improvement to mend the information leakage. This paper shows that the improved scheme is still insecure under the original signer¡¦s forgery attack

A publicly verifiable quantum signature scheme based on asymmetric quantum cryptography

In 2018, Shi et al. \u27s showed that Kaushik et al.\u27s quantum signature scheme is defective. It suffers from the forgery attack. They further proposed an improvement, trying to avoid the attack. However, after examining we found their improved quantum signature is deniable, because the verifier can impersonate the signer to sign a message. After that, when a dispute occurs, he can argue that the signature was not signed by him. It was from the signer. To overcome the drawback, in this paper, we raise an improvement to make it publicly verifiable and hence more suitable to be applied in real life. After cryptanalysis, we confirm that our improvement not only resist the forgery attack but also is undeniable

A survey on group signature schemes

Group Signature, extension of digital signature, allows members of a group to sign messages on behalf of the group, such that the resulting signature does not reveal the identity of the signer. Any client can verify the authenticity of the document by using the public key parameters of the group. In case of dispute, only a designated group manager, because of his special property, is able to open signatures, and thus reveal the signer’s identity. Its applications are widespread, especially in e-commerce such as e-cash, e-voting and e-auction. This thesis incorporates the detailed study of various group signature schemes, their cryptographic concepts and the main contributions in this field. We implemented a popular group signature scheme based upon elliptic curve cryptosystems. Moreover, the group signature is dynamic i.e. remains valid, if some members leave the group or some new members join the group. Full traceability feature is also included in the implemented scheme. For enhanced security the the scheme implements distributed roles of the group manager. We also analysed various security features, formal models, challenges and cryptanalysis of some significant contributions in this area

The Insecurity of Two Proxy Signcryption Schemes: Proxy Credential Forgery Attack and How to Prevent It

Securing different online e-business activities usually requires applying different cryptographic algorithms. The proxy signcryption algorithms are designed for applications such as online proxy auction or online proxy signatures on business contracts, which require a proxy agent to sign on confidential messages. This paper proposes a proxy credential forgery attack to two recent proxy signcryption schemes in the literature. Using the attack, a malicious proxy signer can create a fake proxy credential from his original credential to extend his signing power. Simple modifications to these two schemes are also provided in this paper to prevent the attack without adding too much computational complexity. In addition to the contribution of introducing a new type of attacks to signcryption schemes, the paper also points out that, while designing a secure proxy signcryption scheme, not only the unforgeability of proxy signatures is important, but also that of proxy credentials as well

Cryptanalysis and Performance Evaluation of Enhanced Threshold Proxy Signature Scheme Based on RSA for Known Signers

In these days there are plenty of signature schemes such as the threshold proxy signature scheme (Kumar and Verma 2010). The network is a shared medium so that the weakness security attacks such as eavesdropping, replay attack, and modification attack. Thus, we have to establish a common key for encrypting/decrypting our communications over an insecure network. In this scheme, a threshold proxy signature scheme based on RSA, any or more proxy signers can cooperatively generate a proxy signature while or fewer of them cannot do it. The threshold proxy signature scheme uses the RSA cryptosystem to generate the private and the public key of the signers (Rivest et al., 1978). Comparison is done on the basis of time complexity, space complexity, and communication overhead. We compare the performance of four schemes (Hwang et al. (2003), Kuo and Chen (2005), Yong-Jun et al. (2007), and Li et al. (2007), with the performance of a scheme that has been proposed earlier by the authors of this paper. In the proposed scheme, both the combiner and the secret share holder can verify the correctness of the information that they are receiving from each other. Therefore, the enhanced threshold proxy signature scheme is secure and efficient against notorious conspiracy attacks

Designated Verifier Threshold Proxy Signature Scheme without Random Oracles

In a $(t,n)$ designated verifier threshold proxy signature \, scheme, an original signer can delegate his/her signing power to $n$ proxy signers such that any $t$ or more out of $n$ proxy signers can sign messages on behalf of the original signer but $t-1$ or less of the proxy signers cannot generate a valid proxy signature. Of course, the signature is issued for a designated receiver and therefore only the designated receiver can validate the proxy signature. In this paper, we propose a new designated verifier threshold proxy signature scheme and also show that the proposed scheme has provable security in the standard model. The security of proposed scheme is based on the $GBDH$ assumption and the proposed scheme satisfies all the security requirements of threshold proxy signature schemes