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Identity‐based encryption (IBE), introduced by Shamir, eliminates the need for public‐key infrastructure. The sender can simply encrypt a message by using the recipient's identity (such as email or IP address) without needing to look up the public key. In particular, when ciphertexts of an IBE do not reveal recipient's identity, this scheme is known as an anonymous IBE scheme. Recently, Blazy et al. (ARES '19) analysed the trade‐off between public safety and unconditional privacy in anonymous IBE and introduced a new notion that incorporates traceability into anonymous IBE, called anonymous IBE with traceable identities (AIBET). However, their construction is based on the discrete logarithm assumption, which is insecure in the quantum era. In this paper, we first formalize the consistency of tracing key of the AIBET scheme to ensure that a ciphertext cannot be traced with the use of wrong tracing keys. Subsequently, we present a generic formulation concept that can be used to transform structure‐specific lattice‐based anonymous IBE schemes into an AIBET. Finally, we apply this concept to Katsumata and Yamada's compact anonymous IBE scheme (Asiacrypt '16) to obtain the first quantum‐resistant AIBET scheme that is adaptively secure under the ring learning with errors assumption without random oracle. [ABSTRACT FROM AUTHOR]

Without revealing data in the plain, public key encryption with equality test can achieve the basic cryptographic functionalities required. However, the extended version, i.e., public encryption with filtered equality test (PKE-FET) can be used to only test the ciphertext only for some data. In this paper, we revisit the notion of PKE-FET on various security models. We provide a formal definition for the security of PKE-FET and present a new scheme to achieve a stronger level of security than the existing scheme. [ABSTRACT FROM AUTHOR]

Visual cryptography (VC) is a variant form of secret sharing. In general threshold setting, the k -out-of- n VC allows that, in a set of n participants, any k can recover and reconstruct the secret by stacking their shares. Recently, the notion of multiple-secret VC has been introduced to embed multiple secrets. Region incrementing visual cryptography (RIVC) is referred to as a new type of multi-secret VC. RIVC defines s layers and takes and L_{2},L_{3} in two-out-of-three RIVC, where any two participants in L_{2} can recover S2 and three in L3 can recover S2,S3 . However, there is another multi-secret VC, called fully incrementing visual cryptography (FIVC), which also has the layers, but only one secret Si will reveal in one layer Li . In this paper, our stating point is to propose a new notion of non-monotonic visual cryptography (NVC) for human vision system as a primitive to construct FIVC. We first present an ideal construction of simple NVC, which relies on a slightly unreasonable assumption. Based on the simple NVC, we show a few methods to extend the functionality for complicated cases of NVC. Then, the generic construction is presented as a systematic manner to eliminate the above-mentioned assumption. Finally, we formally introduce a transformation NVC-to-FIVC algorithm, which takes NVC as input and then produce a construction of FIVC. Also, show a demonstration the NVC-to-RIVC algorithm, and analyze some properties regarding NVC. We believe that the notion of NVC can potentially find other applications and is of independent interest. [ABSTRACT FROM PUBLISHER]

In cryptography, security models play important roles to define the security with potential attacks. Following the security models, a scheme is analysed to be secure or insecure against those considered attacks. However, certificateless signatures (CLSs) are well-known notions to solve the key escrow problem of identity-based signatures, but the adversaries’ attack power is not well defined. In typical CLS setting, the full private key is composed of two parts that are respectively generated by two different parties, and therefore, the security models will be more complicate than other systems. In general, there are two types of adversaries in CLS, and further can be extended into many security levels due to attack power. In this paper, a comprehensive study focuses on the security models of CLSs. We not only consider two security issues, public key replacement, and strong unforgeability, but also revisit all feasible and potential adversaries’ abilities. According to the research results, we show the generalization of security models which consists of all cases of the adversaries. Finally, we give a security comparison with literature works. [ABSTRACT FROM PUBLISHER]

User identification plays an important role for access control in networks. Recently, Hsu and Chuang proposed a user identification scheme for distributed computer networks, which can also provide key agreement and user anonymity. However, Tsai pointed out the weakness of Hsu-Chuang's scheme and proposed an improved scheme. In this paper, we present two attacks to examine that some user identification schemes have a serious security loophole. Finally, we propose a new user identification scheme, which is more secure than the existing schemes. [ABSTRACT FROM AUTHOR]

Visual secret sharing (VSS) is a noteworthy variant of secret sharing. One special property of VSS is that the security of VSS is achieved by loosing the contrast and the resolution of the secret image. Generally, the reconstructed secrets of these schemes are considered to be visible if and only if the contrast is greater than 0. However, VSS is based on the human vision system (HVS), thus the visibility is not only dependent on the contract. In this paper, we discuss the limit of human vision for VSS (LHV-VSS), because HVS is actually complicated. We take several human vision parameters into consideration, and propose a profile to analyze the upper bound of n for k-out-of- n VSS schemes based on the just noticeable difference (JND) profile. We conclude some cases of VSS schemes are invisible practically according to the analyses. Finally, we give a definition for VSS, visibility condition. [ABSTRACT FROM AUTHOR]

In this study, the authors consider certificateless signature (CLS) schemes for strong non‐repudiation. They show that previous security models which ensure that any user can have a unique key pair cannot guarantee a CLS scheme to achieve strong non‐repudiation. The authors then fix the security model and propose a new CLS scheme which provides strong non‐repudiation under the new model, assuming the computational Diffie–Hellman problem is intractable. [ABSTRACT FROM AUTHOR]

Visual cryptography (VC), proposed by Naor and Shamir, has numerous applications, including visual authentication and identification, steganography, and image encryption. In 2006, Horng showed that cheating is possible in VC, where some participants can deceive the remaining participants by forged transparencies. Since then, designing cheating-prevention visual secret-sharing (CPVSS) schemes has been studied by many researchers. In this paper, we cryptanalyze the Hu–Tzeng CPVSS scheme and show that it is not cheating immune. We also outline an improvement that helps to overcome the problem. [ABSTRACT FROM PUBLISHER]