Transformation from e-voting to e-cheque.

Although e-voting scheme and e-cheque scheme are two different applications, they have similarities in the scheme definitions and security properties. This inspires us to establish a relationship between the two schemes by formalising a generic transformation from e-voting to e-cheque scheme. Firstly, we define the scheme definitions and security models for both e-voting scheme and e-cheque scheme. Subsequently, we demonstrate a generic transformation framework from e-voting to e-cheque with asymptotic complexity of [Formula: see text] and design a formal proof to show that a secure e-voting scheme can be transformed into a secure e-cheque scheme. As a proof of concept, we apply our newly proposed transformation technique to the e-voting scheme proposed by Li et al. and obtain a concrete e-cheque scheme.

Twin-Schnorr: a security upgrade for the Schnorr identity-based identification scheme.

Most identity-based identification (IBI) schemes proposed in recent literature are built using pairing operations. This decreases efficiency due to the high operation costs of pairings. Furthermore, most of these IBI schemes are proven to be secure against impersonation under active and concurrent attacks using interactive assumptions such as the one-more RSA inversion assumption or the one-more discrete logarithm assumption, translating to weaker security guarantees due to the interactive nature of these assumptions. The Schnorr-IBI scheme was first proposed through the Kurosawa-Heng transformation from the Schnorr signature. It remains one of the fastest yet most secure IBI schemes under impersonation against passive attacks due to its pairing-free design. However, when required to be secure against impersonators under active and concurrent attacks, it deteriorates greatly in terms of efficiency due to the protocol having to be repeated multiple times. In this paper, we upgrade the Schnorr-IBI scheme to be secure against impersonation under active and concurrent attacks using only the classical discrete logarithm assumption. This translates to a higher degree of security guarantee with only some minor increments in operational costs. Furthermore, because the scheme operates without pairings, it still retains its efficiency and superiority when compared to other pairing-based IBI schemes.

Efficient and provable secure pairing-free security-mediated identity-based identification schemes.

Security-mediated cryptography was first introduced by Boneh et al. in 2001. The main motivation behind security-mediated cryptography was the capability to allow instant revocation of a user's secret key by necessitating the cooperation of a security mediator in any given transaction. Subsequently in 2003, Boneh et al. showed how to convert a RSA-based security-mediated encryption scheme from a traditional public key setting to an identity-based one, where certificates would no longer be required. Following these two pioneering papers, other cryptographic primitives that utilize a security-mediated approach began to surface. However, the security-mediated identity-based identification scheme (SM-IBI) was not introduced until Chin et al. in 2013 with a scheme built on bilinear pairings. In this paper, we improve on the efficiency results for SM-IBI schemes by proposing two schemes that are pairing-free and are based on well-studied complexity assumptions: the RSA and discrete logarithm assumptions.