Blind signature is the concept to ensure anonymity of e-coins. Untracebility and unlinkability are two main properties of real coins, which require mimicking electronically. Whenever a user is permitted to spend an e-coin, he is in need to fulfill above requirements of blind signature. This paper proposes a proxy blind signature scheme with which a proxy is able to make proxy blind signature wh...

A convertible authenticated encryption scheme simultaneously provides the functions of integration, authentication, confidentiality, and non-repudiation. In this paper, we first separately point out that any adversary can forge a converted signature in Araki’s scheme and MaChen’s scheme. Moreover, we further improve the weakness in WuHsu’s scheme, which is to convert the signature into an ordin...

Han et al. proposed the first identity-based undeniable signature scheme at the fourth ACM conference on electronic commerce. Zhang et al. showed two attacks (the denial attack and the forge attack) against the scheme. In this paper, we modify the scheme to make it secure against these attacks. We also show how to modify our scheme to make it be an ID-based convertible undeniable signature scheme.

In this paper, we present a universal forgery attack on Kang et al.’s identity-based strong designated verifier signature (IBSDVS) scheme. We show anyone can forge a valid IBSDVS on an arbitrary message without the knowledge of the private key of either the signer or the designated verifier. Moreover, we point out that Kang et al.’s scheme does not satisfy the properties of strongness and nonde...

Authentication of individuals is rapidly becoming an important issue. On-line signature verification is one of the methods that use biometric features. This paper proposes a new HMM algorithm is for on-line signature verification. After preprocessing, input signature is discretized in a polar coordinate system. This particular discretization leads to a simple procedure for assigning initial sta...

Redactable signature schemes allow to black out predefined parts of a signed message without affecting the validity of the signature, and are therefore an important building block in privacy-enhancing cryptography. However, a second look shows, that for many practical applications, they cannot be used in their vanilla form. On the one hand, already the identity of the signer may often reveal se...

This thesis is divided into two distinct parts. The first part of the thesis explores various deniable signature schemes and their applications. Such schemes do not bind a unique public key to a message, but rather specify a set of entities that could have created the signature, so each entity involved in the signature can deny having generated it. The main deniable signature schemes we examine...

Convertible authenticated encryption (CAE) schemes enable the signer to send a confidential message and its corresponding signature to the designated recipient. The recipient can also convert the signature into a conventional one which can be verified by anyone. Integrating the properties of self-certified public key systems, this paper presents efficient and computationally indistinguishable s...

In this article, we shall adopt the concepts of elliptic curve cryptosystems and self-certified public keys to build a novel digital signature scheme with message recovery. The public key and the identity of the user can be authenticated simultaneously in recovering the message. In addition, we shall also present three extended digital signature schemes based on the proposed scheme. The first i...