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The telecare medicine information system enables the patients gain health monitoring at home and access medical services over internet or mobile networks. In recent years, the schemes based on cryptography have been proposed to address the security and privacy issues in the telecare medicine information systems. However, many schemes are insecure or they(More)
The telecare medical information system enables the patients gain health monitoring and access healthcare-related services over internet or mobile networks. Due to the open environment, the mutual authentication between the user and the telecare server will thus be in demand. Many smart card based authentication schemes for telecare medicine information(More)
In a proxy signature scheme, a potential signer delegates his signing power to a proxy, who signs a message on behalf of the original signer. In a blind signature scheme, the signee cannot link the relationship between the blind message and the signature of the chosen message. That is, the signee cannot make a linkage between the blind signature and the(More)
In this paper, we first show that a previous proxy signature scheme by delegation with certificate is not provably secure under adaptive-chosen message attacks and adaptive-chosen warrant attacks. The scheme does not provide the strong undeniability. Then we construct a proxy signature scheme by delegation with certificate based on Co-GDH group from(More)
A (t, n) threshold proxy signature scheme enables an original signer to delegate the signature authority to a proxy group of n member such that t or more than t proxy signers can cooperatively sign messages on behalf of the original signer. In the paper, we review the security of some nonre-pudiable threshold proxy signature schemes with known signers. We(More)
—Recently, Yang et al. proposed a three-party encrypted key exchange protocol (3PAKE) which is based on Elliptic curve cryptography. Their 3PAKE protocol is efficient because it requires less computation cost and less communication cost, which is well suitable for mobile commerce environments. However, Yang et al.'s 3PAKE protocol is susceptible to parallel(More)
Recently, Hsiang and Shih proposed a secure dynamic ID based remote user authentication scheme for multi-server environment. In this paper, we show that Hsiang and Shih's scheme is still vulnerable to off-line password guessing attacks, impersonation attacks and server spoofing attacks. And it cannot resist agai nst extracting secr et data by in tercepting(More)