This article provides a mutual non-repudiation exchange protocol based on semi-trusted center and, the center dynamically produces time-marking, identifies the sender.

A directed threshold signature scheme without a trusted party;

Two forgery attacks and their corresponding conspiracy attacks are proposed against the(t,n) threshold signature scheme without a trusted party worked out by Wang Bin and Li Jian-hua(the WL Scheme for short).

A digital watermarking for relational databases algorithm which was based on secret sharing with a trusted party was proposed.

In order to meet the requirements of digital signature for messages with different importance,a secret sharing-multisignature scheme without a trusted center is proposed based on the techniques of joint random secret sharing and multisignature.

In this paper,a new secret-sharing multi-signature scheme without trusted center is analyzed,and a forged attack is given.

In this scheme,when an original signer finds that a proxy signer is malicious,he can revoke the malicious proxy signer s signing capability efficiently through a trusted authority.

New identity based Chameleon threshold signature without trusted dealer;

Usually there is no such an authority which can be trusted by everyone,so the scheme is more attractive than the ones with a trusted dealer.

In this paper, we propose a new (t, n) threshold signature scheme without trusted center based on discrete logarithm.

This paper proposes a threshold authentication scheme without trusted center’s participation.