Unforgeability and blindness are two important properties of blind signature. The latter means that after interacting with various users, the signer is unable to link a valid message-signature pair. In ICCSA 2006, Zhang et al. showed that a signer in an identity-based blind signature scheme proposed by Huang et al. is able to link a valid messagesignature pair obtained by some user. They also p...

A (t,n) threashold proxy signature scheme enables an original signer to delegate his/her signing power to n proxy signers such that any t or more proxy signers can sign messages on behalf of the original signer, but t-1 or less of them cannot produce a valid proxy signature. Based on the RSA cryptosystem, Hong proposed an efficient (t,n) threshold proxy signature for mobile agents. Cai et al. f...

In this paper, we propose a new multivariate signature scheme named MI-T-HFE as a competitor of QUARTZ. The core map of MI-T-HFE is of an HFEv type but more importantly has a specially designed trapdoor. This special trapdoor makes MI-T-HFE have several attractive advantages over QUARTZ. First of all, the core map and the public map of MI-T-HFE are both surjective. This surjectivity property is...

Group signature schemes allow a group member to anonymously sign on group’s behalf. Moreover, in case of anonymity misuse, a group authority can recover the issuer of a signature. This paper analyzes the security of two group signature schemes recently proposed by Tseng and Jan. We show that both schemes are universally forgeable, that is, anyone (not necessarily a group member) is able to prod...

Key substitution vulnerable signature schemes are signature schemes that permit an intruder, given a public verification key and a signed message, to compute a pair of signature and verification keys such that the message appears to be signed with the new signature key. Schemes vulnerable to this attack thus permit an active intruder to claim to be the issuer of a signed message. A digital sign...

Key substitution vulnerable signature schemes are signature schemes that permit an intruder, given a public verification key and a signed message, to compute a pair of signature and verification keys such that the message appears to be signed with the new signature key. Schemes vulnerable to this attack thus permit an active intruder to claim to be the issuer of a signed message. A digital sign...

Undeniable signature is an intriguing concept introduced by Chaum and Antwerpen at Crypto’89. In 1999, Lee and Hwang presented two group-oriented undeniable signature schemes with a trusted center. Their schemes are natural generalizations of Chaum’s zero-knowledge undeniable signature scheme proposed in 1990. However, we find that the Lee-Hwang schemes are insecure. In this paper, we demonstra...

Delegation of rights is a common practice in the real world. We present two identitybased threshold proxy signature schemes, which allow an original signer to delegate her signing capability to a group of n proxy signers, and it requires a consensus of t or more proxy signers in order to generate a valid signature. In addition to identity-based scheme, privacy protection for proxy singers and s...

A group signature scheme allows a group member of a given group to sign messages on behalf of the group in an anonymous and unlinkable fashion. In case of a dispute, however, a designated group manager can reveal the signer of a valid group signature. Based on the Camenisch-Michels group signature scheme [7, 8], Kim, Lim and Lee proposed the first group signature scheme with a member deletion p...