## CryptoDB

### Baodian Wei

#### Publications

Year
Venue
Title
2015
EPRINT
2015
EPRINT
2015
EPRINT
2009
EPRINT
Chameleon signatures are based on well established hash-and-sign paradigm, where a \emph{chameleon hash function} is used to compute the cryptographic message digest. Chameleon signatures simultaneously provide the properties of non-repudiation and non-transferability for the signed message. However, the initial constructions of chameleon signatures suffer from the problem of key exposure: the signature forgery results in the signer recovering the recipient's trapdoor information, $i.e.,$ the private key. This creates a strong disincentive for the recipient to forge signatures, partially undermining the concept of non-transferability. Recently, some specific constructions of key-exposure free chameleon hashing are presented, based on RSA or pairings, using the idea of Customized Identities". In this paper, we propose the first key-exposure free chameleon hash scheme based on discrete logarithm systems, without using the gap Diffile-Hellman groups. Moreover, one distinguished advantage of the resulting chameleon signature scheme is that the property of message hiding" or message recovery" can be achieved freely by the signer. Another main contribution in this paper is that we propose the first identity-based chameleon hash scheme without key exposure, which gives a positive answer for the open problem introduced by Ateniese and de Mederious in 2004.
2008
EPRINT
On-line/Off-line signatures are used in a particular scenario where the signer must respond quickly once the message to be signed is presented. The idea is to split the signing procedure into two phases: the off-line and on-line phases. The signer can do some pre-computations in off-line phase before he sees the message to be signed. In most of these schemes, when signing a message $m$, a partial signature of $m$ is computed in the off-line phase. We call this part of signature the off-line signature token of message $m$. In some special applications, the off-line signature tokens might be exposed in the off-line phase. For example, some signers might want to transmit off-line signature tokens in the off-line phase in order to save the on-line transmission bandwidth. Another example is in the case of on-line/off-line threshold signature schemes, where off-line signature tokens are unavoidably exposed to all the players in the off-line phase. This paper discusses this exposure problem and introduces a new notion: divisible on-line/off-line signatures, in which exposure of off-line signature tokens in off-line phase is allowed. An efficient construction of this type of signatures is also proposed. Furthermore, we show an important application of divisible on-line/off-line signatures in the area of on-line/off-line threshold signatures.

#### Coauthors

Xiaofeng Chen (1)
Yusong Du (3)
Chong-zhi Gao (1)
Kwangjo Kim (1)
Chunming Tang (1)
Haibo Tian (1)
Dongqing Xie (1)
Huang Zhang (3)
Fangguo Zhang (4)