## CryptoDB

### Jianhua Li

#### Publications

Year
Venue
Title
2008
EPRINT
Recently, democratic group signatures(DGSs) particularly catch our attention due to their great flexibilities, \emph{i.e}., \emph{no group manager}, \emph{anonymity}, and \emph{individual traceability}. In existing DGS schemes, individual traceability says that any member in the group can reveal the actual signer's identity from a given signature. In this paper, we formally describe the definition of DGS, revisit its security notions by strengthening the requirement for the property of traceability, and present a concrete DGS construction with $(t, n)$-\emph{threshold traceability} which combines the concepts of group signatures and of threshold cryptography. The idea behind the $(t, n)$-threshold traceability is to distribute between $n$ group members the capability of tracing the actual signer such that any subset of not less than $t$ members can jointly reconstruct a secret and reveal the identity of the signer while preserving security even in the presence of an active adversary which can corrupt up to $t-1$ group members.
2007
EPRINT
Digital signature schemes based on public-key cryptosystems generally permit existential forgery, except the schemes are equipped with some message formatting mechanisms, such as using hash functions or padding redundancies. In 2004, Chang et al. proposed a new digital signature scheme, and claimed the scheme without using any hash function or padding any redundancy can resist forgery attacks. However, many attacks on Chang et al.'s scheme were presented. Kang et al. also gave an effective improvement to resist these forgery attacks. In this letter, we gave a further improvement to shorten the signed signature. Our improvement keeps the security of Kang et al.'s scheme and makes it more efficient in computation and communication.
2007
EPRINT
A password-based tripartite key agreement protocol is presented in this paper. The three entities involved in this protocol can negotiate a common session key via a shared password over insecure networks. Proofs are given to show that the proposed protocol is secure against forging and chosen message attacks in the case of without actually running a dictionary attack.
2007
EPRINT
Kallahalla et al. presented a RSA-based Forward Key Rotation mechanism in secure storage scheme PLUTUS to ensure that the key used for encrypting updated files is related to the keys for all files in the file group. The encryption scheme based on Forward Key Rotation is such a scheme that only the authorized person is allowed access to the designated files and the previous versions. In this paper, we present a Forward Key Rotation storage scheme based on discrete logarithm and prove its security under random oracle model. Moreover, we propose another improved Forward Key storage scheme from pairing on elliptic curves. Compared to the scheme presented by Kallahalla et al., our scheme uses relatively short keys to provide equivalent security. In addition, the re-generated keys can be verified to ensure that the keys are valid in the improved scheme.
2007
EPRINT
Recently, proxy re-encryption scheme received much attention. In this paper, we propose a proxy re-encryption used for divert ciphertext from one group to another. The scheme is bidirectional and any member can independently decrypt the ciphertexts encrypted to its group. We discuss the security of the proposed scheme and show that our scheme withstands chosen ciphertext attack in standard model.
2007
EPRINT
A group oriented encryption scheme is presented in this paper. In this scheme, a sender is allowed to encrypt a message using the group public key and send the ciphertext to the group. Any user in the group can independently decrypt the ciphertext via his private key. The scheme is secure against adaptively chosen ciphertext attack and collude attack.
2006
EPRINT
As a useful means of safeguarding privacy of communications, deniable authentication has received much attention. A Chameleon-based deniable authenticated key agreement protocol is presented in this paper. The protocol has following properties. Any one of the two participants canât present a digital proof to convince a third party that a claimed agreement has really taken place. Once a forgery occurs, the original entity can present a digital proof to disclose the forgery.
2006
EPRINT
In this paper we introduce a new approach of constructing time capsule signature. Our new construction captures the basic requirements defined by dodis \emph{et al.}, and it is also very straightforward and flexible. The time capsule signature provides an elegant way to produce a future signature" that becomes valid from a specific future time $t$, when a trusted third party (called \textit{Time Server}) publishes some trapdoor information associated with the time $t$. It also has many other advantages. Our work includes a developed security model of time capsule signature, a novel way of construction based on the bipartite ring signature, which is proven secure in the random oracle model and a concrete realization of the scheme.
2005
EPRINT
Certificateless public key cryptography was introduced to overcome the key escrow limitation of the identity-based cryptography. Most of the existing certificateless public key encryption schemes are based on Boneh and Franklin's identity-based encryption scheme (BF-IBE). In this paper, we construct a new certificateless public key encryption scheme from the efficient SK-IBE which has been proved to be IND-ID-CCA secure. The new scheme is more efficient on computation complexity or published public key information than the existing schemes.
2005
EPRINT
Certificateless public key cryptography was introduced to overcome the key escrow limitation of the identity-based cryptography. It combines the advantages of the identity-based cryptography and the traditional PKI. Recently, Dae Hyun Yum1 and Pil Joong Lee have proposed a generic series construction model of certificateless public key encryption (CL-PKE) which is built from generic primitives: identity-based encryption and public key encryption. However, this model pays much attention on the generic construction and neglects the nice properties of the bilinear pairings. In this paper, we propose an efficient CL-PKE scheme which is based on the nice algebraic properties of Weil pairing. The scheme works in a kind of parallel model and it is more efficient on computation or published public key information than the existing schemes.

#### Coauthors

Jun Ao (5)
Gongliang Chen (1)
Kefei Chen (1)
Xiangxue Li (1)
Jie Liu (1)
Chunbo Ma (5)
Changshe Ma (1)
Haifeng Qian (1)
Yijuan Shi (2)
Licheng Wang (1)
Miaomiao Zhang (1)
Dong Zheng (1)