## CryptoDB

### Dong Zheng

#### Publications

Year
Venue
Title
2015
EPRINT
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.
2008
EPRINT
To provide a high level of security guarantee cryptography is introduced into the design of the voting machine. The voting machine based on cryptography is vulnerable to attacks through covert channels. An adversary may inject malicious codes into the voting machine and make it leak vote information unnoticeably by exploiting the randomness used in encryptions and zero-knowledge proofs. In this paper a voting machine resistant to covert channels is designed. It has the following properties: Firstly, it is tamper-evident. The randomness used by the voting machine is generated by the election authority. The inconsistent use of the randomness can be detected by the voter from examining a destroyable verification code. Even if malicious codes are run in the voting machine attacks through subliminal channels are thwarted. Next, it is voter-verifiable. The voter has the ability to verify if the ballot cast by the machine is consistent with her intent without doing complicated cryptographic computation. Finally, the voting system is receipt-free. Vote-buying and coercion are prevented.
2007
EPRINT
This paper presents two fast digital signature schemes based on Diffie-Hellman assumptions. In the random oracle model, the first scheme S1 has a tight security reduction to the computational Diffie-Hellman (CDH) problem; and the second scheme S2 has a tight security reduction to the decisional Diffie-Hellman (DDH) problem. Comparing with existing signature schemes (whose security is tightly related to CDH problem) like EDL signature schemes, the signature generation of S1 is about 27% faster, and the verification is about 35% faster, if without considering the hash function evaluations. Comparing with existing signature schemes (whose security is tightly related to DDH problem) like KW-DDH signature scheme, the signing of S2 is about 40% faster and the verification is about 35% faster. The high efficiency of the proposed schemes is attributed to a new protocol EDL_mwz which implements the proof of equality of discrete logarithm. The EDL_mwz protocol outperforms its counterpart, the Chaum and Pedersen protocol, as its computation is about 38% faster and its bandwidth is |G| bits shorter. This new protocol may be of independent interests.
2007
EPRINT
Cryptography is an important tool in the design and implementation of electronic voting schemes for it provides the property of verifiability, which is not provided in the traditional voting. But in the real life, neither can most voters understand the profound theory of cryptographic e-voting nor can they perform the complicated cryptographic computation. An e-voting system is presented in this paper to leverage the use of cryptography between theory and practice. It combines the advantages of Moran-Naor's voting scheme and voting schemes based on homomorphic encryption. It makes use of cryptographic techniques, but it hides the details of cryptographic computation from voters. Voters can be convinced that the ballot is cast as intended. The tally can be verified in public. Compared with Moran-Naor's voting scheme, the new system has three advantages: the ballots can be recovered when the voting machine breaks down, the costly cut-and-choose zero-knowledge proofs for shuffling votes made by the voting machine are avoided and the partial tally result in each voting machine is kept secret.
2006
EPRINT
Temporal Key Integrity Protocol (TKIP) is a sub-protocol of IEEE 802.11i. TKIP remedies some security flaws in Wired Equivalent Privacy (WEP) Protocol. TKIP adds four new algorithms to WEP: a Message Integrity Code (MIC) called Michael, an Initialization Vector (IV) sequencing discipline, a key mixing function and a re-keying mechanism. The key mixing function, also called temporal key hash, de-correlates the IVs from weak keys. Some cryptographic properties of the S-box used in the key mixing function are investigated in this paper, such as regularity, avalanche effect, differ uniform and linear structure. V.Moen, H.Raddum and K.J.Hole point out that there exists a temporal key recovery attack in TKIP key mixing function. In this paper a method is proposed to defend against the attack, and the resulting effect on performance is also discussed.
2004
EPRINT
In 1988, Harn, Laih and Huang proposed a password authentication scheme based on quadratic residues. However, in 1995, Chang, Wu and Laih pointed out that if the parameters d b a , , and l are known by the intruder, this scheme can be broken. In this paper, we presented another attack on the Harn-Laih-Huang scheme. In our attack, it doesn’t need to know the parameters and it is more efficient than the Chang-Wu-Laih attack.

#### Coauthors

Xiaofeng Chen (1)
Ke-fei Chen (3)
Kefei Chen (2)
Xiaoli Dong (1)
Wei Han (3)
Tao Hao (1)
Xiangxue Li (2)
Jianhua Li (1)
Changshe Ma (2)
Xiaoyun Wang (1)
Jian Weng (1)
Lizhen Yang (1)
Qinglan Zhao (1)