## CryptoDB

### Xiang Xie

#### Publications

Year
Venue
Title
2021
PKC
Threshold ECDSA signatures provide a higher level of security to a crypto wallet since it requires more than t parties out of n parties to sign a transaction. The state-of-the-art bandwidth efficient threshold ECDSA used the additive homomorphic Castagnos and Laguillaumie (CL) encryption based on an unknown order group G, together with a number of zero-knowledge proofs in G. In this paper, we propose compact zero-knowledge proofs for threshold ECDSA to lower the communication bandwidth, as well as the computation cost. The proposed zero-knowledge proofs include the discrete-logarithm relation in G and the well-formedness of a CL ciphertext. When applied to two-party ECDSA, we can lower the bandwidth of the key generation algorithm by 47%, and the running time for the key generation and signing algorithms are boosted by about 35% and 104% respectively. When applied to threshold ECDSA, our first scheme is more optimized for the key generation algorithm (about 70% lower bandwidth and 70% faster computation in key generation, at a cost of 20% larger bandwidth in signing), while our second scheme has an all-rounded performance improvement (about 60% lower bandwidth, 27% faster computation in key generation without additional cost in signing).
2021
ASIACRYPT
Threshold Signatures allow $n$ parties to share the ability of issuing digital signatures so that any coalition of size at least $t+1$ can sign, whereas groups of $t$ or less players cannot. The currently known class-group-based threshold ECDSA constructions are either inefficient (requiring parallel-repetition of the underlying zero knowledge proof with small challenge space) or requiring rather non-standard assumptions. In this paper, under \emph{standard assumptions} we present efficient threshold ECDSA protocols from encryption schemes based on class groups \emph{without parallel repeating the underlying zero knowledge proof}, yielding a significant efficiency improvement in the key generation over previous constructions (even those based on non-standard assumptions). Along the way we introduce a new notion of \emph{promise} $\Sigma$-protocol that satisfies only a weaker soundness called \emph{promise extractability}. An accepting \emph{promise} $\Sigma$-proof for statements related to class-group-based encryptions does not establish the truth of the statement but provides security guarantees (promise extractability) that are sufficient for our applications. We also show how to simulate homomorphic operations on a (possibly invalid) class-group-based encryption whose correctness has been proven via our \emph{promise} $\Sigma$-protocol. We believe that these techniques are of independent interest and applicable to other scenarios where efficient zero knowledge proofs for statements related to class-group is required.
2016
EUROCRYPT

#### Coauthors

Handong Cui (1)
Yi Deng (1)
Nicolas Gama (1)
Malika Izabachène (1)
Shunli Ma (1)
Phong Q. Nguyen (1)
Xuyang Song (1)
Hailong Wang (1)
Tsz Hon Yuen (1)
Xinxuan Zhang (1)