International Association for Cryptologic Research

International Association
for Cryptologic Research


Quan Yuan


Security of the Blockchain Against Long Delay Attack
The consensus protocol underlying Bitcoin (the blockchain) works remarkably well in practice. However proving its security in a formal setting has been an elusive goal. A recent analytical result by Pass, Seeman and shelat indicates that an idealized blockchain is indeed secure against attacks in an asynchronous network where messages are maliciously delayed by at most $$\varDelta \ll 1/np$$, with n being the number of miners and p the mining hardness. This paper improves upon the result by showing that if appropriate inconsistency tolerance is allowed the blockchain can withstand even more powerful external attacks in the honest miner setting. Specifically we prove that the blockchain is secure against long delay attacks with $$\varDelta \ge 1/np$$ in an asynchronous network.
Towards Security Two-part Authenticated Key Agreement Protocols
Songping Li Quan Yuan Jin Li
We first present a new security 2-AK protocol, which is more secure and more efficient than previously proposed ones. Meanwhile, we point that Xie's ID-2-AK protocol modified from McCullagh-Barreto in CT-RSA 2005 doesn't provide protection against KCI attack likewise, and finally utilize the modular arithmetic, first proposed in MQV and also used in Kim, to get a modified new ID-2-AK protocol. On second thoughts, we give another ID-2-AK protocol utilizing the operation of addition in finite field like our forenamed 2-AK protocol. The two ID-2-AK protocols are in possession of all the desired security attributes. We also compare our new protocols with others in terms of computational cost and security properties.
A New Efficient ID-Based Authenticated Key Agreement Protocol
Quan Yuan Songping Li
Recently Eun-Kyung Ryu, Eun-Jun Yoon, and Kee-Young Yoo proposed an efficient ID-based authenticated key agreement with paring.They argued that it is secure and efficient. In this paper, we show this protocol is doesn't satisfy the Key-Compromise Impersonate property and it is not secure against key reveal attack. Then we propose our protocol from this protocol and shim's protocol, its security and efficiency was analyzed.


Songping Li (2)
Jin Li (1)
Puwen Wei (1)
Yuliang Zheng (1)