Abstract: Key agreement is an important mean to realize the secure communication between participants under the open and fair environment. Recently, Alvarez et al proposes a novel key agreement protocol, the session key in this protocol is generated by multiplying powers of block triangular matrices. The research in this paper finds that the original protocol is insecure since that the security parameter in Alvarez’s scheme can be obtained by solving a set of linear equations, it analyzes this protocol carefully and proposes a novel practical attack method. It is worth mentioning that this attack method can be used in the similar key agreement protocols based on the block triangular matrices technology.

Key words: cryptography, key agreement, triangular matrix, cryptanalysis, non-Abelian group

摘要： 密钥协商是实现参与者在公平的开放环境下建立会话密钥的重要手段。最近，Alvarez等人提出了一种新的密钥协商协议，该协议的会话密钥是通过分块上三角矩阵的幂乘得到的。但研究发现，该协议并不安全，其安全参数可以简单地通过计算一个方程组来获得。详细分析了该协议，并提出了一种切实可行的攻击方法，而且该方法可以推广到使用类似技术设计的密钥协商协议中。

关键词: 密码学, 密钥协商, 三角矩阵, 密码分析, 非阿贝尔群