报告题目：Automatic Search of Meet-in-the-Middle Preimage Attacks on AES-like Hashing
主讲人：史丹萍副研究员
报告时间：2021-5-27 （星期四）13：50-14：35
报告地点：教三楼 233教室
Bio：
史丹萍，中国科学院信息工程研究所副研究员，入选中国密码学会第六届“青年托举”项目，密码学会第三届青年工作委员会委员。长期从事对称密码的设计与自动化分析，研究成果发表在 CRYPTO、ASIACRYPT，FSE 等著名密码学会议上。
Abstract：
The Meet-in-the-Middle (MITM) preimage attack is highly effective in breaking the preimage resistance of many hash functions, including but not limited to the full MD5, HAVAL, and Tiger, and reduced SHA-0/1/2. It was also shown to be a threat to hash functions built on block ciphers like AES by Sasaki in 2011. Recently, such attacks on AES hashing modes evolved from merely using the freedom of choosing the internal state to also exploiting the freedom of choosing the message state. However, detecting such attacks especially those evolved variants is difficult. In previous works, the search space of the configurations of such attacks is limited, such that manual analysis is practical, which results in sub-optimal solutions. In this paper, we remove artificial limitations in previous works, formulate the essential ideas of the construction of the attack in well-defined ways, and translate the problem of searching for the best attacks into optimization problems under constraints in Mixed-Integer-Linear-Programming (MILP) models. The MILP models capture a large solution space of valid attacks; and the objectives of the MILP models are attack configurations with the minimized computational complexity. With such MILP models and using the off-the-shelf solver, it is efficient to search for the best attacks exhaustively. As a result, we obtain the first attacks against the full (5-round) and an extended (5.5- round) version of Haraka-512 v2, and 8-round AES-128 hashing modes, as well as improved attacks covering more rounds of Haraka-256 v2 and other members of AES and Rijndael hashing modes.
