International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Libo Wang

Publications

Year
Venue
Title
2023
EUROCRYPT
Coefficient Grouping: Breaking Chaghri and More
We propose an efficient technique called coefficient grouping to evaluate the algebraic degree of the FHE-friendly cipher Chaghri, which has been accepted for ACM CCS 2022. It is found that the algebraic degree increases linearly rather than exponentially. As a consequence, we can construct a 13-round distinguisher with time and data complexity of $2^{63}$ and mount a 13.5-round key-recovery attack. In particular, a higher-order differential attack on 8 rounds of Chaghri can be achieved with time and data complexity of $2^{38}$. Hence, it indicates that the full 8 rounds are far from being secure. Furthermore, we also demonstrate the application of our coefficient grouping technique to the design of secure cryptographic components. As a result, a countermeasure is found for Chaghri and it has little overhead compared with the original design. Since more and more symmetric primitives defined over a large finite field are emerging, we believe our new technique can have more applications in the future research.

Coauthors

Ravi Anand (1)
Takanori Isobe (1)
Fukang Liu (1)
Willi Meier (1)