A STUDY ON SPACE-HARD WHITE-BOX CRYPTOGRAPHY

Date

2023-7-20

Author

Güner, Hatice Kübra

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Protecting secret keys from malicious observers is a major problem for cryptographic algorithms in untrusted environments. White-box cryptography suggests hiding the key in the cipher code with an appropriate method such that extracting the key be- comes impossible in the white-box setting. The key is generally embedded into the confusion layer with suitable methods. One of them is using encoding techniques. Nevertheless, many encoding methods are vulnerable to algebraic attacks and side- channel analysis. Another is the space hardness concept, which creates large lookup tables that cannot be easily extracted from the device. In (M,Z)-space hard algorithms, the secret key is embedded in large tables created as a substitution box with a suitable block cipher. So the key extraction problem in the white-box setting turns into a key recovery problem in the black-box case. One of the main issues in (M,Z)-space hard algorithms is accelerating the run-time of the white-box/black-box implementation. In this study, we aim to use the advantage of the efficiency of lightweight compo- nents to speed up the diffusion layer of white-box algorithms without decreasing the security size. Therefore, we compare the linear layer of NIST Lightweight Standard- ization candidates for efficiency and suitability to white-box settings in existing space hard ciphers. The performance results of the algorithms are compared with WARX and SPNbox. According to the results, using the lightweight components in the diffu- sion layer accelerates the performance of white-box algorithms by at least 16%. Ad- ditionally, we propose an LS-design based white-box algorithm with better run-rime performance and an LS-design based table creation method to take advantage of the bitslice implementation against side-channel attacks. When we compare the run-time performance of our method with the SPNbox algorithm, we obtain 28% improvement for white-box implementation and 27% for black-box implementation. At the same time, in the white-box setting, the LS-design based method is also implemented to the 256-bit block size.

Subject Keywords

White-box Cryptography, Software Protection, Space-hard Ciphers, Lightweight Components

URI

https://hdl.handle.net/11511/104883

Collections

Graduate School of Applied Mathematics, Thesis