[Resource Topic] 2023/776: Quantum Attacks on Type-1 Generalized Feistel Schemes

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Quantum Attacks on Type-1 Generalized Feistel Schemes

Authors: Hong-Wei Sun, Bin-Bin Cai, Su-Juan Qin, Qiao-Yan Wen, Fei Gao


Generalized Feistel schemes (GFSs) are extremely important and extensively researched cryptographic schemes. In this paper, we investigate the security of Type-1 GFS in quantum circumstances. On the one hand, in the qCCA setting, we give a new quantum polynomial time distinguisher on (d^2 -1)-round Type-1 GFS with branches d >3, which extends the previous results by d-2 rounds. This leads to a more efficient analysis of type-1 GFS, that is, the complexity of some previous key-recovery attacks is reduced by a factor of 2^(((d-2)k)/2), where k is the key length of the internal round function. On the other hand, for CAST-256, which is a certain block cipher based on Type-1 GFS, we give a 17-round quantum distinguisher in the qCPA setting. As a result, we construct an r(r > 17) round quantum key-recovery attack with complexity O(2^(37(r-17))/2 ).

ePrint: https://eprint.iacr.org/2023/776

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