Universally Composable Forward Secure Dynamic Searchable Symmetric Encryption
Toshiya Shibata, Kazuki Yoneyama · 2021
Kurosawa et al. formulate a universally composable (UC) security definition of dynamic searchable symmetric encryption (DSSE). They also show (weak) equivalence between the UC and the game-based definition, and introduce a UC secure DSSE scheme (KSOY scheme). However, there is a problem in their update protocol such that just documents containing the same keyword can be modified. Hence, the KSOY scheme does not satisfy forward security which guarantees that the server cannot know any relationship between an added or modified document and past search queries. In this paper, we introduce a new DSSE scheme such that documents containing different keywords can be modified, by extending the KSOY scheme. In addition, since Kurosawa et al.'s UC definition does not guarantee forward security, we extend their UC definition to guarantee forward security, and prove (weak) equivalence between the game-based definition of forward security and our UC definition. We also show that the proposed scheme satisfies UC security by proving the game-based definition.