CSKH-02.2017 - (Abstract) Encryption on a storage device has characteristics that some common block cipher mode of operation such as CBC, CFB, CTR,… are not reach; so the tweakable block cipher notation was introduced. LRW construction was proposed by Liskov, Rivest and Wagner [1], is one of the most popular methods in constructing tweakable block cipher. In this paper, we consider the indistinguishability of LRW and XEX2 constructions. Specifically, we confirm the results in LRW construction’s initial proof, and then the indistinguishability of XEX2 is evaluated in detail. Ours results improve the security bound for LRW and XEX2 construction.