# Can XEX or XTS modes be used with only one tweak? (part 2)

This question is similar to Can XEX or XTS modes be used with only one tweak? except I am interested to know if one can instead use

$$X = E_{k}(0) \otimes \alpha^j \\ C = E_{k}(P \oplus X) \oplus X$$

in order to simply do a finite field multiplication and an aes operation per block rather than two aes operations per block (unlike the original question) for large amount of data.

• Note that the standard computation strategy for these modes is to compute the $E_k(I)$ once per sector and then compute $\alpha^j$ per-block which is a single multiplication of $\alpha^{j-1}\otimes \alpha$ with the left side being from the previous block. – SEJPM Oct 21 at 21:26
• @SEJPM in this instance you would compute $E_k(I)$ once per filesystem. Assuming 512-byte sectors, in order to access the 4th block of the 3rd sector you would have a j of 100 and an I of 0. – Post as a guest Oct 21 at 23:01