# XTS-AES key management

XTS-AES uses two keys $(k_1, k_2)$, which are obtained from a concatenated key $k$. Does this key $k$ remain same for the whole disk or changes per sector?

• I can't write a full answer right now: $k$ remains the same for the whole disk. – SEJPM Oct 23 '15 at 7:22

$$C=E_{k_1}(P\oplus(E_{k_2}(n)\otimes\alpha^i))\oplus(E_{k_2}(n)\otimes\alpha^i)$$
With $\oplus$ denoting bitwise XOR, $n$ denoting the sector index, $i$ denoting the block index within the sector. $\alpha$ is a polynomial in the $GF(2^{128})$ and is exponentiated appropriately and multiplied ($\otimes$) with the encrypted sector index.
As you can see you don't need to alter either the key $k_1$ or $k_2$ for each sector as the indices will introduce a unique whitening value for each block.