dm-crypt overhead

[Lukáš Pohanka <numberfour@xxxxxxxxx>]

I have a couple of questions regarding dm-crypt and overhead when using different encryption algorithms.

Firstly, am I right that the aes-xts-plain64 algorithm has no overhead, i.e. the size occupied at the target device is exactly the same as it would be without the dm-crypt layer?

Secondly, when using aes-gcm, is the authentication tag created per-sector? This means in this case there is an overhead per each sector (depending on the tag size)?

Also I couldn't find how the IV is calculated in case of aes-gcm, can also -plain64 be used?

Thanks in advance for clarifications.

Lukas

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