[dm-crypt] inner workings of block mode encryption

U.Mutlu for-gmane at mutluit.com
Sun Feb 8 15:06:49 CET 2015


Hi,
I'm interessted in the inner workings of encrypting block devices
like the encrypted volumes created with the cryptsetup tool.

Let's say a file of size 200K is stored on an encrypted ext2 filesystem.
How is the enrcyption key applied to it?

I guess the password is used only for accessing/mounting the volume,
and the key is only a starting value (ie. a "seed") for the underlying cipher.

Since in these cases usually a blockwise operating cipher is used,
that means that the file will be encrypted of course blockwise,
for example in blocks of 32 bytes.

Now the question: are the blocks of that file all encrypted using the
same one key? Or does a kind of "streaming" or HMAC get used for the
subsequent blocks of the file?

-- 
TIA
Uenal



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