Re: [PATCH 0/2] crypto: talitos: Add AES-XTS mode

On Mon, Mar 9, 2015 at 6:16 AM, Horia Geant=C4=83 <horia.geanta@freescale.c=
om> wrote:

On 3/3/2015 7:44 PM, Martin Hicks wrote:

quoted

On Tue, Mar 3, 2015 at 10:44 AM, Horia Geant=C4=83
[off-list ref] wrote:

quoted

For talitos, there are two cases:

1. request data size is <=3D data unit / sector size
talitos can handle any IV / tweak scheme

2. request data size > sector size
since talitos internally generates the IV for the next sector by
incrementing the previous IV, only IV schemes that allocate consecutive
IV to consecutive sectors will function correctly.

it's not clear to me that #1 is right.  I guess it could be, but the
IV length would be limited to 8 bytes.

Yes, there's a limitation in talitos wrt. XTS IV / tweak size - it's up
to 8 bytes.
So I guess ESSIV won't work with talitos-xts, since the encrypted IV
output is 16 bytes.
But as previously said, ESSIV breaks the XTS standard requirement for
having a consecutive IV for consecutive blocks. ESSIV should really be
used only with disk-level encryption schemes that require an
unpredictable IV.

Ok.  I'll verify that the second half of the IV is zeroed.

One last thing that I'm not sure of is what string to place in
cra_ablkcipher.geniv field.   "eseqiv" seems wrong if plain/plain64
are the IVs that XTS is designed for.

Thanks,
mh

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Martin Hicks P.Eng.      |         mort@bork.org
Bork Consulting Inc.     |   +1 (613) 266-2296