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

[Martin Hicks]

On Tue, Mar 3, 2015 at 10:44 AM, Horia Geantă
<horia.geanta at freescale.com> wrote:
> On 3/3/2015 12:09 AM, Martin Hicks wrote:
>>
>> On Mon, Mar 02, 2015 at 03:37:28PM +0100, Milan Broz wrote:
>>>
>>> If crypto API allows to encrypt more sectors in one run
>>> (handling IV internally) dmcrypt can be modified of course.
>>>
>>> But do not forget we can use another IV (not only sequential number)
>>> e.g. ESSIV with XTS as well (even if it doesn't make much sense, some people
>>> are using it).
>>
>> Interesting, I'd not considered using XTS with an IV other than plain/64.
>> The talitos hardware would not support aes/xts in any mode other than
>> plain/plain64 I don't think...Although perhaps you could push in an 8-byte
>> IV and the hardware would interpret it as the sector #.
>>
>
> For talitos, there are two cases:
>
> 1. request data size is <= 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.

This also points out that claiming that the XTS IV size is 16 bytes,
as my current patch does, could be problematic.  It's handy because
the first 8 bytes should contain a plain64 sector #, and the second
u64 can be used to encode the sector size but it would be a mistake
for someone to use the second 8 bytes for the rest of a 16byte IV.

mh

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