Re: [PATCH 01/04] Adding cipher mode context information to crypto_tfm

[James Morris]

On Thu, 10 Feb 2005, Fruhwirth Clemens wrote:

> Because a tweak is different from an IV. There can be an arbitrary
> number of tweaks. For instance, EME takes 1 tweak per 512 bytes. If you
> have a 4k page to encrypt, you have to process 8 tweaks of whatever
> size. 
>  Therefore, you need 3 scatterlists: src, dst and the running along
> tweak.

The purpose of the scatterlists is to be able to process discontigous data 
at the page level.

The tweak, as I understand it, is something which you generate, and it is 
not inherently likely to be page-level clumps of data.  It does not ever 
need to be kmapped.

What you really need to do is use an array for the tweak (or possibly a
structure which maintains state about it if needed).


- James
-- 
James Morris
<jmorris@xxxxxxxxxx>


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