[dm-crypt] iv generation from third-party code

Arno Wagner arno at wagner.name
Thu May 7 12:09:47 CEST 2015

On Thu, May 07, 2015 at 11:36:49 CEST, Fraser Scott wrote:
> On 7 May 2015 at 10:29, Arno Wagner <arno at wagner.name> wrote:
> Yeah. I've got some limitations as to where I can keep a 400GB file, so for
> now I'll just work with a hundred meg or so. Once I can strings that to get
> what looks like a file system, I'll apply the code to the whole image.

Just get a 1TB or larger external USB disk. They are not expensive.
And probably a lot cheaper than your wive's wrath of you accidentally
kill the original disk. Firts rule of all data-recovery: Never work
on the original, always on a copy. And if the data has any worth,
make two backups and only work on one.
> Just one remark: Your terminology seems to be off, as ECB does not
> > have an IV. I suggets using the formula from Wikipedia directly and
> > to forget about "IV"s.
> >
> What I meant was I was using openssl's AES in ECB mode as a building block
> for doing LRW myself. So I was doing something like E_k(tweak(IV, sector))
> ^ tweak(IV, sector) with ECB providing E_k.

Ok. The thing is though that "ECB" is a "mode" while E_k is 
one elementary encryption op. ECB means encryting b0,b1,b2 as 
E_k(b0),E_k(b1),E_k(b2). For just one block, they are the same, 
but the term "mode" does not make sense for just one block.

Not trying to be a smart-ass, but people will understand you 
better with the right terminology.

Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
A good decision is based on knowledge and not on numbers. -- Plato

If it's in the news, don't worry about it.  The very definition of 
"news" is "something that hardly ever happens." -- Bruce Schneier

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