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SubjectRe: A patch to loop.c for better cryption support
Andi Kleen wrote:
>
> On Fri, Oct 13, 2000 at 05:04:08PM +0000, Marc Mutz wrote:
> > Andi Kleen wrote:
> > >
> > <snip>
> > > 2.4 has already broken backwards compatibility to 2.2 (IV changed
> > > from disk absolute to relative). When you change it now (before 2.4.0)
> > > it is relatively painless. I think the change is a good idea.
> > <snip>
> >
> > You're wrong. All kernels from int-2.2.10.4 onwards can be configured to
> > use relative block numbers as IV's. Both the FAQ in Documentation/crypto
> > and my HOWTO suggest to set CONFIG_BLK_DEV_LOOP_USE_REL_BLOCK to 'y'.
>
> That is not a standard kernel option. I'm not talking about any unofficial
> patchkits like the i* patches, just about what the standard loop device does.
> An encryption module can be backwards compatible itself by mapping the blocks
> itself, but without changes it will have an incompatible on disk format.
>

This thread was about encryption. And it was about IV's. The only
encryption that vanilla loop.c (from 2.2.17) offers is 'none' and 'xor'.
None is just that: a no-op. And xor does not use an IV. So the only
ciphers that could possibly have been adressed by this patch are the
ones in the kerneli patch. So the on-disk format did _not_ change
between recent int-2.2.x.y kernels and 2.4-testx, provided the user
followed the recommendations and used the previously mentioned option to
use relative block numbers as IV's.

Marc

--
Marc Mutz <Marc@Mutz.com> http://EncryptionHOWTO.sourceforge.net/
University of Bielefeld, Dep. of Mathematics / Dep. of Physics

PGP-keyID's: 0xd46ce9ab (RSA), 0x7ae55b9e (DSS/DH)


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