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On Wednesday 19 December 2001 14:29, Jerome Etienne wrote:
> On Wed, Dec 19, 2001 at 11:51:43AM +0100, Gisle S{lensminde wrote:
> > Yes, this is a problem with loopback crypto. The problem is that
> > the loopback interface assume that it's length preserving,
>
> can you explain the rationnal behind such assumption ?
<snip>
Loopback transforms are block transformations. They act upon the blocks
of a block device. You cannot alter the size of blocks
Well, theoretically, you could make the input block size different from
the output block size, but since both the HD's and the linux kernel
have hard-coded (a minimum of) 512 byte blocks, you could only increase
or decrease those sizes by an amount of at least 512 bytes. Worse:
block sizes are assumed to be powers of 2 (except in special cases like
audio CD's which aren't handled by the normal block device layers,
AFAIK). So you can't go and take e.g. 32k clusters and append to each
one a 512 byte block to hold the MAC.
Marc
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Linux-crypto: cryptography in and on the Linux system
Archive: http://mail.nl.linux.org/linux-crypto/
