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Re: AW: AW: Hello and DVD-ROM encryption
Jari Ruusu wrote:
Peter_22@xxxxxx wrote:
Jari Ruusu <jariruusu@xxxxxxxxxxxxxxxxxxxxx> wrote:
Identical ciphertexts leak information.
I must admit, I didn´t get that. Mkisofs -r dirtree builds an ISO image
which I pipe through aespipe. You mean I shouldn´t use one keyfile twice
for doing this?
If same key file is used for multiple partitions, then adversary can easily
detect what sectors are identical on different partitions. Identical
plaintext data on different sectors on same file system are not a problem
because sector number is used in IV computation, and sector number is
guaranteed to be unique on one file system.
Wouldn't this be negated by the fact that you're initialising the
storage space for the ISO with /dev/urandom? This would be a fairly
good guarantee that blank sectors (the most likely things to be
identical) are going to still be different. I thought ISO images
wouldn't include any unused blocks, anyway, which would also mean that
blank sectors would be irrelevant.
And therefore, if you're not writing identical files in identical
locations, isn't the risk associated with reusing a set of keys reduced?
Another way of going about this might be to write a file from
/dev/urandom at the size you want and set this up as an loop-AES file
system. Copy your files on and then unmount it. Then copy this
encrypted filesystem onto the disk. When you want to access it, just
use aespipe or loop-AES (not sure which, given the earlier argument
about blocksizes) to open that file as a filesystem. Why try to encrypt
the ISO image at all?
Have fun,
Paul
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-- Paul Wayper at ANU - +61 2 6125 0643
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Linux-crypto: cryptography in and on the Linux system
Archive: http://mail.nl.linux.org/linux-crypto/