Re: Checksum and transform layering

[Claudio Martins <ctpm@ist.utl.pt>]

On Thursday 06 November 2008, Gregory Maxwell wrote:
>
> While this has the advantages that the checksum does not have to be
> changed as transformations are changed and the system might catch
> errors in the compression layer, this design decision will be
> problematic if/when encryption is supported:  Plaintext checksums
> would leak substantial amounts of information about the content of
> files.  The system could be switched to a keyed cryptographic hash,

 Indeed. The most obvious (and quite trivial) attack one can do is buil=
d a=20
huge database of checksums for known files or chunks of files.

 AFAIK this has already been done by law enforcement/security agencies =
to=20
detect "illegal" files, so it's definitely an issue that would affect a=
ny=20
future encryption code implemented in btrfs.

Regards

Cl=C3=A1udio

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