Re: Using compression before encryption in device-mapper
From: Bill Davidsen
Date: Wed Apr 14 2004 - 12:29:23 EST
On Wed, 14 Apr 2004, Paulo Marques wrote:
> Guillaume Lacôte wrote:
>
> >>>Oops ! I thought it was possible to guarantee with the Huffman encoding
> >>>(which is more basic than Lempev-Zif) that the compressed data use no
> >>>more than 1 bit for every byte (i.e. 12,5% more space).
>
> WTF??
>
> Zlib gives a maximum increase of 0.1% + 12 bytes (from the zlib manual), which
> for a 512 block will be a 2.4% guaranteed increase.
>
> I think that zlib already does the "if this is bigger than original, just mark
> the block type as uncompressed" algorithm internally, so the increase is minimal
> in the worst case.
I kind of think that the compression, even negative, is wanted here to
assist in obfuscation.
--
bill davidsen <davidsen@xxxxxxx>
CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.
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