At Thursday 21/12/2006 18:32, Fredrik Lundh wrote:
> Hi, I have some code that takes a string and obtains a compressed
> version using zlib.compress
>
> Does anybody know how I can remove the header portion of the compressed
> bytes, such that I only have the compressed data remaining?
what makes you think there's a "header portion" in the data you get
from zlib.compress ? it's just a continuous stream of bits, all of
which are needed by the decoder.
No. The first 2 bytes (or more if using a preset dictionary) are
header information. The last 4 bytes are for checksum. In-between
lies the encoded bit stream.
Using the default options ("deflate", default compression level, no
custom dictionary) will make those first two bytes 0x78 0x9c.
If you want to encrypt a compressed text, you must remove redundant
information first. Knowing part of the clear message is a security
hole. Using an structured container (like a zip/rar/... file) gets
worse because the fixed (or "guessable") part is longer, but anyway,
2 bytes may be bad enough.
See RFC1950 <ftp://ftp.isi.edu/in-notes/rfc1950.txt>
--
Gabriel Genellina
Softlab SRL
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