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To: python-list@python.org
From: Randall Smith <randall@tnr.cc>
Subject: Re: Pure Python Data Mangling or Encrypting
Date: Sat, 27 Jun 2015 13:17:09 -0500
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Xref: csiph.com comp.lang.python:93256

On 06/27/2015 03:29 AM, Peter Otten wrote:


> Would it be sufficient to prepend the chunk with one block, say, of random
> data? To unmangle you'd just strip off that block.
>
> BLOCK = os.urandom(BLOCKSIZE)
>
> def mangle(source, dest):
>      dest.write(BLOCK)
>      shutil.copyfileobj(source, dest)
>
> def unmangle(source, dest):
>      source.read(BLOCKSIZE)
>      shutil.copyfileobj(source, dest)
>
> Disclaimer: I did not follow the ongoing discussion.
>

That is happening as a side effect.  Though not completely random, after 
running the data through a translation table, the 256 byte table is 
prepended.  Then a 4 byte checksum is calculated and prepended.

-Randall