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Re: Pure Python Data Mangling or Encrypting

References (4 earlier) <mailman.42.1435206516.3674.python-list@python.org> <558bc912$0$2899$c3e8da3$76491128@news.astraweb.com> <slrnmonkip.1nu.jon+usenet@frosty.unequivocal.co.uk> <558c1a7e$0$1668$c3e8da3$5496439d@news.astraweb.com> <slrnmoo7ev.1nu.jon+usenet@frosty.unequivocal.co.uk>
Date 2015-06-26 10:33 +1000
Subject Re: Pure Python Data Mangling or Encrypting
From Chris Angelico <rosuav@gmail.com>
Newsgroups comp.lang.python
Message-ID <mailman.87.1435278799.3674.python-list@python.org> (permalink)

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On Fri, Jun 26, 2015 at 1:26 AM, Jon Ribbens
<jon+usenet@unequivocal.co.uk> wrote:
>> There are only 256 possible values for n, one of which doesn't transform the
>> data at all (ROT-0). If you're thinking of attacking this by pencil and
>> paper, 255 transformations sounds like a lot. For a computer, that's barely
>> harder than a single transformation.
>
> Well, it means you need to send 256 times as much data, which is a
> start. If you're instead using a 256-byte translation table then
> an attack becomes utterly impractical.
>

Utterly impractical? Maybe, if you attempt a pure brute-force approach
- there are 256! possible translation tables, which is roughly e500
attempts [1], and at roughly four a microsecond [2] that'd still take
a ridiculously long time. But there are two gigantic optimizations you
could do. Firstly, there are frequency-based attacks, and byte value
duplicates will tell you a lot - classic cryptographic work. And
secondly, you can simply take the first few bytes of a file - let's
say 16, although a lot of files can be recognized in less than that.
Even if there are no duplicate bytes, that'd be a maximum of 16!
translation tables that truly matter, or just 2e13. At the same speed,
that makes about a million seconds of computing time required. Divide
that across a bunch of separate computers (the job is embarrassingly
parallel after all), and you could get that result pretty easily. Cut
the prefix to just 8 bytes and you have a mere 40K encryption keys to
try - so quick that you wouldn't even see it happen. Nope, a simple
substitution cipher is still not secure. Even the famous Enigma
machine was a lot more than just letter-for-letter substitution - a
double letter in the cleartext wouldn't be represented by a double
letter in the result - and once the machine's secrets were figured
out, the day's key could be reassembled fairly readily.

ChrisA

[1] It's actually closer to 8.6e506, if you care.
[2] timeit result from my laptop - you could do better, but that's a
reasonable average

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Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-24 13:36 -0500
  Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-06-25 14:07 +1000
    Re: Pure Python Data Mangling or Encrypting Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-24 21:27 -0700
      Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-25 19:25 +1000
        Re: Pure Python Data Mangling or Encrypting Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-25 02:41 -0700
        Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-06-25 19:57 +1000
        Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-25 10:03 +0000
          Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-06-26 01:13 +1000
            Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-25 15:26 +0000
              Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-25 13:58 -0500
              Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-06-26 10:33 +1000
                Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-26 10:49 +0000
              Re: Pure Python Data Mangling or Encrypting Ian Kelly <ian.g.kelly@gmail.com> - 2015-06-25 19:01 -0600
                Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-06-27 03:06 +1000
                Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-26 15:09 -0500
                Re: Pure Python Data Mangling or Encrypting Johannes Bauer <dfnsonfsduifb@gmx.de> - 2015-06-26 23:07 +0200
                Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-26 21:29 +0000
                Re: Pure Python Data Mangling or Encrypting Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-26 22:55 +0100
                Re: Pure Python Data Mangling or Encrypting Johannes Bauer <dfnsonfsduifb@gmx.de> - 2015-06-27 00:42 +0200
                Re: Pure Python Data Mangling or Encrypting Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-26 16:26 -0700
                Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-27 00:21 +0000
                Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-26 19:55 -0500
                Re: Pure Python Data Mangling or Encrypting Johannes Bauer <dfnsonfsduifb@gmx.de> - 2015-06-27 07:24 +0200
                Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-26 19:12 -0500
                Re: Pure Python Data Mangling or Encrypting Ian Kelly <ian.g.kelly@gmail.com> - 2015-06-26 15:58 -0600
                Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-26 19:23 -0500
                Re: Pure Python Data Mangling or Encrypting Johannes Bauer <dfnsonfsduifb@gmx.de> - 2015-06-26 23:11 +0200
                Re: Pure Python Data Mangling or Encrypting Michael Torrie <torriem@gmail.com> - 2015-06-27 11:02 -0600
                Re: Pure Python Data Mangling or Encrypting Paul Rubin <no.email@nospam.invalid> - 2015-06-27 10:45 -0700
                Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-06-27 13:38 +1000
                Re: Pure Python Data Mangling or Encrypting Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-26 21:05 -0700
                Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-06-27 16:16 +1000
                Re: Pure Python Data Mangling or Encrypting Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-27 13:30 -0700
                Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-06-28 11:18 +1000
                Re: Pure Python Data Mangling or Encrypting Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-27 19:11 -0700
                Re: Pure Python Data Mangling or Encrypting Ian Kelly <ian.g.kelly@gmail.com> - 2015-06-26 23:47 -0600
                Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-06-27 18:38 +1000
                Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-06-27 18:53 +1000
                Re: Pure Python Data Mangling or Encrypting Johannes Bauer <dfnsonfsduifb@gmx.de> - 2015-06-27 11:07 +0200
                Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-06-27 19:17 +1000
                Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-27 09:27 +0000
                Re: Pure Python Data Mangling or Encrypting Johannes Bauer <dfnsonfsduifb@gmx.de> - 2015-06-27 12:05 +0200
                Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-06-27 20:16 +1000
                Re: Pure Python Data Mangling or Encrypting Johannes Bauer <dfnsonfsduifb@gmx.de> - 2015-06-27 12:55 +0200
                Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-27 10:26 +0000
                Re: Pure Python Data Mangling or Encrypting Laura Creighton <lac@openend.se> - 2015-06-27 14:27 +0200
                Re: Pure Python Data Mangling or Encrypting Johannes Bauer <dfnsonfsduifb@gmx.de> - 2015-06-27 12:18 +0200
                Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-06-27 21:33 +1000
                Re: Pure Python Data Mangling or Encrypting Ian Kelly <ian.g.kelly@gmail.com> - 2015-06-27 08:59 -0600
                Re: Pure Python Data Mangling or Encrypting Laura Creighton <lac@openend.se> - 2015-06-27 13:25 +0200
                Re: Pure Python Data Mangling or Encrypting Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2015-06-27 15:23 +0300
                Re: Pure Python Data Mangling or Encrypting Laura Creighton <lac@openend.se> - 2015-06-27 14:48 +0200
                Re: Pure Python Data Mangling or Encrypting Johannes Bauer <dfnsonfsduifb@gmx.de> - 2015-06-27 11:12 +0200
                Re: Pure Python Data Mangling or Encrypting Ian Kelly <ian.g.kelly@gmail.com> - 2015-06-27 09:09 -0600
                Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-06-28 03:35 +1000
                Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-06-28 03:58 +1000
                Re: Pure Python Data Mangling or Encrypting Ian Kelly <ian.g.kelly@gmail.com> - 2015-06-27 14:16 -0600
                Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-28 13:41 +0000
                Re: Pure Python Data Mangling or Encrypting Robert Kern <robert.kern@gmail.com> - 2015-06-27 08:58 +0100
                Re: Pure Python Data Mangling or Encrypting Robert Kern <robert.kern@gmail.com> - 2015-06-27 09:07 +0100
                Re: Pure Python Data Mangling or Encrypting Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-06-27 10:39 -0400
                Re: Pure Python Data Mangling or Encrypting Grant Edwards <invalid@invalid.invalid> - 2015-06-27 12:38 +0000
                Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-27 13:22 -0500
                Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-06-28 04:51 +1000
                Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-06-28 09:05 +1000
                Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-06-27 11:21 +1000
                Re: Pure Python Data Mangling or Encrypting Ian Kelly <ian.g.kelly@gmail.com> - 2015-06-26 23:59 -0600
                Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-27 09:26 +0000
                Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-06-27 16:52 +1000
                Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-27 12:08 -0500
                Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-06-28 04:50 +1000
                Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-29 15:52 -0500
                Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-06-30 13:00 +1000
                Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-30 12:19 +0000
                Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-07-01 04:17 +1000
                Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-07-01 04:33 +1000
                Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-30 18:37 +0000
                Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-07-01 09:38 -0500
                Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-30 12:39 -0500
                Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve@pearwood.info> - 2015-07-01 04:59 +1000
                Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-07-01 05:20 +1000
                Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-30 23:25 +0000
                Re: Pure Python Data Mangling or Encrypting alister <alister.nospam.ware@ntlworld.com> - 2015-07-01 08:06 +0000
                Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-28 14:21 +0000
                Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-29 15:46 -0500
                Re: Pure Python Data Mangling or Encrypting Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-06-29 20:49 +0000
                Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-30 12:43 -0500
                Re: Pure Python Data Mangling or Encrypting Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-07-02 10:31 +1200
              Re: Pure Python Data Mangling or Encrypting Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-26 02:17 +0100
              Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-06-26 12:06 +1000
              Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-06-26 12:05 +1000
              Re: Pure Python Data Mangling or Encrypting Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-26 03:24 +0100
              Re: Pure Python Data Mangling or Encrypting Chris Angelico <rosuav@gmail.com> - 2015-06-26 12:29 +1000
        Re: Pure Python Data Mangling or Encrypting Joonas Liik <liik.joonas@gmail.com> - 2015-06-25 13:00 +0300
        Re: Pure Python Data Mangling or Encrypting Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-25 03:18 -0700
    Re: Pure Python Data Mangling or Encrypting Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-25 17:05 +1000
    Re: Pure Python Data Mangling or Encrypting Randall Smith <randall@tnr.cc> - 2015-06-25 14:09 -0500

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