Re: How long will this take?

From	David Wright <deblis@lionunicorn.co.uk>
Newsgroups	linux.debian.user
Subject	Re: How long will this take?
Date	2020-06-27 03:30 +0200
Message-ID	<Am7Pk-4K4-3@gated-at.bofh.it> (permalink)
References	(5 earlier) <AgQvL-dQ-5@gated-at.bofh.it> <AjeNk-5w4-3@gated-at.bofh.it> <Ajxdg-7ZC-5@gated-at.bofh.it> <AlWhc-6iS-7@gated-at.bofh.it> <Am4HM-2Yc-5@gated-at.bofh.it>
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On Fri 26 Jun 2020 at 15:06:31 (-0700), David Christensen wrote:
> On 2020-06-26 06:07, David Wright wrote:
> > On Fri 19 Jun 2020 at 14:52:11 (-0700), David Christensen wrote:
> 
> > > Benchmark is one thing.  But, from a security viewpoint, writing zeros
> > > to an encrypted volume amounts to providing blocks of plaintext for
> > > corresponding blocks of cyphertext, thereby facilitating
> > > cryptanalysis.
> > 
> > So in view of the unlikelihood of badblocks actually logging something
> > more useful than SMART (where available) or normal disk write errors,
> > perhaps a compromise (for my use case) is to just write /dev/urandom
> > rather than /dev/zero.
> 
> Copying random data to a partition while creating an encrypted
> filesystem provides a high-entropy backdrop to conceal ciphertext
> blocks.  This is a form of steganography.  The Debian Installer manual
> partitioning page has an option to do this.

I presume you meet this option when you select "Configure encrypted volumes",
something that I've never done. Because currently I only encrypt /home
and swap, I set these up after installation, if they're not already there.

I must admit that I prefer to partition disks and set up encryption
outside the d-i, usually capturing the process with script.

> As the storage is used, the initial random blocks will be overwritten
> by ciphertext blocks.  Depending upon filesystem, encryption, volume
> management, and/or device details, the steganography degrades and may
> eventually disappear.
> 
> Copying random data to storage will add fresh nearly-random blocks on
> the device, improving the steganography.  (The canonical example is to
> copy /dev/urandom to a file until the filesystem fills up, and then
> delete the file.  But, this takes time and adds wear to the device.)

Yes, SSD caveat taken on board.

> > On this slow machine with an oldish PATA disk,
> > I can get about 75% speed from urandom, 15MB/s vs 20MB/s on a 29GiB
> > partition (no encryption). There's a noticeable slowdown because,
> > I presume, the machine runs a bit short of entropy after a while.
> 
> I think you are noticing a slowdown when the Linux write buffer fills.

I'm not sure where these write buffers might be hiding: the
2000-vintage PC has 512MB memory, and the same size swap partition,
though the latter is on a disk constructed one month earlier than the
target disk (Feb/Mar 2008). The target disk has 8MB of cache.
With a leisurely determination of dd's PID, my first USR1 poke
occurred no earlier than after 4GB of copying, over three minutes in.

Cheers,
David.

Thread

How long will this take? Matthew Campbell <trenix25@pm.me> - 2020-06-08 22:30 +0200
  Re: How long will this take? Dan Ritter <dsr@randomstring.org> - 2020-06-08 22:40 +0200
    Re: How long will this take? deloptes <deloptes@gmail.com> - 2020-06-08 23:00 +0200
      Re: How long will this take? Dan Ritter <dsr@randomstring.org> - 2020-06-09 00:10 +0200
        Re: How long will this take? Michael Stone <mstone@debian.org> - 2020-06-10 16:10 +0200
          Re: How long will this take? Michael Stone <mstone@debian.org> - 2020-06-10 17:00 +0200
          Re: How long will this take? Andrei POPESCU <andreimpopescu@gmail.com> - 2020-06-10 17:00 +0200
          Re: How long will this take? David Christensen <dpchrist@holgerdanske.com> - 2020-06-11 02:40 +0200
    Re: How long will this take? Jude DaShiell <jdashiel@panix.com> - 2020-06-09 02:20 +0200
      Re: How long will this take? Andrei POPESCU <andreimpopescu@gmail.com> - 2020-06-09 09:40 +0200
  Re: How long will this take? Nicolas George <george@nsup.org> - 2020-06-08 22:40 +0200
    Re: How long will this take? Matthew Campbell <trenix25@pm.me> - 2020-06-08 23:10 +0200
      Re: How long will this take? Nicolas George <george@nsup.org> - 2020-06-08 23:20 +0200
  Re: How long will this take? David Wright <deblis@lionunicorn.co.uk> - 2020-06-09 05:10 +0200
    Re: How long will this take? Christopher David Howie <me@chrishowie.com> - 2020-06-09 06:00 +0200
      Re: How long will this take? Nicolas George <george@nsup.org> - 2020-06-09 11:50 +0200
        Fw: How long will this take? Matthew Campbell <trenix25@pm.me> - 2020-06-09 17:40 +0200
        Re: How long will this take? Christopher David Howie <me@chrishowie.com> - 2020-06-10 02:50 +0200
    Re: How long will this take? Michael Stone <mstone@debian.org> - 2020-06-10 16:20 +0200
      Re: How long will this take? David Wright <deblis@lionunicorn.co.uk> - 2020-06-10 19:10 +0200
        Fw: How long will this take? Matthew Campbell <trenix25@pm.me> - 2020-06-10 19:20 +0200
          Re: Fw: How long will this take? David Christensen <dpchrist@holgerdanske.com> - 2020-06-11 03:10 +0200
            Fw: Fw: How long will this take? Matthew Campbell <trenix25@pm.me> - 2020-06-11 20:00 +0200
              Re: Fw: Fw: How long will this take? Dan Ritter <dsr@randomstring.org> - 2020-06-11 20:10 +0200
                Re: Fw: Fw: How long will this take? Kenneth Parker <sea7kenp@gmail.com> - 2020-06-11 22:20 +0200
                Re: Fw: Fw: How long will this take? "Rick Thomas" <rick.thomas@pobox.com> - 2020-06-13 11:20 +0200
        Re: How long will this take? Michael Stone <mstone@debian.org> - 2020-06-10 21:00 +0200
          [OT] How to help the OP? (was: How long will this take?) l0f4r0@tuta.io - 2020-06-10 21:30 +0200
            Re: [OT] How to help the OP? (was: How long will this take?) Nicolas George <george@nsup.org> - 2020-06-10 21:30 +0200
              Re: [OT] How to help the OP? (was: How long will this take?) Nicolas George <george@nsup.org> - 2020-06-10 22:00 +0200
                Re: [OT] How to help the OP? (was: How long will this take?) Michael Stone <mstone@debian.org> - 2020-06-10 22:00 +0200
                Re: [OT] How to help the OP? (was: How long will this take?) Nicolas George <george@nsup.org> - 2020-06-10 22:30 +0200
                Re: [OT] How to help the OP? (was: How long will this take?) deloptes <deloptes@gmail.com> - 2020-06-11 07:30 +0200
                Re: [OT] How to help the OP? (was: How long will this take?) <tomas@tuxteam.de> - 2020-06-11 07:50 +0200
                Re: [OT] How to help the OP? (was: How long will this take?) deloptes <deloptes@gmail.com> - 2020-06-11 11:00 +0200
                Re: [OT] How to help the OP? (was: How long will this take?) <tomas@tuxteam.de> - 2020-06-11 11:40 +0200
                Re: [OT] How to help the OP? (was: How long will this take?) Michael Stone <mstone@debian.org> - 2020-06-11 14:00 +0200
                Re: [OT] How to help the OP? (was: How long will this take?) Nicolas George <george@nsup.org> - 2020-06-11 14:10 +0200
              Re: [OT] How to help the OP? (was: How long will this take?) Michael Stone <mstone@debian.org> - 2020-06-10 22:00 +0200
            Re: [OT] How to help the OP? (was: How long will this take?) Michael Stone <mstone@debian.org> - 2020-06-10 21:50 +0200
              Re: [OT] How to help the OP? (was: How long will this take?) David Wright <deblis@lionunicorn.co.uk> - 2020-06-12 04:00 +0200
          Re: How long will this take? David Wright <deblis@lionunicorn.co.uk> - 2020-06-12 04:00 +0200
            Re: How long will this take? Michael Stone <mstone@debian.org> - 2020-06-12 14:00 +0200
              Re: How long will this take? David Wright <deblis@lionunicorn.co.uk> - 2020-06-19 04:20 +0200
                Re: How long will this take? David Christensen <dpchrist@holgerdanske.com> - 2020-06-20 00:00 +0200
                Re: How long will this take? David Wright <deblis@lionunicorn.co.uk> - 2020-06-26 15:10 +0200
                Re: How long will this take? David Christensen <dpchrist@holgerdanske.com> - 2020-06-27 00:10 +0200
                Re: How long will this take? David Wright <deblis@lionunicorn.co.uk> - 2020-06-27 03:30 +0200
                Re: How long will this take? David Christensen <dpchrist@holgerdanske.com> - 2020-06-27 05:00 +0200
                Re: How long will this take? David Wright <deblis@lionunicorn.co.uk> - 2020-07-02 03:10 +0200
  Re: How long will this take? David Christensen <dpchrist@holgerdanske.com> - 2020-06-09 09:10 +0200
  Re: How long will this take? l0f4r0@tuta.io - 2020-06-09 20:10 +0200
    Re: How long will this take? Nicolas George <george@nsup.org> - 2020-06-09 20:30 +0200
      Re: How long will this take? Jude DaShiell <jdashiel@panix.com> - 2020-06-09 21:50 +0200
        Re: How long will this take? Nicolas George <george@nsup.org> - 2020-06-09 21:50 +0200
      Re: How long will this take? Anders Andersson <pipatron@gmail.com> - 2020-06-10 12:50 +0200
        Re: How long will this take? Nicolas George <george@nsup.org> - 2020-06-10 13:20 +0200
          Re: How long will this take? Anders Andersson <pipatron@gmail.com> - 2020-06-10 15:30 +0200
            Re: How long will this take? Nicolas George <george@nsup.org> - 2020-06-10 15:40 +0200
              Re: How long will this take? Anders Andersson <pipatron@gmail.com> - 2020-06-10 16:00 +0200
                Re: How long will this take? Nicolas George <george@nsup.org> - 2020-06-10 16:10 +0200
                Re: How long will this take? Anders Andersson <pipatron@gmail.com> - 2020-06-10 22:10 +0200
                Fw: How long will this take? Matthew Campbell <trenix25@pm.me> - 2020-06-10 19:00 +0200
    Re: How long will this take? Jude DaShiell <jdashiel@panix.com> - 2020-06-09 20:30 +0200
  Re: How long will this take? Seeds Notoneofmy <notoneofmyseeds@gmx.de> - 2020-06-27 01:40 +0200
    Re: How long will this take? rhkramer@gmail.com - 2020-06-27 03:30 +0200
      Re: How long will this take? Seeds Notoneofmy <notoneofmyseeds@gmx.de> - 2020-06-27 03:50 +0200
        Re: How long will this take? rhkramer@gmail.com - 2020-06-27 20:10 +0200
    Re: How long will this take? Andrei POPESCU <andreimpopescu@gmail.com> - 2020-06-27 10:40 +0200
    On Subject drift [was: How long will this take?] <tomas@tuxteam.de> - 2020-06-27 11:00 +0200
      Re: On Subject drift [was: How long will this take?] l0f4r0@tuta.io - 2020-06-27 11:40 +0200
      Re: On Subject drift [was: How long will this take?] Seeds Notoneofmy <notoneofmyseeds@gmx.de> - 2020-06-27 16:40 +0200
        Re: On Subject drift [was: How long will this take?] <tomas@tuxteam.de> - 2020-06-27 18:50 +0200

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