Re: Make a unique filesystem path, without creating the file

From	Jon Ribbens <jon+usenet@unequivocal.co.uk>
Newsgroups	comp.lang.python
Subject	Re: Make a unique filesystem path, without creating the file
Date	2016-02-23 00:44 +0000
Organization	A noiseless patient Spider
Message-ID	<slrnncnb1a.16b.jon+usenet@wintry.unequivocal.co.uk> (permalink)
References	(9 earlier) <56cb9bb5$0$1595$c3e8da3$5496439d@news.astraweb.com> <slrnncn8u3.16b.jon+usenet@wintry.unequivocal.co.uk> <mailman.55.1456186740.20994.python-list@python.org> <slrnncn9uc.16b.jon+usenet@wintry.unequivocal.co.uk> <mailman.57.1456187639.20994.python-list@python.org>

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On 2016-02-23, Chris Angelico <rosuav@gmail.com> wrote:
> On Tue, Feb 23, 2016 at 11:26 AM, Jon Ribbens
><jon+usenet@unequivocal.co.uk> wrote:
>> On 2016-02-23, Chris Angelico <rosuav@gmail.com> wrote:
>>> On Tue, Feb 23, 2016 at 11:08 AM, Jon Ribbens
>>><jon+usenet@unequivocal.co.uk> wrote:
>>>>> If you generate 2**128 + 1 such numbers, you are *guaranteed* to
>>>>
>>>> ... have expired due to the heat death of the universe.
>>>
>>> Maybe... but by the time you get to 2**64 of them, you have a 50%
>>> chance of a collision. (That's either utterly intuitive or completely
>>> counter-intuitive, depending on who you are.)
>>
>> Um, did you mean to say 2**127? Are you thinking of the
>> birthday paradox or something, which doesn't apply here?
>
> By the time you generate 2**64 of them, you have a 50% chance that
> some pair of them collides. Yes, the birthday paradox does apply here.

Oh, I see, you're thinking of it differently. I was thinking of it as
Alice is choosing a filename and Mallet is trying to guess it, in which
case the birthday paradox doesn't apply. You're thinking of it as Alice
is generating many random filenames and, even though she could avoid
collisions with 100% certainty by remembering what she's already had,
isn't doing so, and must avoid colliding with herself. I don't think
your version makes has much relevance as an attack model.

Thread

Re: Make a unique filesystem path, without creating the file Ethan Furman <ethan@stoneleaf.us> - 2016-02-22 10:11 -0800
  Re: Make a unique filesystem path, without creating the file Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-02-22 18:17 +0000
    Re: Make a unique filesystem path, without creating the file Chris Angelico <rosuav@gmail.com> - 2016-02-23 05:25 +1100
      Re: Make a unique filesystem path, without creating the file Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-02-22 18:39 +0000
        Re: Make a unique filesystem path, without creating the file Marko Rauhamaa <marko@pacujo.net> - 2016-02-22 20:48 +0200
          Re: Make a unique filesystem path, without creating the file Steven D'Aprano <steve@pearwood.info> - 2016-02-23 10:37 +1100
            Re: Make a unique filesystem path, without creating the file Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-02-23 00:08 +0000
              Re: Make a unique filesystem path, without creating the file Chris Angelico <rosuav@gmail.com> - 2016-02-23 11:18 +1100
                Re: Make a unique filesystem path, without creating the file Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-02-23 00:26 +0000
                Re: Make a unique filesystem path, without creating the file Chris Angelico <rosuav@gmail.com> - 2016-02-23 11:33 +1100
                Re: Make a unique filesystem path, without creating the file Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-02-23 00:44 +0000
                Re: Make a unique filesystem path, without creating the file Chris Angelico <rosuav@gmail.com> - 2016-02-23 11:56 +1100
        Re: Make a unique filesystem path, without creating the file Chris Angelico <rosuav@gmail.com> - 2016-02-23 06:04 +1100
          Re: Make a unique filesystem path, without creating the file Paul Rubin <no.email@nospam.invalid> - 2016-02-22 11:22 -0800
            Re: Make a unique filesystem path, without creating the file Steven D'Aprano <steve@pearwood.info> - 2016-02-23 10:45 +1100
          Re: Make a unique filesystem path, without creating the file Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-02-22 19:22 +0000
            Re: Make a unique filesystem path, without creating the file Marko Rauhamaa <marko@pacujo.net> - 2016-02-22 21:32 +0200
              Re: Make a unique filesystem path, without creating the file Random832 <random832@fastmail.com> - 2016-02-22 14:41 -0500
                Re: Make a unique filesystem path, without creating the file Marko Rauhamaa <marko@pacujo.net> - 2016-02-22 22:41 +0200
                Re: Make a unique filesystem path, without creating the file Paul Rubin <no.email@nospam.invalid> - 2016-02-22 13:05 -0800
                Re: Make a unique filesystem path, without creating the file Marko Rauhamaa <marko@pacujo.net> - 2016-02-22 23:22 +0200
                Re: Make a unique filesystem path, without creating the file Paul Rubin <no.email@nospam.invalid> - 2016-02-22 15:26 -0800
              Re: Make a unique filesystem path, without creating the file Steven D'Aprano <steve@pearwood.info> - 2016-02-23 11:33 +1100
                Re: Make a unique filesystem path, without creating the file Marko Rauhamaa <marko@pacujo.net> - 2016-02-23 08:54 +0200
                Re: Make a unique filesystem path, without creating the file Paul Rubin <no.email@nospam.invalid> - 2016-02-22 23:18 -0800
                Re: Make a unique filesystem path, without creating the file Marko Rauhamaa <marko@pacujo.net> - 2016-02-23 21:04 +0200
                Re: Make a unique filesystem path, without creating the file Steven D'Aprano <steve@pearwood.info> - 2016-02-24 12:40 +1100
                Re: Make a unique filesystem path, without creating the file Marko Rauhamaa <marko@pacujo.net> - 2016-02-24 09:20 +0200
                Re: Make a unique filesystem path, without creating the file Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-02-25 16:38 +1100
                Re: Make a unique filesystem path, without creating the file Marko Rauhamaa <marko@pacujo.net> - 2016-02-25 08:54 +0200
                Re: Make a unique filesystem path, without creating the file Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-02-25 19:21 +1100
                Re: Make a unique filesystem path, without creating the file Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-02-25 10:05 +0000
            Re: Make a unique filesystem path, without creating the file Chris Angelico <rosuav@gmail.com> - 2016-02-23 06:37 +1100
            Re: Make a unique filesystem path, without creating the file Steven D'Aprano <steve@pearwood.info> - 2016-02-23 11:03 +1100
              Re: Make a unique filesystem path, without creating the file Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-02-23 00:11 +0000
              Re: Make a unique filesystem path, without creating the file Paul Rubin <no.email@nospam.invalid> - 2016-02-22 18:27 -0800
                Re: Make a unique filesystem path, without creating the file Chris Angelico <rosuav@gmail.com> - 2016-02-23 13:53 +1100
                Re: Make a unique filesystem path, without creating the file Paul Rubin <no.email@nospam.invalid> - 2016-02-22 19:26 -0800
                Re: Make a unique filesystem path, without creating the file Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-02-23 08:09 +0000
                Re: Make a unique filesystem path, without creating the file Paul Rubin <no.email@nospam.invalid> - 2016-02-23 00:22 -0800
                Re: Make a unique filesystem path, without creating the file Peter Otten <__peter__@web.de> - 2016-02-23 09:40 +0100
                Re: Make a unique filesystem path, without creating the file Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-02-23 09:00 +0000
                Re: Make a unique filesystem path, without creating the file Grant Edwards <invalid@invalid.invalid> - 2016-02-23 15:14 +0000
                Re: Make a unique filesystem path, without creating the file Steven D'Aprano <steve@pearwood.info> - 2016-02-25 11:41 +1100
                Re: Make a unique filesystem path, without creating the file Random832 <random832@fastmail.com> - 2016-02-25 10:03 -0500
    Re: Make a unique filesystem path, without creating the file Steven D'Aprano <steve@pearwood.info> - 2016-02-23 11:18 +1100

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