On 2016-02-23, Chris Angelico <ros...@gmail.com> wrote: > On Tue, Feb 23, 2016 at 11:26 AM, Jon Ribbens ><jon+use...@unequivocal.co.uk> wrote: >> On 2016-02-23, Chris Angelico <ros...@gmail.com> wrote: >>> On Tue, Feb 23, 2016 at 11:08 AM, Jon Ribbens >>><jon+use...@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. -- https://mail.python.org/mailman/listinfo/python-list
