From: Gregory Maxwell <greg@xiph•org>
To: Peter R <peter_r@gmx•com>
Cc: Bitcoin Development Discussion <bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Compact Block Relay BIP
Date: Tue, 10 May 2016 02:12:03 +0000 [thread overview]
Message-ID: <CAAS2fgR8j5QJkVb2rEfpi27OvN4gVw2ROaehLRvsojQd7yrpXg@mail.gmail.com> (raw)
In-Reply-To: <5C2809F9-286D-49E4-89DB-7109B73F6076@gmx.com>
On Mon, May 9, 2016 at 11:37 PM, Peter R <peter_r@gmx•com> wrote:
> It is a standard result that there are
> m! / [n! (m-n)!]
> ways of picking n numbers from a set of m numbers, so there are
>
> (2^32)! / [2! (2^32 - 2)!] ~ 2^63
> possible pairs in a set of 2^32 transactions. So wouldn’t you have to perform approximately 2^63 comparisons in order to identify which pair of transactions are the two that collide?
>
> Perhaps I made an error or there is a faster way to scan your set to find the collision. Happy to be corrected…
$ echo -n Perhaps. 00000000f2736d91 |sha256sum
359dfa6d4c2eb2ac81535392d68af4b5e1cb6d9c6321e8f111d3244329b6a4d8
$ echo -n Perhaps. 0000000011ac0388 |sha256sum
359dfa6d4c2eb2ac44d54d0ceeb2212500cb34617b9360695432f6c0fde9b006
Try search term "collision", or there may be an undergrad Data
structures and algorithms coarse online-- you want something covering
"cycle finding".
(Though even ignoring efficient cycle finding, your factorial argument
doesn't hold... you can simply sort the data... Search term
"quicksort" for a relevant algorithm).
next prev parent reply other threads:[~2016-05-10 2:12 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-02 22:13 Matt Corallo
2016-05-03 5:02 ` Gregory Maxwell
2016-05-06 3:09 ` Matt Corallo
2016-05-08 0:40 ` Johnathan Corgan
2016-05-08 3:24 ` Matt Corallo
2016-05-09 9:35 ` Tom Zander
2016-05-09 10:43 ` Gregory Maxwell
2016-05-09 11:32 ` Tom
[not found] ` <CAAS2fgR01=SfpAdHhFd_DFa9VNiL=e1g4FiguVRywVVSqFe9rA@mail.gmail.com>
2016-05-09 12:12 ` [bitcoin-dev] Fwd: " Gregory Maxwell
2016-05-09 23:37 ` [bitcoin-dev] " Peter R
2016-05-10 1:42 ` Peter R
2016-05-10 2:12 ` Gregory Maxwell [this message]
2016-05-09 13:40 ` Peter Todd
2016-05-09 13:57 ` Tom
2016-05-09 14:04 ` Bryan Bishop
2016-05-09 17:06 ` Pieter Wuille
2016-05-09 18:34 ` Peter R
2016-05-10 5:28 ` Rusty Russell
2016-05-10 10:07 ` Gregory Maxwell
2016-05-10 21:23 ` Rusty Russell
2016-05-11 1:12 ` Matt Corallo
2016-05-18 1:49 ` Matt Corallo
2016-05-08 10:25 Nicolas Dorier
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