[148599] in cryptography@c2.net mail archive
Re: [Cryptography] BitCoin Question - This may not be the best
daemon@ATHENA.MIT.EDU (Steve Weis)
Sun Dec 22 21:34:01 2013
X-Original-To: cryptography@metzdowd.com
In-Reply-To: <CAB==r-DOR=9kTLN8F8F5DG_1XbQKopmYOy170=NGwssTuDJPpw@mail.gmail.com>
From: Steve Weis <steveweis@gmail.com>
Date: Sun, 22 Dec 2013 17:59:36 -0800
To: Robert Christian <robertjchristian@gmail.com>
Cc: cryptography <cryptography@metzdowd.com>
Errors-To: cryptography-bounces+crypto.discuss=bloom-picayune.mit.edu@metzdowd.com
On Sun, Dec 22, 2013 at 4:30 PM, Robert Christian
<robertjchristian@gmail.com> wrote:
> 2) I am pointing out that addresses are finite, and 34 chars long... They
> can only be upper or lower case, or 0..9. So at the end of the day, after
> all the fancy stuff, the number of all possible bitcoin addresses is
> (26*2+10)^34 possible unique ids.
>
> So the number of possible unique addresses is actually relatively smalll.
> Right?
The address has 20-bytes of hash, a network ID byte prefix, and a
4-byte checksum. So, there are 2^160 possible unique addresses. This
is converted into a 34 character base-58 string.
You do bring up one point that many key pairs will collide for a
particular address. That's why the hash function must be assumed to be
collision resistant.
As for when we might see collisions, with a birthday attack you'd
expect there to be a 50% chance of some collision existing when there
are roughly 2^80 addresses.
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