Quote from: HZKto on December 16, 2013, 07:16:58 PM

Quote from: kjj on December 16, 2013, 07:12:41 PM

You didn't actually read this thread before posting, did you?

I did read this thread, and several old ones: https://bitcointalk.org/index.php?topic=437 , https://bitcointalk.org/index.php?topic=1647
Do you have any particular objection to discuss?

Way back on post #5 gmaxwell explains it pretty well.

Quote from: gmaxwell on May 03, 2013, 06:41:45 AM

Quote from: scintill on May 03, 2013, 06:11:50 AM

Yes, you are correct. They are there so some quantum computing farm (doesn't exist, but...) can't come out of nowhere and roll back blocks by mining a long chain from far in the past.

Thats not really what they're for though that have the effect too. Most of their usefulness is that they prevent a dos attacker from filling up bitcoin node's disk space with long runs of low difficulty blocks forked off low in the chain.

e.g. you start off with difficulty 1 blocks at block 0, now mine-able by the millions by a single asic _MAYBE_ a chain that starts off that way could eventually turn out to be the longest so absent the checkpoints a node would happily follow an endlessly long chain of them.

They also make is so that an attacker who has complete control of your network (and thus can prevent you from hearing the longest chain from the honest bitcoin network) from putting you on a fake (low difficulty) isolated chain unless they can also trick you into running replaced software. With the checkpoints such an attacker hast to have a ton of mining power in order to continue the chain.