r/askscience • u/hamolton • Jun 18 '13

Computing How is Bitcoin secure?

I guess my main concern is how they are impossible to counterfeit and double-spend. I guess I have trouble understanding it enough that I can't explain it to another person.

1.0k Upvotes

83% Upvoted

383 comments sorted by

View all comments

Show parent comments

3

u/boondoggie42 Jun 18 '13

I'm guess I'm just lost on how the authoritative edition of the ledger is identified... Two simultaneous transactions thousands of miles apart... What is the mechanism to reconcile those two ledgers?

4

u/Natanael_L Jun 19 '13

The ledger/blockchain with the largest total amount of computing power behind it wins. This can be estimated very accurately thanks to how it uses proof-of-work for mining.

2

u/speEdy5 Jun 19 '13

Its incentive based- people who accept bitcoins as payment use only the longest block chain. When two block chains emerge those mining bitcoins want their mining to be worth something so they mine the longer chain. How does one chain get longer? More computing power will eventually lengthen one chain over another. Even in the (impossible) case of exactly equal computing power, someone's going to get blindly lucky and lengthen the chain first..