ToGETHER1: bitcoin

https://en.bitcoin.it/wiki/Protocol_specification#block

Merkle tree is to make sure that data blocks (transactions) received

from other peers in a peer-to-peer network are received undamaged and unaltered,

and even to check that the other peers do not lie and send fake blocks.

Merkle tree can be used to verify any kind of data stored.

This is example of how to get the hash of block header in bitcoin.

* Calculation of the hash of block header

Most of block header will be the same for all users.

There might be some minor variation in the timestamps.

The nonce will usually be different, but it increases in a strictly linear way.

"Nonce" starts at 0 and is incremented for each hash.

Whenever Nonce overflows (which it does frequently),

the extraNonce portion of the generation transaction is incremented,

which changes the Merkle root.

Given block header, people generate the exact same sequence of hashes

as each other and the fastest CPU would almost always win.

However, it is (nearly) impossible for two people to have the same Merkle root

because the first transaction in your block is a generation "sent"

to one of your unique Bitcoin addresses.

Thus, your block is different from everyone else's blocks.

https://en.bitcoin.it/wiki/Block_hashing_algorithm

The method of obtainig the difficulty of bitcoin.

* Difficulty: a measure of how difficult it is to find a new block.

- changed by every 2016 blocks.

- difficulty = maximum_target / current_target.

- maximum target in bitcoin is constant.

==> 0x00000000FFFF0000000000000000000000000000000000000000000000000000

- lower current target makes Bitcoin generation more difficult.

the maximum target is the lowest possible difficulty.

* Difficulty 1 is defined as 0x1d00ffff,

- maximum target : 0x00ffff * 2**(8*(0x1d - 3))

= 0x00000000FFFF0000000000000000000000000000000000000000000000000000

* The maximum difficulty: roughly maximum_target / 1, (about 2^224)

2014년 1월 24일 금요일