1.2) Proof-of-Work of bitcoin
1). Scanning for a value that when hashed, the hash begins with
a number of zero bits.
2). increment a nonce in the block until a value is found,
that gives the block’s hash the required zero bits.
3). As later blocks are chained after it,
* the work to change the block would include redoing all the blocks
after it.
* Every block contains a hash of the previous block.
- Creating a chain of blocks from the genesis block to the current
block.
- By these properties, double-spending of bitcoins very difficult.
4) Proof-of-work difficulty is determined by a moving average targeting an average number of blocks per hour.
v* Problem of majority decision in bitcoin
1) Proof-of work is one-CPU-one-vote, not one-IP-one-vote.
2) Majority decision is represented by the longest chain.
è To modify a past block, an attacker redo the proof-of-work of
the block and all blocks after it.
è Probability of attack reduces exponentially as next blocks are
added.
* Block of bitcoin
* There are multiple valid solutions for any given block
- only one of the solutions needs to be found for the block to be solved.
* Coinbase transaction: known as a generation transaction.
- appearing the first transaction in every block.
* The number of generated Bitcoins per block: starts at 50.
- halved every 210,000 blocks (about four years).
* Bitcoin transactions are broadcast to the network,
- all peers trying to solve blocks collect the transaction records.
- add the transaction records to the block.
* The difficulty of bitcoin is automatically adjusted by the network,
- solving an average of 6 blocks per hour.
- every 2016 blocks (about two weeks).
* This increases (or decreases) the difficulty of generating blocks.
* Hash of block: SHA-256 hash of a block's header.
- between 0 ~ the maximum value of a 256-bit number.
- bitcoin uses: SHA256(SHA256(Block_Header))
* If your hash is below the target, then you win.
- If not, you increment the nonce and try again.
