How Blockchain technology verifies proof of work

manpreet Best Answer 2 years ago

I am learning Blockchain with some online examples. I have this high level code where I am creating a new Block with previous hash and then am adding a transaction to it and then generating a difficult hash (with 8 leading zeros) of the block

 Block block1 = new Block(previousHash);
 block1.addTransaction(new SomeTransaction());
 block1.mineBlock(difficulty);
 blockchain.add(block1);


public void mineBlock(int difficulty) {
    String target = StringUtil.getDificultyString(difficulty); //Create a string with difficulty * "0"
    while(!hash.substring( 0, difficulty).equals(target)) {
        nonce ++;
        hash = calculateHash();
    }
    System.out.println("Block Mined!!! : " + hash);
}

This works well. But I have a question that how this proof of work is verified before adding a block to blockchain.

i.e. Suppose have generated a hash with 8 leading zeros

000000005ed2248f32d7f2509e6291a998a6119b96b1227d27fe03cf21b8c908

How will blockchain ensure that this hash is actually a valid hash and not just a random sequence of characters with 8 leading zeros?

manpreet 2 years ago

It's very easy to compute the hash based on the previous block and the nonce you discovered. There is no need for a loop, just one hash computation, which is fast. So when you add the new block to the chain, you also publish the nonce, and they just compute the hash -- that's the proof of work.