I was looking into how blockchain mining works and I've figured out that the nonce is a key part of the block header that helps identify blocks. From what I gather, the nonce is important for getting a hash that fits the network's difficulty level.
I'm curious, though. Is the nonce actually part of the hashing process when trying to hit that difficulty target, or is it only used once a miner successfully adds a block to the chain? Also, what role does the nonce play in the mining process and when it comes to verifying blocks?
A nonce is a number that miners combine with block data and turn into a hash. They repeatedly adjust this number until they find a hash that meets a certain difficulty level. A basic example would be a hash that begins with a specific number of zeros, known as "proof of work" (PoW).
The first miner to find a hash meeting the required difficulty is rewarded with freshly minted Bitcoins and any transaction fees associated with the block.
This hash must be included in the next block, ensuring that a block can never be mined prematurely.
The nonce does not identify the block.
The purpose of the nonce is to be an inexpensive way to change the block hash. Once everything else in the block is set up, the miner will quickly hash the block header with all of the 4 billion possible nonce values until a valid hash is found. If a valid hash is not found, the miner will make a change to the block and try again. The same thing is done in a limited way with the timestamp.
We "identify" blocks with their hashes (block ID like transaction ID) not their header details, specially not nonce that is a random meaningless variable. The 4-byte nonce value is an inseparable part of the header so like other parts it is "crucial" but not special.
We have to go back to understand what Proof of Work algorithm does.
In PoW the goal is to introduce a "work" that the "worker" has to perform over and over until they find a "correct result".
In Bitcoin, that work is computing hash of the block header. Hash is used because its result is unpredictable and the worker has to perform the actual work to know the result (has to compute the hash of all permutations to get the digest).
In each step, the miner has to make a small change (flip a bit) to get an entirely different result. But the block header contains values that:
- can not be changed at all like 32-byte previous block header hash
- some values that have a limit on how much they can change like version and time
- some values that cost more to change like the merkle root hash that requires changing the txs inside the block and re-computing the merke root again
So an extra value is added to the header that is meaningless and can be freely changed without affecting anything. That is the nonce. So the miner can compute 0xFFFFFFFF (4,294,967,295) hashes very easily before they have to change something else like the merkle root hash.
Noted
In a bid to understand this better I went back to see how this is been implemented in real sense. Writing a simple script expanded on this. My take home from your explanation is that the nonce provides a means to alter the block hash efficiently. That means if a miner needs to find a hash that starts with "0000". The hash function processes the block header, and the miner starts with a nonce of 0. And assuming they get a hash like a1b2c3... that doesnt meet the requirement. Incrementing the nonce to 1 might yield a different hash, and they continue this process until they find the solution, say, 0000abcd....
I wanted to have a feel of this so I had to research on how it works in real sense and writing a simple script expanded the concept better. I wrote two functions one to attempt a fake mining process and another to create a block header
I used a difficulty of 4 and when i called my function it generated this nonce 45401 and a hash of 00004e3e53c08848a83a6d0f1d4612bcd7b62c2578c5e0f21f8e38c196000b76. this just defines how hard it is to find a hash that meets the criteria
I proceeded to finding the block header which lead to writing the second function that adds the The version, the previous hash, the markle root, timestamp, bits and the nonce.
It is making more sense to me now.
000000010000000000000000000e1f1c8b70d60e1b6b021c6e2f0f6c1c9b8b77b2b1d1db4c6c3d8 d60a1c7b1f1b2f4c3b3e1e1f4f4c3b3b1b2b2c7b11c1c7b2d3c4d5e6173486627817048edf45401 ..
I am still learning and still open to more corrections
If you are just experimenting to see how the loop works and get a vague feeling of PoW then this could be fine but you should know that the check you are performing here is wrong.
In Proof of Work we actually convert the hash to an integer in little endian order and see if it is smaller than or equal to the target (also converted to an integer).
You can read this whole topic about difficulty and my comment about why counting zeros is wrong. https://bitcointalk.org/index.php?topic=5522336.msg64835659#msg64835659