Bitcoin mining algorithm name

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Retrieved 9 December Archived from the original on 23 October Archived from the original on 9 March Retrieved 9 March Principles, Trends, Opportunities, and Risks". Any block whose header does not produce a hash that is less than the target value will be rejected by the network. The target value is adjusted by the protocol every two weeks to try to maintain an average block time of 10 minutes.

This is where the nonce comes in. The nonce is simply a random number that is added to the block header for no other reason than to give us something to increment in an attempt to produce a valid hash. If your first attempt at hashing the header produces an invalid hash, you just add one to the nonce and rehash the header then check to see if that hash is valid.

This is Bitcoin mining in a nutshell. This is essentially what Bitcoin mining is, just rehashing the block header, over, and over, and over, and over, until one miner in the network eventually produces a valid hash. When he does, he relays the block to the rest of the network. If so, they add the block to their local copy of the block chain and move on to finding the next block.

However, the more hashes that you can perform per second, the greater the probability that you will mine a block and earn the block reward.

At present, the total hashing power in the network is about terrahashs per second and closing in on one petahash per second. Because each miner is sending these 25 bitcoins to his own address, the first transaction in each block will differ from miner to miner.

Now remember the properties of a cryptographic hash function? If an input changes even in the slightest, the entire output changes. Since the hash of the coinbase transaction at the base of the hash tree is different for each miner, the entire hash tree including the Merkle root will be different for each miner. That means the nonce that is needed to produce a valid block will also be different for each miner. This is the reason why the Merkle tree is employed after all.

Any change to a single transaction will cause an avalanche up the hash tree that will ultimately cause the hash of the block to change.

If an attacker wants to alter or remove a transaction that is already in the block chain, the alteration will cause the hash of the transaction to change and spark off changes all the way up the hash tree to the Merkle Root. Given the probabilities, it is unlikely a header with the new Merkle Root will produce a valid hash the proof of work. Hence, the attacker will need to rehash the entire block header and spend a ton of time finding the correct nonce.

But suppose he does this, can he just relay his fraudulent block to the network and hope that miners will replace the old block with his new one or, more realistically, that new users will download his fraudulent block? The reason is because the hash of each block is included in the header of the next block. If the attacker rehashes block number , this will cause the header of block to change, requiring that block to be rehashed as well.

A change to the hash of block will cause the header of block to change and so on all the way through the block chain. Any attempt to alter a transaction already in the block chain requires not only the rehashing of the block containing the transaction, but all other subsequent blocks as well. Depending on how deep in the chain the transaction is, it could take a single attacker weeks, months, or years, to rehash the rest of the block chain.

The only exception to the above rule is if the attacker simply gets lucky. As we noted, it takes the entire network an average of 10 minutes to find a valid block. The deeper a transaction is in the block chain, however, the more times in row the attacker would need to get lucky and mine a block before the rest of the network to extend his chain longer than the main chain.

Which is usually why it is recommended that if you are selling something expensive, you should wait until your transaction is six blocks deep six confirmations in Bitcoin lingo before actually handing over the merchandise. This post got long in a hurry. Hope you enjoyed these posts and I hope you learned something.

I found your post comments while searching Google. It is very relevant information. Regularly I do not make posts on blogs, but I have to say that this posting really forced me to do so.

Really fantastic and I will be coming back for more information at your site and revisit it! I still have one question though: Smart Contracts Great Wall of Numbers.

CPU mining quickly gave way to GPU mining graphics processing units which proved much more efficient at calculating hash functions. Basically, these are purpose built computer chips that are designed to perform SHA calculations and do nothing else. At present, the total hashing power in the network is about terrahashs per second and closing in on one petahash per second. Because each miner is sending these 25 bitcoins to his own address, the first transaction in each block will differ from miner to miner.

Any change to a single transaction will cause an avalanche up the hash tree that will ultimately cause the hash of the block to change. If an attacker wants to alter or remove a transaction that is already in the block chain, the alteration will cause the hash of the transaction to change and spark off changes all the way up the hash tree to the Merkle Root.

Given the probabilities, it is unlikely a header with the new Merkle Root will produce a valid hash the proof of work.

Hence, the attacker will need to rehash the entire block header and spend a ton of time finding the correct nonce. But suppose he does this, can he just relay his fraudulent block to the network and hope that miners will replace the old block with his new one or, more realistically, that new users will download his fraudulent block?

The reason is because the hash of each block is included in the header of the next block. If the attacker rehashes block number , this will cause the header of block to change, requiring that block to be rehashed as well.

Depending on how deep in the chain the transaction is, it could take a single attacker weeks, months, or years, to rehash the rest of the block chain. The only exception to the above rule is if the attacker simply gets lucky. As we noted, it takes the entire network an average of 10 minutes to find a valid block. The deeper a transaction is in the block chain, however, the more times in row the attacker would need to get lucky and mine a block before the rest of the network to extend his chain longer than the main chain.

From a probability standpoint, the chances of such an attack succeeding decrease exponentially with each subsequent block. In the original white paper Satoshi Nakamoto calculated the probabilities that an attacker could get lucky and pull off a double spend. In the following table q is the percentage of the network controlled by the attacker, P is the probability an attacker could get lucky and override z number of blocks. Which is usually why it is recommended that if you are selling something expensive, you should wait until your transaction is six blocks deep six confirmations in Bitcoin lingo before actually handing over the merchandise.

This post got long in a hurry. Hope you enjoyed these posts and I hope you learned something. I found your post comments while searching Google. It is very relevant information. Regularly I do not make posts on blogs, but I have to say that this posting really forced me to do so. Really fantastic and I will be coming back for more information at your site and revisit it!

I still have one question though: Smart Contracts Great Wall of Numbers. Part 2 — Mechanics … Bitcoin. For the hash chaining, does it mean if somebody get one valid hash, I need to update and download it and re-calculate based on his block?