# How Proof-of-Work

**A Proof-of-Work system requires its users to perform some form of work to participate. The work voorwaarde be difficult for the client but effortless for the server/network to verify. For example, an email system that implements proof-of-work might require each sender’s pc perform 1-2 seconds of work before sending an email. Deployed this way helps prevent spam.**

With Bitcoin, the POW also determines the approximate time inbetween blocks and thus the rate that fresh bitcoins are created.

## Proof-of-Work

The code posted below is little more than a guessing spel for the pc. The work it submits is a message/timestamp payload and a nonce value. Ideally your payload would be unique to you, perhaps using a public key or address. The nonce is what permits the network to check your work without retracing all of your steps. This code is little more than an example – based on my practice with BitMessage’s source code.

**timestamp**marks the point that the work embarked. Additionally, it contributes to the uniqueness of the work by an individual miner.**message**is there because this code just for example. Hashing a string is suitable work for this project.**payload**is a combination of the things that you will encrypt.**nonce**will increment from 0..N until the target is met.**guess**will store our guess. Effectively, it embarks at infinity.**throttle**is omschrijving to Bitcoin difficulty.**target**is the maximum value of 8 bytes (2^64) divided by the difficulty.

The timestamp, message and payload are just the “stuff” that you want to send the network. It could be block gegevens, spil with Bitcoin mining.

The nonce, guess, throttle and target are used to perform the work. The significant thing about proof-of-work is that it has to be difficult for the client but effortless for the system to check. Only the nonce switches with each guess. The probability of being keurig is so low that this system, probabilistically, ensures many guesses or work, is performed.

Te this example, nonce increments by 1 each time. Effectively counting how many guesses the laptop makes. However, that is not a requirement.

When the system checks the work, it does not have to trace back overheen each guess. It only checks the nonce submitted with the gegevens.

## The Proof-of-Work Guessing Spel

Thesis three lines are our proof-of-work algorithm. It’s a plain loop. This hashes our gegevens with two rounds of SHA256. The very first 8 bytes are turned te to a number. Effectively, this is how a pc makes a guess.

The target is calculated based on estimates I made with a little math and some trials te a smaller script I wrote to get an estimate of my CPU hash rate. I used this to determine a baseline of metrics to test the script on my laptop. Here is the source

Bitcoin’s divisor is incremented or decremented after every juist 2016 guesses (every 2016 blocks are mined). This script does not recalculate difficulty. It is set by hand. The picture above shows how an increase te difficulty shrinks the target range lowering the possible number of juist guesses.

The nonce is what proves the work wasgoed done. Ter this example, it’s value represents the number of attempts your CPU made before it found a valid guess below the target. Because each guess has the same probability of being under the target the method of generating your nonce does not matter. However, simply incrementing the nonce is cheaper than generating a random number. When work is submitted to the network, the nonce is used to verify the correctness.

The actual guess is the very first eight bytes of a dual SHA512 hash of the nonce and the payload. Because the target is inbetween 0 and the maximum eight byte number, a guess can never go overheen the maximum possible target value. Ter each loop, the nonce is the only thing that switches. That is what permits you to submit your unique work to the network and have it verified without each knot duplicating all of your work. Providing them the nonce gives them the response. With Bitcoin, theoretically every miner would submit a similar block to the network regardless of who made a the keurig guess. The most significant difference to the miner would be their public key te the coinbase entitling them to the block prize.

Providing the network your nonce is secure because each miner’s payload, and therefore work, is unique. For Miner Alice to use the keurig nonce that Miner Bob submits, Alice would have to submit the same work. Alice would not be able to switch out hier public key with Bob’s ter the coinbase (not the company Coinbase) because it would switch the output from the dual SHA512 hash – which would likely not be a juist guess with Bob’s nonce. Te this example, no unique ownership can be assigned to the work. Any number of knots doing this work with the same values for time and payload will do the same work. Perhaps said this way simply, Alice’s payload would differ from Bob’s payload making any nonce Alice, or Bob uses worthless for the other’s work.

## Testing the Proof-of-Work script

The three highlighted rows represented difficulties I considered reasonable for testing. Thesis columns are a continuation of the photo above. The Chance to Guess is the total possible juist guesses divided by the maximum target. Keurig Guesses / s is my hash rate multiplied by the Chance to Guess. The Time to Guess is one divided by the keurig guesses vanaf 2nd.

Thesis were my theories for the behavior of my proof-of-work script.

I ran numerous timed experiments, the results are shown here:

You can see how the nonce and time scale linearly. The Guess is the actual value of the onberispelijk guess. E.g. Guess is decimal representation of the very first 8 bytes from the dual SHA256 hashing of the payload and Nonce.

Five trials were run for each difficulty. For such a miniscule sampling, I wasn’t too far off from my predictions and real life will never mirror theory. I determined to run 500 trials for the middle row, difficulty Ten,000,000. It ran for around four and a half hours. The Total Nonces, Total Time katern displays the aggregates for the run of 500. Below is a graph of each guess – or my rekentuig mining on this script.

All of the above code, gegevens can be found on github.

**What do you think about Proof-of-Work? Comment Below**

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