Bitcoin Forum

Hello,

I'm having a hard time trying to find what is exactly being hashed ( plus the nonce ) to find the string with enough 0's.
I've tried the previous tx hash, the current and previous Merkle root, but no luck.

Does anyone know?

Thanks

A little intro into PoW can be found in the wiki [1], more can be found in the whitepaper[2] and the dev guide [3].
In short: you hash the header [4] which includes the nounce as well as the merkle root hash (thus a different set of transactions result in a different blockhash even if the nonce is the same) the previous blocks hash etc. (see [4] for details)


[1] https://en.bitcoin.it/wiki/Proof_of_work
[2] https://bitcoin.org/bitcoin.pdf   -  chapter 4
[3] https://bitcoin.org/en/developer-guide#proof-of-work
[4] https://bitcoin.org/en/developer-reference#block-headers

Thanks for the reply.
There is one piece of information from the block header I don't know where to get it from. It says the target threshold is needed, but does not say what it is. Is it the current difficulty?

The block header will be exactly 80 bytes in length.
You need to hash the header in binary format, not text format.

Yes, but to build the header I need to know the nBits and I don't know where to find that value.

It is a representation of the difficulty in a particular format.  You can look at the code to find out, or probably there are also guides/docs somewhere about it.

Ok, thanks I'll try to write a tutorial with the information given here.