Quote from: Shadow Wizard on July 07, 2011, 08:48:05 PM

Quote from: jg on July 07, 2011, 07:37:20 PM

Also, solving a block by hand means that you need to calculate sha256(sha256(block of transactions + nonce)) where the hash conforms to the current difficulty... Keep in mind that all miners (combined) are currently trying 11197.84 GHashes/sec. It would take longer than the rest of your life to complete by hand.

sha256(sha256(block of transactions + nonce))
Can you explain exactly what that is,or where to go to find out.
And as far as longer then the rest of my life, I am quite aware. It is just I find knowing how to manually do it is understanding it.

SHA256 is a hash (or compression) function (see here).
The transactions are people sending btc to each other (signed with their private key).
A nonce is basically a random value.

Basically, a block contains a list of transactions plus a nonce. The SHA256 function is calculated twice. Once on the list of transactions + nonce and once again on the output of the first SHA hash.

The difficulty requirement is that there are a certain number of leading zeros in the output of the SHA function. Miners basically take a list of transactions, and do the above calculations, only changing the nonce each time. Eventually, someone will get lucky and find the correct nonce so that the output of the chained sha256 functions has enough leading zeros. Once that happens, that block is considered solved and work begins on the next block.