To put this discussion in the right place ...
The description above by DeathAndTaxes is completely clueless (you missed completely what "create hash" is)
Funny you say then then link to a document which says the same thing.
This is of course a guess - but it would appear that namecoin is putting extra information in the coinbase - i.e. increasing the bitcoin block size.
(I'm guessing this due to a discussion with luke-jr)
No need to guess. That isn't how it works at all. Funny you "know" what I said was wrong yet you haven't even figured out how it works (still making wrong guesses).
Edit: Well I guess I now have the link to get the official code at least ... from DavinciJ15 :
http://dot-bit.org/Merged_Mining(can't remember where I got it last time I compiled and ran it)
Lets take a look at that.
"Merged mining works like this, you have two totally separate block chains, they are not related in any way nor does either contain any data from the other. When you mine you generate hashes that may be the solution to the current block, this is very very improbable per hash, its like a lottery where everyone generates tickets until someone finds the winning one. Normally you make tickets and check them against the Bitcoin block chain to see if they are the solution. With merged mining you create a ticket and check it against both the Bitcoin block chain and the Namecoin block chain, Bitcoin and Namecoin know nothing about each other, they are two totally different lotteries with different winning numbers, you just sent a copy of your ticket to both. Since you are sending the same ticket to two lotteries you increase your chances of winning one or the other. No Bitcoin data goes into Namecoin no Namecoin data into Bitcoin they remain totally separate, you simply run both the Namecoin and Bitcoin clients on the same machine and submit hashes to both networks, if your hash is the solution to the Namecoin block you get Namecoins if you hash is the solution to the Bitcoin block you get Bitcoins, its exactly like if you where mining on just one network, except you submit the same work twice."
Single hash checked against both bitcoin and namecoin targets. Hmm sounds exactly like my "wrong" answer above.
I didn't link to that document, I referred to where I could gain the source.
That document is wrong.As I said you completely missed what "create hash" is.
"create hash" is hashing the contents of the block that goes into the block chain and then checking if it is under the difficulty requirement.
If both are true, you then have a block.
Since you are hashing the contents of the block, you cannot even compare that to some other different block.
It's not possible.
What is possible, is to add extra data to the block, that some other block chain can check against and decide it will allow it to be a block.
The hash of the bitcoin block hashes the following information:
version
previous_hash
time
difficulty
nonce
the miner's extranonce
the transactions in the block (this includes the generation block which has the coinbase)
i.e. the whole block
The above information is mandatory for the block chain to be secure.
It ensures that no one can change the block chain somewhere in the middle.
Thus the bitcoin hash is the hash of the complete bitcoin block contents.
It is not the hash of ANYTHING more or less.
For a hash for namecoin to be securely usable in both bitcoin and namecoin, the bitcoin block would have to contain something extra added that namecoin can use.
If this were not true, then namecoin would have to rely completely on the contents of the bitcoin block chain to secure itself i.e. namecoin would become dependent on having a copy of the whole bitcoin block chain to be able work.
P.S. I still haven't read the namecoin code yet