Bitcoin Forum

Bitcoin => Development & Technical Discussion => Topic started by: s.matthew.english on October 26, 2016, 03:15:15 PM



Title: lower bound of block size towards increased speed of propagation
Post by: s.matthew.english on October 26, 2016, 03:15:15 PM
As far as I know there is an upper bound of a block, which is one megabyte, is there a lower bound?

It was in terms of a race condition that I was considering this.

Imagine you make a double spend and then you try to propagate a block that contains only your second transaction. If so it would be much smaller, ipso facto easier to propagate around the network and get validated by nodes, isn't that right?

Maybe someone in the mean time would find a valid block for one containing many transactions, in which case it would be longer than yours, and maybe other miners would extend that- but maybe not.

Does anyone want to try this out on the testnet with me?

PS. I'm posting this here because I got no response on stackexchange


Title: Re: lower bound of block size towards increased speed of propagation
Post by: DannyHamilton on October 26, 2016, 04:48:17 PM
As far as I know there is an upper bound of a block, which is one megabyte, is there a lower bound?

Yes.

To be valid, a block MUST have an 80 byte block header and a generation transaction.

I'm not certain about the minimum size of the generation transaction, but I think it's about 22 bytes or so?  That would make the minimum block size about 102 bytes.

If you wanted to include a transaction of your own in that block, you'd need to add in the size of your transaction as well.

Imagine you make a double spend and then you try to propagate a block that contains only your second transaction. If so it would be much smaller, ipso facto easier to propagate around the network and get validated by nodes, isn't that right?

Slightly, but you'd still have to actually mine the block which will take much longer than the propagation time (depending on your hash power).