[Bitcoin-development] BIP draft - Auxiliary Header Format

Tier Nolan tier.nolan at gmail.com
Mon Nov 10 11:42:17 UTC 2014

The aheaders message is required to make use of the data by SPV clients.
This could be in a separate BIP though.  I wanted to show that the merkle
path to the aux-header transaction could be efficiently encoded, but a
reference to the other BIP would be sufficient.

For the other messages, the problem is that the hash of the aux header is
part of the block, but the aux header itself is not.  That means that the
aux header has to be sent for validation of the block.

I will change it so that the entire aux-header is encoded in the block.  I
think encoding the hash in the final transaction and the full aux-header in
the 2nd last one is the best way to do it.  This has the added advantage of
reducing the changes to block data storage, since the aux-header doesn't
have to be stored separately.

On Mon, Nov 10, 2014 at 12:52 AM, Gregory Maxwell <gmaxwell at gmail.com>

> Some initial comments...
> Tying in the protocol changes is really confusing and the fact that
> they seem to be required out the gates would seemingly make this much
> harder to deploy.   Is there a need to do that? Why can't the p2p part
> be entirely separate from the comitted data?
> On Mon, Nov 10, 2014 at 12:39 AM, Tier Nolan <tier.nolan at gmail.com> wrote:
> > I made some changes to the draft.  The merkleblock now has the auxiliary
> > header information too.
> >
> > There is a tradeoff between overhead and delayed transactions.  Is 12.5%
> > transactions being delayed to the next block unacceptable?  Would adding
> > padding transactions be an improvement?
> >
> > Creating the "seed" transactions is an implementation headache.
> >
> > Each node needs to have control over an UTXO to create the final
> transaction
> > in the block that has the digest of the auxiliary header.  This means
> that
> > it is not possible to simply start a node and have it mine.  It has to
> > somehow be given the private key.  If two nodes were given the same key
> by
> > accident, then one could end up blocking the other.
> >
> > On one end of the scale is adding a transaction with a few thousand
> outputs
> > into the block chain.  The signatures for locktime restricted
> transactions
> > that spend those outputs could be hard-coded into the software.  This is
> the
> > easiest to implement, but would mean a large table of signatures.  The
> > person who generates the signature list would have to be trusted not to
> > spend the outputs early.
> >
> > The other end of the scale means that mining nodes need to include a
> wallets
> > to manage their UTXO entry.  Miners can split a zero value output into
> lots
> > of outputs, if they wish.
> >
> > A middle ground would be for nodes to be able to detect the special
> > transactions and use them.  A server could send out timelocked
> transactions
> > that pay to a particular address but the transaction would be timelocked.
> > The private key for the output would be known.  However, miners who mine
> > version 2 blocks wouldn't be able to spend them early.
> >
> >
> > On Sat, Nov 8, 2014 at 11:45 PM, Tier Nolan <tier.nolan at gmail.com>
> wrote:
> >>
> >> I created a draft BIP detailing a way to add auxiliary headers to
> Bitcoin
> >> in a bandwidth efficient way.  The overhead per auxiliary header is only
> >> around 104 bytes per header.  This is much smaller than would be
> required by
> >> embedding the hash of the header in the coinbase of the block.
> >>
> >> It is a soft fork and it uses the last transaction in the block to store
> >> the hash of the auxiliary header.
> >>
> >> It makes use of the fact that the last transaction in the block has a
> much
> >> less complex Merkle branch than the other transactions.
> >>
> >>
> https://github.com/TierNolan/bips/blob/aux_header/bip-aux-header.mediawiki
> >>
> >
> >
> >
> ------------------------------------------------------------------------------
> >
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> > Bitcoin-development at lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/bitcoin-development
> >
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