[Bitcoin-development] BIP draft - Auxiliary Header Format

Tier Nolan tier.nolan at gmail.com
Mon Nov 10 00:39:20 UTC 2014

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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