Bitcoin Forum

I am planning this for next year. So here I'd like to gather community feedback and interest.

To enable future peer-to-peer marketplace and other advanced p2p applications I am considering adding auxiliary transaction support for a major future release of ppcoin.

Main design point is

• Each regular block is associated with an auxiliary block.
• Auxiliary blocks are not permanent. They expire after some fixed time and are garbage collected by ppcoind.
• Each auxiliary block includes a set of auxiliary transactions.
• Auxiliary transactions also has expiration and may include a (key, value) data item in each output script.
• Auxiliary transactions also pay transaction fee.
• Auxiliary transaction output cannot be spent by regular transactions.
• Auxiliary transaction may spend regular transaction output only if it's a special pay-to-auxiliary type.
• Auxiliary transaction/auxiliary block is not allowed to mint coins.

The above describes the internals of a recyclable auxiliary block chain feature.

A potential p2p marketplace software that communicates with ppcoind may implements:

• Listings are inserted into block chain as auxiliary transaction outputs.
• Listing includes seller's cryptographic identity, item description and asking price. Output has amount 0 and can be spent by anyone with another auxiliary transaction. Spender effectively claims the listing (becomes buyer) and may encrypt his/her shipping address in the auxiliary transaction output.
• Buyer now makes payment according to listing instructions.
• Users leave rating/feedback via an auxiliary transaction for the target identity.
• Manage identity/reputation/web-of-trust.
• Index listings and provide search functionality.

Note this feature is a generic design and may enable other type of p2p applications, for example, a domain name system similar to namecoin.

Comments, suggestions and feature discussions are very welcome  :)
Also looking for any community interest in designing marketplace or other softwares taking advantage of this feature.

It will be interesting to see if any developers do jump on it, as no one has yet in all this time used namecoin to do thatr, which would be perfectly feasible but just has not, for whatever reason, actually been done.

-MarkM-

Strange suggestion,

Would it be possible to build anonymous-messaging on top of an Aux Chain/Blocks?

Messages sent signed with keys, encrypted with known GPG keys; could set max lenth of X bytes, might be a nicer messaging system than say TorMail; also as they expire after X time, it would allow the "client" to if so the receipient wants, "pull" the message off of the chain.

It's probably even possible with bitcoin, but development resists this for the (valid) concern of block chain bloat. Also I think there is the issue of lack of profit motivation (no profit making model) to create the market software.

The aux block proposal addresses the block chain bloat concern, by separating the storage of auxiliary transactions and making them garbage-collectable. Also native support of multiple application-specific auxiliary transaction output is definitely some help with the application development.

As to motivation in making a peer-to-peer market software, I may consider organizing a bounty for this.

If the items you are selling are smart property they should not be garbage-collected as their whole point is the blockchain provides a permanent record of ownership. If they are not smart property you might as well put them on your website and just put directions to your website in the blockchain (thus likely use namecoin to do it).

-MarkM-

I am sure it's possible, but keep in mind data are stored on block chain for a fee (1 cent per kilobyte/message). Also there is no way for the sender or receiver to 'pull' their messages from block chain, in fact any node can choose to not to garbage collect auxiliary blocks and keep them forever. But since the message is encrypted so maybe that's not a problem.

I did not mean pull as in remove, pull in as far as make a copy for themselves, maybe in their wallet file. Any machine, aslong as you have your wallet keys, you could read your recent mail. The 1c/KB/message I think works fine. Most "messages" arnt much more than a few kb's. Obviously that could be changed in the future.

Just throwing out ideas. 

This has nothing to do with smart property you can still put them on the main block chain as you wish. This is enabling a peer-to-peer marketplace. Selling on a market with well-managed reputation system is day and night different than just 'put them on your website and just put directions to your website'. Also without the aux garbage collection feature the scalability of the block chain is greatly reduced (even ebay doesn't online all your history). Think about this, it's meant to compete with amazon/ebay etc the 1st generation internet e-commerce giants, but without central infrastructure to support it. Of course if you want to save some fees you can still put links in your listing.

Ah I see. Although the application software is meant to manage their own copies so these messages won't be stored in wallet. Yes as long as you have identity keys you can always reconstruct a copy of your messages that have not been garbage collected. This can be done by the application via commands similar to getblock/gettransaction.

I don't know if it's a good idea to reuse wallet keys for identity keys, or if there is requirements for wallet to store a different type of keys for identity.

Well just an idea of what a good aux chain for PPC might also do :) if I get enough time I might setup a MailCoin, where by mining gives you more credits to use the system, or you can buy them, it's distributed and encrypted. 

Sounds great so we can touch base again when you have more concrete plan and requirements  :)

Sounds good.  I'll start cracking together a few things.

I messaged Sunny about this a while back  :)

Would be interested to hear any more thoughts of his on this. I know he is busy strengthening the proof of stake side of the network (I believe).