This is exactly the case.  I'm implementing an altcoin myself, and the major requirements of this bounty (length limited blockchain, recovery of lost coins, reasonably trustable zero-confirm transactions)  closely resemble some of the novel features I had already intended to do anyway.   So I was already planning to write some very similar code.  If someone else is willing to pay a bounty for this particular set of requirements, and afterwards I still have rights to open-source, modify, and use the code produced, then doing this gets me about 80% of the way to the versions of these features I want to implement for my own system. 

It's earlier in my dev plan than I had intended to do it, but the set of requirements here apply to a transaction model much simpler than mine (I'm going to be using pay-to-script-hash and several different families of addresses with different properties) so it can exist independently of the complications I'll need to integrate it with.  Implementing this version will be easier and cleaner than what's going to eventually wind up in my code, but it'll still be a very good starting point for me.

FWIW, I think having the miner detect double spends is far too late for zero-confirm transactions.   It ought to be possible to repudiate a doubly-spent transaction within ten seconds, or the capability becomes one that won't be practical to use (in situations like checkout lines with people waiting behind you, or vending machines where you're just grabbing something on your way somewhere and don't have extra minutes, etc).  It doesn't matter if the double spend is "punished" or not; the merchant is still left holding the bag and that's _not_ okay!  I say ten seconds because that's roughly the amount of time it takes for a transaction to propagate across the Bitcoin network to 90% or more of the nodes and it'll only take a couple of seconds for an online merchant to check with ten or so clients at least a few of which are likely to have heard of the other transaction.

@Bitfreak!

Another requirements question.  When you say you'd like "recovery of lost coins" do you mean "recovery of coins sent to addresses/keys whose corresponding private keys have not been used in X time"?  Or do you mean "recovery of coins in addresses/keys that have not been used in *ANY* transaction (ie, neither the private key nor the public key has been used) in X time"?

I ask because it's possible that Alice lost the private key to one of her addresses many years ago, but Bob just sent coins to that address using the public key just last week.  Are the  coins Bob sent to be considered "lost" because the only key that could possibly spend them hasn't been used for many years, or are those coins (and all other coins in Alice's old account) to be considered "live" because the public key to that account was used only last week?

If we go with the first option, then once Alice's old account has been "recovered", as long as she doesn't reactivate it by using the private key that we assumed was lost, any coins sent to that address may be recovered immediately, even in the very same block as the tx that sends them.  

The first option seems more sensible to me, because the only idea that causes "recovery" to make any sense is the presumption that the private key to the address has been lost. Coins recently sent to that address do not indicate that it has been found.  

But the second option is more sensible in terms of orderly data structures.  If it's the private key only then we need to keep track of the last time each account was decremented, but we may never completely delete an account from our account lookup because if the account is "dead" it remains "dead" until the private key is used, and any amounts sent to it may be recovered immediately.  If it's both private *and* public key, then we must remember the last time the balance changed in either direction, but we can delete accounts completely when they reach zero, because the effect is the same if a new spend "creates a new account" as if a new spend is directed to an account that has been "recovered".

@Bitfreak!

I'm going to take a run at this, but I want to be sure I've got the requirements right first.

When you say on the wiki page describing the Account Tree that it should be easy to reference an account by "offset and address" I'm guessing that by "address" you mean the key needed to spend to that account, but what do you mean by "offset?"

It wouldn't be hard at all to make it easy to reference an account by address alone.  That would make it equally simple to just ignore some extra data called an "offset" as being something I don't really need to find the account -- unless you mean that you also want to be able to look it up by offset alone, without needing the address for this other kind of search?

There is a bit of problem with the mini-blockchain idea as presented here. 

A blockchain is secured by the work of finding preimages for hashes.  That's what you need to do in order to build a blockchain from least recent to most recent.  However, going the other way, you just need to start with the 'preimage' you want, plug in some arbitrarily chosen nonce, and run the hash function once.   So you could fabricate a supposed 'recent' block and then, with very little effort, construct a fake chain that leads back from it -- to the full length of your mini-blockchain.

So here is the issue.  An attacker can present hundreds of bogus mini-blockchains per second and the client has to figure out which one is real.  In the absence of a way to check things back to the Genesis Block, that's difficult.

I'm not saying the problem isn't solvable.  It's just kinda non-obvious.  One thing you need to do is to make sure it's more computationally expensive to create new blocks backward than it is forward.

An arrangement like that, if it allows for some flexibility between the hexagons, could grow much larger than any rigid ship and still be able to handle very long waves out on the ocean.  It is effectively an articulated structure, which puts it light years ahead of, say, Freedom Ship in terms of practicality and ability to exist.  And leaving space between the hexes allows boats to get through, so rowboats and little sailboats could be used effectively like bikes.  (and of course motorboats would be the SUVs of the system... ).  So you'd want flexible standoffs between hexes. If you put them above the water, they'd also probably serve as bridges as well for foot, bicycle, and scooter traffic, and would have to be high enough that reasonable-size sailboats could get under them.

One thing I notice about the float city above is that it has a lot of differential loading.  Some of those hexes will need to be awfully deep, and ballasted at the lower ends, in order to support the large buildings on top of them, while those that just support a cottage and a garden can be effectively flat bottomed and quite shallow. The very deep hexes can work a lot like "sea spars" in that they can resist large waves without being capsized or necessarily having large vertical movements.  They'd be a hell of a lot harder for a violent wave to flip over or push around, for example.  So your best arrangement for a city like that, in order to withstand hurricanes etc, would be to have the "deep" hexes (and multi-hex platforms) with the big buildings on the outer edge of the city, protecting the interior, while the regular 'flat' hexes that support just a cottage and a garden should be on the interior -- effectively the reverse of the way it's pictured above.  This would also be more convenient for the heavy industries, fish packers, shipping centers, malls, and factories etc that the larger buildings likely contain, because it would give them access to the edge of the raft where larger ships for ocean traffic, and medium-size boats that would serve as trucks to take loads to other businesses around the edges of the raft, could be loaded and unloaded. 

You're probably right about that.  I've been not wanting to announce because I don't know yet when it'll be done.  But, I guess, I can throw a webpage up and put a URL and short message asking for volunteers in my signature.

I mentioned it mostly because I need help.  I'm an okay c++ developer although still learning my way around the "boost" framework (which btw doesn't easily work in c++2011 and will eventually need to be hacked out of the code), but websites, forums, promotions, etc, I have limited knowledge of and need help.  

A bug database is needed but I don't really have time to administrate it.  

More developers would be a real help, in terms of testing and being able to respond to new bugs rapidly.  Also there's the "more eyes" thing, meaning that when a developer gets a bug report, it may be profoundly non-obvious to her why that bug is happening and how to fix it.  But when more developers see the same bug report, it'll likely be obvious to *somebody*, because they were in the middle of that code last week or because they had to learn about how something worked in order to fix something else a month ago, or ....  Just the simple fact of getting more eyes on it means there's a way to respond to more bugs.  

I mean, yes, I'm hacking a first cut of this thing together, but actually launching it really sort of requires a team.  I'm gonna be hella busy, and may not be able to keep up or do a good enough job, if I launch it by myself.

Holy crap, it's embarrassing to be in the same forum as this creepy-ass thread.

Guys: if you want to actually get together with a girl, it might help if you stop being creepy. 

My point is that when you demand change you have to demand change to something, and the something must work just as well, in both the long-term and the immediate senses, both to the society at large *AND* to the individual, as what you're changing from. 

That isn't defeatism; that's just acknowledging that the set of ideas that has competitive and practical advantages,  will, in the long run, win.

So develop an alternate proposal and show why it's in the self-interest of individuals in the middle of a capitalist society to switch to it.  Then show why it's also in the self-interest of family-size units in the middle of a capitalist society to change to it.  Then show why a whole society that changes to it will work more effectively than a society that doesn't, in such a way that the society that doesn't will progressively be disempowered relative to the one organized on the new paradigm. 

That is the absolute minimum requirement for a new idea to replace the idea of money.  It must first be a better idea than money.

Money is the most horrible way to manage anything - except for all the other ways we, as a global civilization, have ever attempted.

You're probably right that the current system is heading for destruction. That doesn't change the fact that there is no way to change it until there is something that provides the same or better advantages that can stand as a replacement. Believing that the current system is bad will not provide a way for the believer to pay the bills and feed the family.

Even if you convince people of the coming and current destruction, they will need a way to interact with those who aren't convinced. And it has to be a way that doesn't diminish their power,or they will soon be eliminated. So if you don't have something like that, you may as well stop talking. Because if you don't,you can have no effect.

Your answer reveals that you did not understand.  Whatever you want to replace money with, has to work better than money in terms of allocating resources.  Your belief that money is doing a bad job will get you nowhere near breaking it unless you can cast something that does a better job in terms of self-interest and productivity, *EVEN FOR THOSE WHO ARE NOT WILLING TO SUBJECT THEMSELVES TO IT*.  That's the self-reinforcement loop I was talking about.

That's why money is so powerful.  Even those who don't want to be subject to its limitations, ARE best served by paying attention to it.

Anyway, the whole point of mentioning that is to remind the OP what he's up against when he goes to try and break that spell.  That spell is millennia old, self-sustaining, and provides an organizing principle for most of our productivity and for most of the world's population.

Previous attempts to break that spell have caused the psychic infrastructure that depended on it (and the productivity of the people for whom it was broken, and the quality of their lives) to be significantly degraded.  The fact that these attempts have had so much influence is itself astonishing considering how ancient and powerful the spell is at this point. 

But the negation cannot persist in direct contact with the spell, because the negation does not have anything resembling an equally strong self-reinforcing feedback mechanism.  It may have superior memetic penetration, but it does not provide the organizing and structuring principles that Money does, and so those under the influence of the Money spell, consistently outcompete those who are not, eventually draining all vitality (and most physical resources as well) from those under the counterspell, inevitably eventually to the collapse of the counterspell itself.

I think the only way to counter the Money spell is to cast something greater.  What that would be I cannot imagine.  But it would have to provide the same kind of compelling organizing principle money provides - and the same kind of "inevitable win" in terms of resource allocation over those not subject to it that Money provides against all the counterspells that have been attempted so far.  In other words, it would have to be something that would allow a single family living in a society firmly committed to the principle of money, to allocate more resources than their competitors, creating a self-reinforcing feedback loop of superior power.

It may happen in the future if someone can develop an equally compelling spell, but I think that it's beyond anything that Humans can do at our current level of capabilities.

As every magician knows, "Money" is probably the most powerful spell ever cast. Whoever invented it, whether he (or she) realized it or not, thereby made himself (or herself) one of the most potent magicians in history.  Along with all the other magicians who cast it, in whatever places and at whatever times they did.

Like most magic, It is an idea.  Nothing more than that.  It happens purely inside people's heads, with absolutely no basis in physics or the world.   But its existence provides an organizing principle for all resource allocation, trade, and economics.   And therefore an organizing principle for many people's lives and a telling influence on all lives that have any contact with it.

Its value creates a self-sustaining feedback loop in which the fact that it *has* value, is itself valued.  To live among those who value money (and who value the fact that money has value) if you yourself are not subject to that spell, is to live at a disadvantage.  Not because of anything that's real in the world of physics and objective reality, but because of the idea itself.  Each generation teaches it to the generation that comes after, and each generation is deeply influenced by it in terms of their lives and capabilities and freedom. 

As a minor magician, I am sometimes able to say things that, by virtue of having been said, cause themselves to become true.  It's not exactly lying, and it's not exactly telling the truth.  Mostly I use it to enhance my partners' sexual pleasure - I tell her what I'm doing and the effect it's going to have on her, and behold -- I do the thing and exactly that effect happens.  Call it hypnosis if you like, I don't mind.  Magic is nothing less than using your mind, your power of communication, and the minds of others to sculpt the universe to conform to your will - and mostly consists in recognizing the relatively rare opportunities to do so. 

If, say, Ben Bernanke were an evil magician, he could say publicly, "The economy is going to tank in one week's time" and his statement, itself, would make his statement true.  But Bernanke isn't going to do that, because he's under the influence of a much larger, much older spell, which will not permit it.  And the name of that spell is Money. 

He doesn't want to live in a financially impoverished future and therefore, insofar as he is able, he avoids creating one.  At least he avoids doing so deliberately.  Doing so via incompetence can't really be helped by any spell cast by someone else besides him.

Huh.  I hadn't noticed those were tied to silver dimes.  I yam surprised.  Historically, though, Internet payment processing systems that involve someone holding precious metal have usually resulted in charges being filed -- everything from money laundering to fraud to failure to report to accounting irregularities to trading metal without appropriate state licensing, to etc etc etc.

Hope he manages to buck the trend.

I checked out the bitcoin source a couple weeks ago.

I've hacked colored coins into the daemon, blockchain, and protocol (they cannot be destroyed or 'decolored' by an unaware client that mixes them with other coins).  Including coin colors that are allowed to float against each other, and coin trades directly on the blockchain.  I envision a future in which these additional colors of coins are digital stocks and the system works as a distributed stock exchange.  

I've encrypted the protocol messages for privacy - all anyone can get is that you can tell by the pubkey what IP the message is for, but you cannot tell who's talking and you cannot read the message out of the protocol traffic. In principle you don't know what IPs are involved in a new transaction when it appears, but that can be compromised if an attacker adds enough "sybil" nodes to the network.

I've updated the source code and build defaults to c++2011.  

I've changed the reward structure to start out rewarding 4 coins (of color zero) per solved block and inflate the mining rewards at a rate of 3% a year forever, so there's no particular advantage for early miners.  

Now I'm elbows-deep in the code that selects coins, trying to make "standard" coin denominations - so the only denominations issued will start with 5, 10,  25, and 75, followed by some number of zeros. This makes it somewhat harder to "track" users by their transactions.  

After that I'm going to try fixing it so each transaction works (with no input from the user) like a little coinjoin between sender, receiver, and some fairly small random number of others.

I have plans to try to "fix" the mining algorithm so it's based on proof-of-stake rather than proof-of-work, and pays everyone who maintains an active full node approximately proportionally to the amount of coin they have, rather than paying one "winner" per round.  

After that I'm going to fix it so when transaction volume gets too high, the system splits into multiple blockchains and each client only has to listen to part of the traffic.  For example, if it needs to scale up to 2000 transactions per second,  you'd find the clients split into 25 "channels", each of which is listening to and serving 25 total blockchains - 24 of the total of 300 'normal'  blockchains and one 'universal' blockchain.  -- that is, one blockchain for every *other* channel, so that any two users would have at least one "normal" blockchain in common, and one blockchain that's shared among *all* channels, so that transactions involving clients in three or more different channels have a place where they can be.  That would mean each client has to download, verify, and store only one twelfth or so of the total 2000-per-second volume.  Which is still a lot, but which, by the time we get to 2000 transactions per second, I hope will be possible with "ordinary" hardware.  Each block would record the blockhashes of the most recent blocks found in the other blockchains.

After that I'm going to try and limit the tracked depth of the 'normal' blockchains.  Every 144 blocks or so (meaning approximately once per day) there'd be a larger "day block" that records the outstanding txouts.  And the depth of the blockchain down to that block would be all you need to download and keep when 'syncing' with the system.  Only the 'universal' blockchain would reach all the way back to the genesis block.

Once all of that is done, I'll be ready to launch beta version one.

Once I hack in 'awareness' of other coins' blockchains and atomic (if slow) distributed trading between different types of existing cryptocurrencies, I'll be ready to launch beta version two.  

Somebody could, in theory, start a cryptocoin "SilverOunce", limiting the number of coins issued to the number of ounces of (say) one-ounce silver coin blanks in his safe, and give a standing offer to swap of the cryptocoins for a one-ounce silver coin.

That cryptocoin would be backed by silver.  But it would also be centralized because he'd be the only one who could make new coins, he'd be paying for each coin by buying silver, and he'd be the only one offering to redeem them. 

Anyway, until someone does exactly that, it won't matter.  These aren't backed, they're merely rare.

Don't bother mining QRK any more, most of them are already mined and the reward is down to nearly negligible. 

You can use it as a good trading medium though; I think it's tending to go up relative to the value  of most altcoins.