Advantage of coin control, response to Mike Hearn

[nimda]

• Use youngest coins (aged coins are a resource)

Why would you care if the coins are old or young?  Why are aged coins a resource?

The age of inputs is a factor in calculating transaction priority. With a 1 week old 1 BTC coin, you can spend 5+ SatoshiDICE dust inputs for free.

[etotheipi]

Maybe I am missing something.  Does Armory have this already?  Why do you want a change to the Bitcoin software if this be done by a wallet or plugin that sits on top of the main software? 

Armory lets you control the source addresses, not the individual coins (but still called "Coin Control").  People requested "Coin control", I gave them that, and I haven't really heard any complaints.  So I left it alone.

I think I understand, maybe:  Some people say that one Bitcoin is just like another (just like atoms in quantum mechanics where you can't distinguish one from another) but that is not really true.  Each satoshi has a history which can be traced back to the point it was mined.  With the Armory "coin control" it allows you to control the balances in the individual addresses but not each satoshi within each address.  What coin control would do is allow control over each individual Satoshi.  It seems to me that a wallet could do coin control without changing the main Bitcoin client but it would be a complicated programming task (but not impossible).  However, it may be easier to implement coin control if the main client was changed to make it easier to have coin control.  Is this the issue?

If you never reuse addresses, it is identical.  I wouldn't think of it as controling each satoshi... every time you receive X BTC, that's like an $X-bill (if $1/BTC) now sitting in your wallet.  When you want to give someone 10 BTC (assuming X is more than 10), you sign a transaction that uses that $X-bill as input, and has two outputs:  assigning 10 BTC to their address, and assigning X-10 to a change address you own.  Now they have a 10-BTC bill in their wallet, and you have an (X-10)-BTC bill in your wallet.  The original bill is "spent" (never to be used again).

Really, your signature allows you to destroy X-BTC bills, and create new bills with new owners equal in size to the original (anything left over is claimed by the miner that mines the transaction as a fee).  Armory coin control basically says "I only want to use bills from these N addresses, no others".  The intent was to give users control over what addresses are linked when you create transactions.  Some people want more than that, and want to control individual bills... Armory doesn't have that.

[Dabs]

• Use youngest coins (aged coins are a resource)

Why would you care if the coins are old or young?  Why are aged coins a resource?

The age of inputs is a factor in calculating transaction priority. With a 1 week old 1 BTC coin, you can spend 5+ SatoshiDICE dust inputs for free.

Would you have an easy chart on how this works? Say, for every day (or 144 block) equivalent of 1 BTC, how many SatoshiDICE dust inputs can be spent for free. Will this also convert to, for example, a 1 block old 144 BTC? And a 6 block old (1 hour) 24 BTC. 2 block old 72 BTC. 3 block old 48. 12 block old 12 BTC. etc?

[nimda]

• Use youngest coins (aged coins are a resource)

Why would you care if the coins are old or young?  Why are aged coins a resource?

The age of inputs is a factor in calculating transaction priority. With a 1 week old 1 BTC coin, you can spend 5+ SatoshiDICE dust inputs for free.

Would you have an easy chart on how this works? Say, for every day (or 144 block) equivalent of 1 BTC, how many SatoshiDICE dust inputs can be spent for free. Will this also convert to, for example, a 1 block old 144 BTC? And a 6 block old (1 hour) 24 BTC. 2 block old 72 BTC. 3 block old 48. 12 block old 12 BTC. etc?

The Wiki has a technical explanation, but I'll try to simplify it. You must multiply number of satoshi's (10^-8 BTC) by number of confirmations and divide that by the total number of bytes to get priority. If the priority is greater than a 1 day 1 BTC coin (144 confs * 10^8 / 250 bytes), it can be free.

Now in reality, since compressed keys can be used, a transaction can be less than 250 bytes (min 225 for a standard one-input two-output tx).
Also, the number of bytes added by one more input varies greatly. Compare
http://blockchain.info/tx/8be6d23b774c9a5934c3a1927754e3fca4c98d6d95de7666a7f12df1d06f9b31
with
http://blockchain.info/tx/27bf16c3febd2c668ac867e378ca3fd9880a16cb969d4d54015553ed64416e95
to see what I mean. Both have 2 inputs and 2 outputs, yet there's a 64-byte difference between them.

If you give yourself a good cushion, though, you'll be fine. The easiest way is to use one bitcoin-day per input. If you're spending a dust tx, make sure you have 2 bitcoin-days. If you're spending 10 dust tx's, use 11 bitcoin-days. All bitcoin-days are created equal (except some days have more blocks than others; this is near-negligible). A 20-day 0.05 BTC has the same priority as a 1 day 1 BTC input.

Caveat: never create a sub-0.01 BTC output, no matter the priority.

I hope that was clear enough. If not, ask away!


P.S. The fee rules are not set in stone. Some miners have custom fee rules, and the rules in the reference client may soon change.

[Dabs]

100 day old 0.01 BTC is the smallest then, and 10 minute old 144 BTC is largest. If I have 19 dust, I should use 20 bitcoin days. Going to the extremes, I'd need 2000 day old 0.01 BTC, or 2880 BTC if I want it next block.

[mp420]

Why I want coin control:

I understand keypairs.

I understand (on a basic level) how the blockchain and transactions work.

I do not understand the abstractions such as "accounts" built on bitcoin that the client imposes on me. They are neither something from the financial world nor something from the cryptography world. I can't see how they are useful and frankly I don't WANT TO learn how to use them.

I think a more sophisticated "accounting" system on top of the raw protocol could be useful if you are building a payment processing system on top of Bitcoin. I, as an end user, expect to do transactions very rarely and to spend a lot of time preparing whenever I have to make a transaction. Such as installing the newest client and downloading the blockchain.

So, what I want is:

1. The ability to import privkeys, preferably in many formats.
2. The ability to make raw transactions.

What I would like on top of those:

3. All kinds of "are you really really sure" warnings for anything that would be broadcast over to the network. Maybe even a configurable delay so that I could back out if I notice I made a mistake.

I do not want to keep any kind of a hot wallet, thank you very much. And I think the addressess (pubkeys) are a very useful thing to know, so I can check my balances from any third party service.

I do not want to run a node continuously.

[Dabs]

Coin Control is more fun!



Keep the output to less than 10k (or about 62 unspent) and you have no fee too.