Do Bitcoins have Serial Numbers (effectively)

[jonone100]

I'm a bit confused about this.

I've found a post from Gavin in reply to ribuck saying:
"Quote from: ribuck on January 25, 2011, 03:17:27 pm
The analogy doesn't stretch further than being a cute graphic. Individual bitcoins don't exist in any meaningful way, nor do the individual specks of bit-dust. There is no notion of 21 million coins, numbered 1 to 21,000,000.

"Sure there is-- block 0 contains coins 0-49, block 1 coins 50-99, etc.

If you get sent 500 bitcoins, they can all be traced back to generation transactions, so you "own" a bunch of little pieces of land in bitcoin-world."

The (otherwise excellent article in the economist) says:
'Bitcoins do not resemble banknotes with unique serial numbers.'


Of course, I'm inclined to take what Gavin says over anyone else, but I want to make sure I'm not misunderstanding this.

I had in my mind the idea that each bitcoin could be traced back through all its transactions to its generation (no matter wether it was mixed with other bitcoins or not).


I'm a money freak wanting to write another blog post about bitcoin. Already posted a question about the inclusion of transactions in the block chain to which I received a very helpful answer. Your thoughts are appreciated.
-Jon

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[Buzzard]

Tracking individual BTC isn't really feasable (they get split up into smaller units easily), but if one wanted to, the Satoshi (sp?) could be tracked, since it's the smallest possible unit.  (Think grains of sand, instead of coins/bills)

Yes, by going back through the block history, every last transaction is there.

[Insti]

I'm a bit confused by your quoting.

Anyway:

If I put 2 coins from address 'A' and 1 coin from address 'B' into a new address 'C'
Then I spend the 3 from 'C':  1 to 'D' and 2 to 'E'

Where did the coin in address 'D' come from? 'A' or 'B'?

[drsaul]

Caveat: I'm not an expert.

Yes you're right, each fraction of coin can be traced back to where it came from: a block with generated BTCs at some point in the past.  

Not true for dollars, the serial number only tells you where that particular piece of paper was minted - nothing about where the value really came from before it was spit out of your ATM.  

I've seen tons of blatantly false information in the media about this.. claiming that bitcoins are "less traceable than dollars".  As I understand it, they truth is that they are more traceable than dollars.  

[jonone100]

Thanks for the swift replies.

~yes the formatting didn't work on the quotes. sorry.

for clarity here is the actual message http://forum.bitcoin.org/index.php?topic=2965.msg41319#msg41319
 
Buzzard: you seem to be saying that we can tell from which bitcoin each Satoshi was born? And so therefore we can also tell in which block any bitcoin was generated. And indeed if I understand Gavin correctly, where the coin was generated in the sequence of 50 (as it is at the moment).

Insti: thanks, but you don't really answer my question - I guess that's my fault for making Gavin's quote so unreadable.

drsaul: thanks. Yeah I really don't want to contribute to false information about bitcoin.

[Buzzard]

Traceable - Oh gods, yes.  Right back to the creation.

Anonymous - Yes.  We're running around with something akin to numbered Swiss Bank accounts.

The system is set up so that every transaction is visible, but matching a transaction to a person gets a little difficult.
As my signature, I've got ONE of my account numbers listed.  Unless I screw up, it'd be a little difficult to casually trace down the rest of my accounts.  (Yes, I can be that paranoid about my details)
Add to the difficulty, the ability to generate new accounts with the press of a button, and things get mighty interesting.


As for where any particular unit came from...  Just think of random grains of sand.  All identical, and we trade them by the bucket-full.

[jonone100]

So, is it fair to say that Bitcoin can be more accurately described as Bitnote?

I don't mean to be provocative (well, may be a little bit).

Notes have unique serial numbers, whereas coins do not.

(I'm not concerned here with the traceability of accounts, just the nature of Bitcoin)

Your comments are appreciated.

[Stephen Gornick]

"Sure there is-- block 0 contains coins 0-49, block 1 coins 50-99, etc.

Just to make sure it is clear:
 - http://blockexplorer.com/block/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
The miner of Block 0 was awarded 50 bitcoins to a single bitcoin address that was generated, 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa.

All bitcoin currency that exists and will ever exist was issued as a block reward, which is currently 50 BTC but will be dropping to 25 BTC per block in about 18 months.

Incidentally, those bitcoins have not yet been spent.

[jonone100]

thanks Stephen.

I'm afraid I'm still a little unclear though.

When a block is created and 50 BTC sent to an address, it is possible to see whether those BTC have been spent, and if they have been, to see where they were sent. (Of course, you don't know who owns the address). But is it then possible to follow those same 50 BTC (or parts thereof) through subsequent transactions?

Also, the 50BTC created : are they a coin that is indistinguishable from any other coin in the block, or a coins that are sequentially numbered (i.e. notes) (as Gavin's post seemed to suggest, to me at least)

As I said, I'm not concerned here with privacy issues etc, I just want to understand the nature of Bitcoin.


I'd really like a yes/no answer if possible. So perhaps it may help if I rephrase the question.

Is a bitcoin uniquely identifiable against any other bitcoin?

I've read some things that suggest that a bitcoin doesn't really exist without an associated address which would suggest that all bitcoins are the same. On the other hand I've also read things (such as Gavin's post) that suggest that Bitcoins are unique.

I don't have the technical expertise to understand the code used so I not able to find the answer for myself.

[joan]

Understand that a transaction can have multiple inputs and multiple outputs.

So you could have a transaction spending 100 BTC defined by :

A (25) + B (75) ==> C (45) + D  (55).

When considering the output C for example, there is no way to track how much of the 45 BTC are coming from A, and how much coming from B.
You can still track the inputs recursively and they will eventually go back to some generation transactions. But this is not a clear path from one BTC in this transaction to its ancestor in the generation transaction.

As soon as a BTC leave its generation TX, it stops being a tangible thing. It is only defined by the chain of ownership, with the uncertainty described above.

[theymos]

They're not really numbered. Gavin was saying that they could be numbered by an external system, though the numbering system would be arbitrary. You'd have to come up with arbitrary rules for certain ambiguous circumstances. There is no one true number for a certain coin.

[$G]

I am also interested in this matter. Can we then confirm that there is no identification number associated to each "satoshi"? Is it also safe to assume it would be impossible for an external system to assign such a number, as the bitcoin system is not equipped keep record of the path of individual units? Instead only tracking "lumped transactions involving two BTC addresses?

[Insti]

for clarity here is the actual message http://forum.bitcoin.org/index.php?topic=2965.msg41319#msg41319

Ok.
How does that thread not already answer your question?

As for what I was trying to say, as usual theymos says it better in that thread: http://forum.bitcoin.org/index.php?topic=2965.msg52466#msg52466

Is a bitcoin uniquely identifiable against any other bitcoin?

I think the answer to this question is 'no'.

Think of each bitcoin address as a bucket of water. If a bucket is created which contains 50 liters of water. If you combine 10 of these buckets into a big 500L tank, then take out 1L of water from the tank, you cannot tell which bucket the water started in. So therefore the water is not uniquely identifiable. It is the same with "bitcoins".

[renepost]

Thanks a lot for this quite thorough explanation, I guess it shows we sometimes need to 'unlearn' in order to fully appreciate the concept of bitcoin! My idea was as well that there would be some kind of numbering, but I see now the fluidity of the matter ;-) awesome.