How does a site like Blockchain.info know which outputs are change?

Peter Todd

legendary

Activity: 1120

Merit: 1164

Quote from: Remember remember the 5th of November on November 28, 2013, 10:44:11 PM

Quote from: drawingthesun on November 28, 2013, 11:37:49 AM

Blockchain.info is very misleading.

The estimated transaction volume is trite, pure utter guess work.

Someone could buy a coffee and it could show up as a $100,000,000 transaction.

Also the IP address stuff is crap too, so misleading. The ip is the node that relays the transaction to the blockchain node and in no way represents where the actual transaction originated from.

Really? I actually tracked this guy that mined on top of the genesis blocks(orphans duh) using the IP address on the site, and he confirmed it was him.

That's a special case because no other node would have relayed those blocks; in the general case the IP addresses are bullshit.

Remember remember the 5th of November

legendary

Activity: 1862

Merit: 1011

Reverse engineer from time to time

Quote from: drawingthesun on November 28, 2013, 11:37:49 AM

Blockchain.info is very misleading.

The estimated transaction volume is trite, pure utter guess work.

Someone could buy a coffee and it could show up as a $100,000,000 transaction.

Also the IP address stuff is crap too, so misleading. The ip is the node that relays the transaction to the blockchain node and in no way represents where the actual transaction originated from.

Really? I actually tracked this guy that mined on top of the genesis blocks(orphans duh) using the IP address on the site, and he confirmed it was him.

Sukrim

legendary

Activity: 2618

Merit: 1007

Quote from: TooDumbForBitcoin on November 28, 2013, 11:33:39 AM

Quote

Also if there are e.g. a 3 BTC input and a 3 BTC input to a 4 BTC output and a 1 BTC output, the change is likely the 1 BTC, since there would have been no real need to combine the inputs otherwise.

That's some big fees, or I'm toodumbforbitcoin.

Yeah, I meant 2+3BTC inputs, not 3+3... Wink

scintill

sr. member

Activity: 448

Merit: 254

Quote from: maaku on November 28, 2013, 02:42:23 AM

Bitcoin-Qt is not the only wallet application...

Sure, I meant the probability skews a bit. In practice maybe it doesn't help much.

maaku

legendary

Activity: 905

Merit: 1012

Quote from: moderate on November 28, 2013, 01:38:11 PM

Quote from: maaku on November 28, 2013, 01:39:05 AM

If it were me, I'd do prime decomposition on the amounts, calculate their relative magnitude, a boolean value indicating whether they'd been seen before, etc., label a number of training examples, and have a support vector machine generate a classifier.

I'm so glad it is not you, that kind of thing is exactly someone fascinated with machine learning would go for. So many thousands and thousands of crap papers where guys blindly go after machine learning -- and it is mostly always svm --, without even considering other methods, reporting results close to 100% accuracy and other metrics just to find out that they don't even know how to setup training/testing sets, neither have a clue about the features they are using.

Yes, because when faced with a classic machine learning problem, the tried and true techniques of machine learning are not what you'd want to use.

piuk

hero member

Activity: 910

Merit: 1005

The logic is pretty simple:

- Remove all outputs matching any input addresses.
- If the transaction has one input take the smallest output.
- If a transaction has more than two inputs and exactly two outputs take the output with a value closest to the total input value.
- If a transaction has more than two outputs return the value of the smallest output.

Anyone is welcome to suggest improvements.

If you were really determined the accuracy could be improved by analysing the taint of the inputs used in the next transaction.

moderate

member

Activity: 98

Merit: 10

nearly dead

Quote from: maaku on November 28, 2013, 01:39:05 AM

If it were me, I'd do prime decomposition on the amounts, calculate their relative magnitude, a boolean value indicating whether they'd been seen before, etc., label a number of training examples, and have a support vector machine generate a classifier.

I'm so glad it is not you, that kind of thing is exactly someone fascinated with machine learning would go for. So many thousands and thousands of crap papers where guys blindly go after machine learning -- and it is mostly always svm --, without even considering other methods, reporting results close to 100% accuracy and other metrics just to find out that they don't even know how to setup training/testing sets, neither have a clue about the features they are using.

TooDumbForBitcoin

legendary

Activity: 1638

Merit: 1001

Not to mention their 650W/Gh/s electricity consumption nonsense. Every now and then the MSM picks that up.

drawingthesun

legendary

Activity: 1176

Merit: 1015

Blockchain.info is very misleading.

The estimated transaction volume is trite, pure utter guess work.

Someone could buy a coffee and it could show up as a $100,000,000 transaction.

Also the IP address stuff is crap too, so misleading. The ip is the node that relays the transaction to the blockchain node and in no way represents where the actual transaction originated from.

TooDumbForBitcoin

legendary

Activity: 1638

Merit: 1001

Quote

Also if there are e.g. a 3 BTC input and a 3 BTC input to a 4 BTC output and a 1 BTC output, the change is likely the 1 BTC, since there would have been no real need to combine the inputs otherwise.

That's some big fees, or I'm toodumbforbitcoin.

dserrano5

legendary

Activity: 1974

Merit: 1030

Plus, from what I've seen, bc.info doesn't bother with transactions having more than two outputs, the estimated amount is always the whole amount in the tx.

Sukrim

legendary

Activity: 2618

Merit: 1007

Also if there are e.g. a 3 BTC input and a 3 BTC input to a 4 BTC output and a 1 BTC output, the change is likely the 1 BTC, since there would have been no real need to combine the inputs otherwise.

Still it often guesses wrong, maybe there is some research potential in there somehow?

maaku

legendary

Activity: 905

Merit: 1012

Bitcoin-Qt is not the only wallet application...

scintill

sr. member

Activity: 448

Merit: 254

Quote from: maaku on November 28, 2013, 01:39:05 AM

If it were me, I'd do prime decomposition on the amounts, calculate their relative magnitude, a boolean value indicating whether they'd been seen before, etc., label a number of training examples, and have a support vector machine generate a classifier.

There's a million other ways you can do it and get decent results. Doesn't stop it from being a WAG though.

In a typical two-output tx created before ~2013-01-30, there's a good chance the first output is the change address. Maybe even longer, depending on how long until the fix was widely deployed.

maaku

legendary

Activity: 905

Merit: 1012

If it were me, I'd do prime decomposition on the amounts, calculate their relative magnitude, a boolean value indicating whether they'd been seen before, etc., label a number of training examples, and have a support vector machine generate a classifier.

There's a million other ways you can do it and get decent results. Doesn't stop it from being a WAG though.

gmaxwell

staff

Activity: 4284

Merit: 8808

Like a lot of other things on BC.i that are just guesses, its right often enough to confuse people.

ivroer

member

Activity: 89

Merit: 14

Quote from: jl2012 on November 27, 2013, 10:32:01 PM

That's just guestimation

Quote from: maaku on November 27, 2013, 10:35:07 PM

It makes a wild-ass guess.

Yup, +1 to these 2. It doesn't know it's a guess.

I imagine there's some guessing logic like, have any of the output addresses been seen on the blockchain before? Yes? It might be the actual "spend"... there might be more logic depending on the ratio of amounts to each address.

But it definitely does not get it correct every time, I've seen plenty of transactions (of my own) where the it has estimated incorrectly.

maaku

legendary

Activity: 905

Merit: 1012

It makes a wild-ass guess.

jl2012

legendary

Activity: 1792

Merit: 1111

Quote from: hayek on November 27, 2013, 09:53:38 PM

I can't find anything on the wiki about transaction change.

I know what it is but how does it appear any different than other outputs?

That's just guestimation

hayek

sr. member

Activity: 370

Merit: 250

I can't find anything on the wiki about transaction change.

I know what it is but how does it appear any different than other outputs?

Topic: How does a site like Blockchain.info know which outputs are change? (Read 1575 times)