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Author Topic: How to stop 'double spend' attack  (Read 3697 times)
Benjig
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July 08, 2014, 03:30:21 AM
 #61

FYI, also check out updown's post in the updown thread on July 1.  It says their wallet was cleaned out recently due to double spend attack.  Wow.  Maybe they are trying to get back at people who stole money from them with double spending?

Yeah, so who are making this vicious attacks? and how are they making them?
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July 08, 2014, 05:00:55 AM
 #62

http://nottm28.imgur.com/all/

Sorry - made them publically viewable now...

The album is missing. Please reload it. I would like to research this myself. This fits into a Ghash.Io casino attack senario I'm researching.

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nottm28 (OP)
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July 08, 2014, 08:32:40 AM
 #63

When I checked this morning the missing txns were back - http://nottm28.imgur.com/all/

I think someone noticed a double spend attack from updown and somehow suspended all txns from the last 2 weeks. Now they have been released.

This is some scary shit...

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BitCoinDream
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July 08, 2014, 03:29:35 PM
 #64

When I checked this morning the missing txns were back - http://nottm28.imgur.com/all/

I think someone noticed a double spend attack from updown and somehow suspended all txns from the last 2 weeks. Now they have been released.

This is some scary shit...

So the reason for the anomaly is still a mystery or it has been discovered ?

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July 08, 2014, 04:05:09 PM
 #65

Bitcoin crash ? so is this the right moment for change myself and all my Bitcoins to FIAT ?  Cry
Keyser Soze
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July 08, 2014, 04:17:58 PM
 #66

When I checked this morning the missing txns were back - http://nottm28.imgur.com/all/

I think someone noticed a double spend attack from updown and somehow suspended all txns from the last 2 weeks. Now they have been released.

This is some scary shit...

So the reason for the anomaly is still a mystery or it has been discovered ?
It was an issue with his wallet not showing all the transactions. The blockchain.info warning he was seeing on some addresses doesn't necessarily mean anything.
nottm28 (OP)
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July 08, 2014, 04:24:42 PM
 #67

When I checked this morning the missing txns were back - http://nottm28.imgur.com/all/

I think someone noticed a double spend attack from updown and somehow suspended all txns from the last 2 weeks. Now they have been released.

This is some scary shit...

So the reason for the anomaly is still a mystery or it has been discovered ?
It was an issue with his wallet not showing all the transactions. The blockchain.info warning he was seeing on some addresses doesn't necessarily mean anything.

Nah I'm not willing to believe that - it was only the updown txns that were affected - if was a problem with my own wallet then why with only updown? Also I only saw the double spend warning with txns associated with updown. You explanation is far from satisfying.

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Keyser Soze
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July 08, 2014, 04:37:07 PM
 #68

Nah I'm not willing to believe that - it was only the updown txns that were affected - if was a problem with my own wallet then why with only updown? Also I only saw the double spend warning with txns associated with updown. You explanation is far from satisfying.

It is not possible for select transactions, with many confirmations, to suddenly become unconfirmed in the blockchain and then disappear from your wallet. There is no way to "suspend" the transactions like you have suggested before. They either are confirmed or unconfirmed. Do you have an issue with a specific transaction? If so, what is the transaction id (not the address) and what problem do you think exists?

Also, as I previously stated, that warning you may see on blockchain.info doesn't necessarily mean anything.
nottm28 (OP)
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July 08, 2014, 04:45:49 PM
 #69

Nah I'm not willing to believe that - it was only the updown txns that were affected - if was a problem with my own wallet then why with only updown? Also I only saw the double spend warning with txns associated with updown. You explanation is far from satisfying.

It is not possible for select transactions, with many confirmations, to suddenly become unconfirmed in the blockchain and then disappear from your wallet. There is no way to "suspend" the transactions like you have suggested before. They either are confirmed or unconfirmed. Do you have an issue with a specific transaction? If so, what is the transaction id (not the address) and what problem do you think exists?

Also, as I previously stated, that warning you may see on blockchain.info doesn't necessarily mean anything.

Well I also thought it was not possible to unconfirm a transaction that had hundreds of confirmations - but it must be possible. Isn't that what they did when the blocked chain forked last year - they rolled back to a point in time and all txns up to that point were lost.

As previously stated - I no longer have any issues with any txns. I did have an issue yesterday and I posted a large pile of txn ids if you actually want to read the thread.

Also as previously stated - the fact that you state the warnings I was seeing regarding the missing updown txns does not necessarily mean anything is far from satisfying. They could mean something and you stating that they might not doesn't add anything. Unless you actually knew what they meant. Which you dont.

So all of my questions remain unanswered.

[edit] see for yourself here

http://nottm28.imgur.com/all/

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Keyser Soze
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July 08, 2014, 06:02:14 PM
 #70

Well I also thought it was not possible to unconfirm a transaction that had hundreds of confirmations - but it must be possible. Isn't that what they did when the blocked chain forked last year - they rolled back to a point in time and all txns up to that point were lost.
That is why I used the word selected. It is not possible for one specific transaction in a block to become unconfirmed while the rest in the same block are unaffected.

As previously stated - I no longer have any issues with any txns. I did have an issue yesterday and I posted a large pile of txn ids if you actually want to read the thread.
I looked at some of the transactions, but did not see any issues with double spending, even when you were still experiencing the problem yesterday. I admit I did not look through them all or maybe I missed something.

Also as previously stated - the fact that you state the warnings I was seeing regarding the missing updown txns does not necessarily mean anything is far from satisfying. They could mean something and you stating that they might not doesn't add anything. Unless you actually knew what they meant. Which you dont.
That blockchain.info warning shown on an address (it doesn't appear on transactions) can happen when unconfirmed coins are spent and blockchain.info thinks they may never be confirmed. The warning went away because the transaction(s) in question received a confirmation. (If I am wrong about the blockchain.info's warnings, please let me know.)

[edit] see for yourself here

http://nottm28.imgur.com/all/
The only difference in the two wallet screenshots is one (https://i.imgur.com/TdZfNG1.png) is missing transactions that the other (https://i.imgur.com/fyQCrWR.png) has listed. It seems the wallet fixed itself after the corrupted data issue was resolved and it was fully synced.

So all of my questions remain unanswered.
What questions do you still have?
nottm28 (OP)
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July 08, 2014, 06:23:11 PM
 #71

I looked at some of the transactions, but did not see any issues with double spending, even when you were still experiencing the problem yesterday. I admit I did not look through them all or maybe I missed something.

Other people clearly stated they could also see some of the double spend warnings - I wasn't seeing things - so maybe you did miss it.

Quote
That blockchain.info warning shown on an address (it doesn't appear on transactions) can happen when unconfirmed coins are spent and blockchain.info thinks they may never be confirmed.

Most of the transaction ids I posted had already been confirmed, some in their hundreds. How can the block chain think a txn with hundreds of confs might never be confirmed?

Quote
The warning went away because the transaction(s) in question received a confirmation. (If I am wrong about the blockchain.info's warnings, please let me know.)

As above, the txn(s) in question were already solidly confirmed. So why was the warning there in the first place for a well aged txn?

Quote
The only difference in the two wallet screenshots is one (https://i.imgur.com/TdZfNG1.png) is missing transactions that the other (https://i.imgur.com/fyQCrWR.png) has listed. It seems the wallet fixed itself after the corrupted data issue was resolved and it was fully synced.

I restored the wallet from a backup and resynced the last weeks worth of txns - it didn't take long to fully sync - yet hours and hours later the updown (and only the updown) txns were showing n/a for address and txn id. And these were the addresses showing the double spend warnings.

Quote
What questions do you still have?

1) Can a set of transactions to a specified btc address be reversed?
2) If so, how is that done?
3) If so, who does it? - and under what circumstances?
4) If so, how secure is the process? Is it susceptible to a malicious actor?
5) What is the trigger for blockchain.info to show this double spend warning for an address?
6) Can I be sure (even after hundreds of confs) that a payment I recieve has really been recieved?
7) Would you be so nonchalant if you were watching txns disappear from your own wallet?

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nottm28 (OP)
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July 08, 2014, 06:30:48 PM
 #72

8. How can I (if at all) defend myself from someone performing a double spend attack when sending me coins?  (like the OP topic states)

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Keyser Soze
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July 08, 2014, 07:21:36 PM
 #73

Other people clearly stated they could also see some of the double spend warnings - I wasn't seeing things - so maybe you did miss it.
Most of the transaction ids I posted had already been confirmed, some in their hundreds. How can the block chain think a txn with hundreds of confs might never be confirmed?
As above, the txn(s) in question were already solidly confirmed. So why was the warning there in the first place for a well aged txn?
That blockchain.info warning may have been in error or maybe your browser was loading an older version of the page from its cache. Blockchain.info is just a website and has been known to have issues from time to time.

I restored the wallet from a backup and resynced the last weeks worth of txns - it didn't take long to fully sync - yet hours and hours later the updown (and only the updown) txns were showing n/a for address and txn id. And these were the addresses showing the double spend warnings.
Your wallet was probably not finished, or it would have shown all the transactions correctly.

1) Can a set of transactions to a specified btc address be reversed?
2) If so, how is that done?
3) If so, who does it? - and under what circumstances?
4) If so, how secure is the process? Is it susceptible to a malicious actor?
6) Can I be sure (even after hundreds of confs) that a payment I recieve has really been recieved?
Once a transaction receives a confirmation (is included in a block), it is irreversible.

5) What is the trigger for blockchain.info to show this double spend warning for an address?
See:
That blockchain.info warning shown on an address (it doesn't appear on transactions) can happen when unconfirmed coins are spent and blockchain.info thinks they may never be confirmed. The warning went away because the transaction(s) in question received a confirmation. (If I am wrong about the blockchain.info's warnings, please let me know.)

7) Would you be so nonchalant if you were watching txns disappear from your own wallet?
If I knew they already had confirmations, I would know it is an issue with my wallet. While it may be annoying or take time to fix, I know my coins would be there.

8. How can I (if at all) defend myself from someone performing a double spend attack when sending me coins?  (like the OP topic states)
Don't rely on the transaction until it is confirmed. Once it is confirmed, it is yours until it is spent.
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July 08, 2014, 07:32:50 PM
 #74

8. How can I (if at all) defend myself from someone performing a double spend attack when sending me coins?  (like the OP topic states)

You can't do it. The system is supposed to do it for you. Rational actors are supposed to preserve the system but as we all know people don't always live up to our version of rational.

I don't believe you were the victim of a double spend. It's more likely that your original bootstrap.dat file became corrupted. You then downloaded it over the corrupted copy adding to the problem. Did you finally delete the old copy of bootstrap.dat or rename it bootstrap.old? If I were you I would save my wallet.dat file, delete all Bitcoin folders, download a fresh copy of QT, copy over the old wallet.dat, and resync with the network.

nottm28 (OP)
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July 08, 2014, 08:04:21 PM
Last edit: July 08, 2014, 08:16:42 PM by nottm28
 #75

...snip...

Your guesses are useless and give me nothing - I'm hoping someone who actually knows something might answer (some of) my questions...

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nottm28 (OP)
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July 08, 2014, 08:16:09 PM
 #76

8. How can I (if at all) defend myself from someone performing a double spend attack when sending me coins?  (like the OP topic states)

You can't do it. The system is supposed to do it for you. Rational actors are supposed to preserve the system but as we all know people don't always live up to our version of rational.

I don't believe you were the victim of a double spend. It's more likely that your original bootstrap.dat file became corrupted. You then downloaded it over the corrupted copy adding to the problem. Did you finally delete the old copy of bootstrap.dat or rename it bootstrap.old? If I were you I would save my wallet.dat file, delete all Bitcoin folders, download a fresh copy of QT, copy over the old wallet.dat, and resync with the network.

Yesterday I thought I was the victim of a double spend. Today all seems well. That's a bit worrying on its own for me - one day broke next day fine no explanation kind of thing.

When I got the corrupt wallet message I said yes - re-download the entire chain. After I while I got bored, shutdown the client and restored my \AppData\Roaming\Bitcoin folder (after moving the existing one out the way) to a backup I took 7 days ago. When I fired up the client, it said 7 days out of sync as expected. Everything looked normal. As the last 7 days came through I was noticing that the updown txns were showing n/a for txn id and address. Just updown. I can understand if a client is not synching random txns - but this was only the updown ones. Slush and other payments I have sent and recieved were all shoing fine. Getting worried, I block chained some of the updown txn ids and found these double spend warnings. Others seen them too from their own browsers when they checked out the txn ids I posted. That rules out browser cache. That rules out me being an idiot. I welcome your theory but it doesn't give me any kind of warm feeling...

[edit] I back up my wallet.dat file to offline once a week too - but since I restored the entire bitcoin folder I didn't do anything manually with the wallet.dat

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July 08, 2014, 09:00:16 PM
 #77

...snip...

Your guesses are useless and give me nothing - I'm hoping someone who actually knows something might answer (some of) my questions...

I suppose I shouldn't have wasted my time with "useless" answers. Insulting people trying to help you usually doesn't get you far...
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July 08, 2014, 09:04:29 PM
 #78

...snip...

Your guesses are useless and give me nothing - I'm hoping someone who actually knows something might answer (some of) my questions...

I suppose I shouldn't have wasted my time with "useless" answers. Insulting people trying to help you usually doesn't get you far...

No insult intended - but you seemed to be repeating the same thing with no apparent knowledge of what you are talking about...

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July 08, 2014, 09:12:32 PM
 #79

...snip...

Your guesses are useless and give me nothing - I'm hoping someone who actually knows something might answer (some of) my questions...

I suppose I shouldn't have wasted my time with "useless" answers. Insulting people trying to help you usually doesn't get you far...

No insult intended - but you seemed to be repeating the same thing with no apparent knowledge of what you are talking about...

Multiple people are trying to explain u with reasoning. I'm sorry to say, that your adamant attitude is extremely unwelcome.

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July 08, 2014, 09:32:39 PM
 #80

Multiple people are trying to explain u with reasoning. I'm sorry to say, that your adamant attitude is extremely unwelcome.

Well I'm sorry you think that - but "ah it will be OK" doesn't help me and I'm frustrated that no-one seems to know the answers. We all just 'hope' that "ah well it will be OK"...

Anyone who probes is obstricised. I don't mind standing out and asking the questions that we should know the answer to but - we don't.

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