Quote from: Loozik on February 26, 2014, 08:44:22 PM

Quote from: npiguet on February 26, 2014, 08:01:18 PM

You couldn't do that, because only one of the transactions would actually be in the block chain.

That would mean that valid transactions do not appear on blockchain - I consider this rubbish.

Quote from: cr1776 on February 26, 2014, 08:10:29 PM

Both transactions would be in the blockchain - the initial withdrawal and then the re-withdrawl request several weeks later which mtgox would have allowed.

I agree with this.

One needs to pair those two transactions (find them in the blockchain). There would be a few non-complex criteria for finding such malleable-looking transactions:
- amount of both must match
- date range should not be broad, e.g. the second transaction cannot be older than 1 day / week / month than the first one
- both transactions must be spent from an exchange address (not sure how to find such addresses but my guess is that such addresses generated a huge number of transactions for a short time)
- others

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It is a perfect research project for applicants who want grants from TBF.

There is no need for equal transactions (apart from the txid) to be present in the blockchain:

1) I ask for a withdraw of some amount of bitcoins
2) I alter the txid
4) I wait for the altered transaction to get confirmed
3) I ask Mtgox to credit those bitcoins back to my account because the transaction was not successful
4) go to 1

Best regards,
ilpirata79