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Author Topic: Is it possible to have two transaction IDs that are exactly the same?  (Read 2637 times)
TeraPool
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July 13, 2011, 01:20:18 AM
 #1

Or would that be considered a collision of some sort? What exactly is a transaction id? A hash of some sort I presume?

I couldn't find much about transaction ids in particular on the wiki.

How would the bitcoin client treat two separate transactions with identical transaction ids?

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July 13, 2011, 01:50:21 AM
 #2

Yes, it is possible... But is very very very unprobable. They are more possible directions that atoms on the hole earth, but im not really sure.

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TeraPool
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July 13, 2011, 03:44:26 AM
 #3

Thanks for that.

That's what I thought.

Since blockexplorer allows you to search by transaction id... you should not be able to have a duplicate one I would think.

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theymos
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July 13, 2011, 03:58:37 AM
 #4

Transaction IDs are SHA-256 hashes of transactions. It's very safe to use them as unique IDs, and it's a waste of time to try to detect collisions.

It is possible (though very rare) for the exact same transaction to appear twice in the block chain, however.

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davux
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July 13, 2011, 07:44:02 AM
 #5

It is possible (though very rare) for the exact same transaction to appear twice in the block chain, however.

Can you please explain under what circumstances this could happen? I couldn't find anything.

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Maged
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July 13, 2011, 07:52:51 AM
 #6

It is possible (though very rare) for the exact same transaction to appear twice in the block chain, however.

Can you please explain under what circumstances this could happen? I couldn't find anything.
See blocks 91812 and 91842 for one example.

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July 13, 2011, 02:47:23 PM
 #7

You can maliciously, or stupidly, create two transactions with the same ID. The easiest way is to mine two blocks and include in each one only a single transaction -- the coinbase transaction, with the same payout address, same payout amount, and the same coinbase.

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