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Author Topic: Why is it less safe to accept X confirmation deposits starting from July 22?  (Read 417 times)
blackdude
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July 24, 2017, 08:42:38 AM
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Is it because double-spends are now easier? Why are they easier?

I own a bitcoin business and have to decide whether it's worth it to reduce user-friendliness over security for my wallet. But I couldn't find any info really except 'it would be more prudent to'. What is the specific, technical reason?
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July 24, 2017, 10:21:16 AM
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Is it because double-spends are now easier?
Yes.

Why are they easier?
Because BIP91 requires miners to orphan blocks that do not signal BIP141 (SegWit), with the result that any transactions confirmed in such a block will become unconfirmed again, potentially allowing double-spending. The actual risk depends on how many miners are actually enforcing BIP91 and how many are signalling BIP141, which is difficult to determine with any certainty. As long as a significant number of miners are enforcing BIP91, non-SegWit blocks will probably be orphaned before getting a large number of confirmations, but transactions with a small number of confirmations are at risk of becoming unconfirmed at any time, and should be treated as unconfirmed transactions until they have many more confirmations.

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July 25, 2017, 12:51:48 AM
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If you require 1 confirmation, and accept a payment, and the transaction is confirmed in a non-SegWit block, it may appear to have 1 confirmation, and you might ship your goods. However, since much of the network will reject the block, and the rest of it will when the SegWit chain outgrows it, the transaction you got is no longer guaranteed to be in a block, and may go back to being unconfirmed. If you already shipped your goods, the buyer could initiate a double spend and potentially cheat you out of your money.

Waiting 5 confirmations means that your transactions are most likely not going to be reorganized out of a block, because it would probably have already happened by then.
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