I was speaking to a friend that mentioned that there were issues with pre-forked Bitcoin coins from Aug 2017 that never moved. He wouldn't tell me exactly what the potential issue was, but what were some discussed or potential issues with these unmoved pre-fork UTXOs?

Is it a potential double spend that could happen on these coins that never moved?

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    A potential issue I can imagine is that if you have BTC coins that never moved since the BTC-BCH fork, and you want to sell the BCH side using a recovery tool, you'll need to expose your private key to it - and that private key can be used to access your BTC as well. That's obviously a risky proposition, and it's better to use trustworthy software regardless. Still, my advice would be to move the BTC coins before trying to recover BCH; not for replay risk, but to avoid needing to expose a potentially live private BTC key. – Pieter Wuille Feb 9 at 19:10
  • Didn't the exchanges at that time have to modify their bitcoin software to extract these forked coins at one point? – Patoshi パトシ Feb 10 at 14:31
  • Possibly, but that was just due to the fact that BCH signatures worked slightly differently (and that's exactly what brings the replay protection). – Pieter Wuille Feb 10 at 16:21

No, there is no such problem. When BCH developers thought about introduction replay protection, they first agreed on the OP_RETURN-based one. Then they changed their minds and decided to use the better SIGHASH_FORKID-based one (see details about BCH replay protection).

Their first replay protection wasn't removed. It expired with block 530,000. After that block, unless you had moved your coins, it would have been impossible to separate your coins using that method.

That didn't matter to anyone then, since the second replay protection method introduced was made mandatory and worked perfectly. It was actually good enough to be exemplary (Bitcoin Gold copied it).

If you have pre-2017 coins, then you have BTC, BCH, BCHA, and BCHSV. To split those, send your bitcoins and BCHs to Coinex and they'll split it for you. (It is suggested to check that your transactions don't have nLockTime.)

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