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The reason I ask is an online casino was set to pay me $1,000 via Bitcoin and showed me the address they claim to have paid, which is identical to mine except the very last letter is capital and on mine it's a lower case. Is it possible to create another address so similar to mine?

Jerry
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  • Ask them for the txnid (transaction id, aka transaction hash) and look that up (or if willing post it for others to do so) – dave_thompson_085 May 01 '22 at 04:37
  • Thank you. I know it sounds like a stupid question to you guys but I feel I'm being lied to by these guys and just wanted to clarify before I pursue my funds any further. They said only finance dept has that info and of course they never return my calls, msgs, emails ect... – Jerry May 02 '22 at 10:24

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It is not possible to have two valid Bitcoin addresses that differ only in their last 5 characters at all, as those only contain checksum data. For bech32/bech32m addresses (bc1...), that's even true for the last 6 characters.

In theory, it is possible to construct two P2PKH (1...) or P2SH (3...) addresses that differ only in 1 character if not at the very end, but the probability is very low that any given addresses has such a valid mutation (1 in ~75 million). With bech32/bech32m any two valid address differ in at least 5 characters.

Pieter Wuille
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  • Where do you get ~100million? Odds against the check being the same is 2^32 which is just over 4billion. And that's only after you found two pubkeys, or scripts, that hashed to near-identical values, which is only a little less than the birthday bound, maybe 2^120 against i.e. won't happen in this universe. – dave_thompson_085 May 01 '22 at 04:37
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    @dave_thompson_085 2^32 / 57 (because there are 57 distinct single-position errors). And by valid I meant "checksum valid", ignoring whether anyone else might have the private key for it. This is what matters for not accidentally sending your coins into the void. – Pieter Wuille May 01 '22 at 12:45
  • So to clarify if they "allegedly" made a deposit to the address they claim, what exactly would happen? – Jerry May 02 '22 at 10:26
  • @Jerry Nothing, that would not be a valid address, and there is no way to send anything to it. Either their software is horribly broken, or they are lying. – Pieter Wuille May 02 '22 at 12:33