# Can someone create a Bitcoin address that is identical to another except the last letter is lowercase where mine is capital

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?

• Ask them for the txnid (transaction id, aka transaction hash) and look that up (or if willing post it for others to do so) Commented May 1, 2022 at 4:37
• 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... Commented May 2, 2022 at 10:24

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.

• 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. Commented May 1, 2022 at 4:37
• @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. Commented May 1, 2022 at 12:45
• So to clarify if they "allegedly" made a deposit to the address they claim, what exactly would happen? Commented May 2, 2022 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. Commented May 2, 2022 at 12:33