Reverse transaction from bitcoin to an altcoin address

[Zocadas]

Didn't want to spam with my question to the other thread.
https://bitcointalk.org/index.php?topic=2268209.0
The OP of this thread sent Bitcoins from Bittrex to USDT address. I thought, such transaction is not reversible and money is lost. But some posters answered, that Bittrex, who owns private keys could reverse transaction.
How would that work?

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[DannyHamilton]

Didn't want to spam with my question to the other thread.
https://bitcointalk.org/index.php?topic=2268209.0
The OP of this thread sent Bitcoins from Bittrex to USDT address. I thought, such transaction is not reversible and money is lost. But some posters answered, that Bittrex, who owns private keys could reverse transaction.
How would that work?

You can't send bitcoins to a "USDT address".  You can send them to a bitcoin address, and that bitcoin address can be exactly the same address as an address that was generated by a USDT wallet.  This is because USDT and Bitcoin both use the same method for generating addresses:

• They both start with a randomly generated private key.
• Then, they calculate the public key from that private key using the same ECDSA algorithm.
• Then, they both hash that public key in the same way, and represent the resulting hash with base58check encoding.

As such, if you are in control of the USDT private key that was used to generate the USDT address, you can import that private key into a bitcoin wallet.  Since bitcoin uses the exact same process for generating an address from the private key, the bitcoin wallet will then have that exact same address as a bitcoin address (the bitcoin address that the bitcoins were sent to).

That bitcoin wallet will then have control of the bitcoins that were sent to that address.  That bitcoin wallet can then send those bitcoins.

[Zocadas]

Didn't want to spam with my question to the other thread.
https://bitcointalk.org/index.php?topic=2268209.0
The OP of this thread sent Bitcoins from Bittrex to USDT address. I thought, such transaction is not reversible and money is lost. But some posters answered, that Bittrex, who owns private keys could reverse transaction.
How would that work?

You can't send bitcoins to a "USDT address".  You can send them to a bitcoin address, and that bitcoin address can be exactly the same address as an address that was generated by a USDT wallet.  This is because USDT and Bitcoin both use the same method for generating addresses:

• They both start with a randomly generated private key.
• Then, they calculate the public key from that private key using the same ECDSA algorithm.
• Then, they both hash that public key in the same way, and represent the resulting hash with base58check encoding.

As such, if you are in control of the USDT private key that was used to generate the USDT address, you can import that private key into a bitcoin wallet.  Since bitcoin uses the exact same process for generating an address from the private key, the bitcoin wallet will then have that exact same address as a bitcoin address (the bitcoin address that the bitcoins were sent to).

That bitcoin wallet will then have control of the bitcoins that were sent to that address.  That bitcoin wallet can then send those bitcoins.

Thank you very much for your very helpful explanation. Already read through google about simply importing private key of USDT to Bitcoin wallet, but did not believe until I saw your answer. Now it makes sense to me, that Bittrex could help OP of this thread. Would that also work with Bitcoin and Bitcoin Cash?

[DannyHamilton]

Would that also work with Bitcoin and Bitcoin Cash?

Yes.

It will work with any variation that uses the same algorithm as Bitcoin for generating addresses.

Altcoins that want to avoid this problem will change the algorithm for address generation.  That way, the addresses for their system will be invalid if anyone accidentally tries to use is when sending bitcoins (and vice versa).

Unfortunately there have been quite a few lazy altcoin developers (and quite a few bitcoin forks that want to claim they are the "real" bitcoin), therefore sending a coin using an address generated for another coin is a common problem.