Beginner's question on transactions

[stephanlorenzen]

Dear Forum,

I am reading "Bitcoin. Basics and Programming" by Andreas Antonopoulos and try to understand transactions. He claims that all the transaction examples in his book are real transcations.

As an example for a transaction, he gives the link https://oreil.ly/GwBq1 which is a payment of Alice to Bob. I see there that
- the input transaction is 4ac541802679866935a19d4f40728bb89204d0cac90d85f3a51a19278fe33aeb:1 worth 0.001 BTC
- 0.0002 BTC were paid to bc1p8dqa4wjvnt890qmfws83te0v3qxzsfu7ul63kp7u56w8qc0qwp5qv995qn
- 0.00075 BTC were paid to bc1qwafvze0200nh9vkq4jmlf4sy0tn0ga5w0zpkpg (this is the change, should be Alice's wallet).

So, I would expect that the wallet of Alice is bc1qwafvze0200nh9vkq4jmlf4sy0tn0ga5w0zpkpg

Thus, I would expect that the second output of the input transaction, 4ac541802679866935a19d4f40728bb89204d0cac90d85f3a51a19278fe33aeb:1, goes to Alice's wallet (that's where she took the money from). However, if I click on the input transaction, I see

- input transaction is e6264ea63c267f1d54ae0125020745356eb054fdec09c51fcc403d9f0ce95ac2:0 worth 0.18312922 BTC
- 0.18210494 BTC were paid to bc1q44c67v69aqlmv3hmw236uw0yjh2xvf9ssqnm5q (this is the change)
- 0.001 BTC were paid to bc1pyfw56zu5vsq0ulu9kytasgw4xwnm3eysll6tfdz8d9gtht97k7tqxsz78n -- This should also be Alice's wallet!

That looks like Alice's wallet is bc1pyfw56zu5vsq0ulu9kytasgw4xwnm3eysll6tfdz8d9gtht97k7tqxsz78n

Why are the two wallets in boldface (change from the above transaction, goes to Alice and receiver of below transaction, should also be Alice's wallet) not identical?

Any hints welcome!

[hosemary]

First of all note that we can't be sure that which of the outputs is the change. We can only make assumptions. It's even possible that the sender has sent fund to two people in a single transaction and there is no change at all.
Second, you can have any number of addresses you want and that's even recommended due to privacy reasons.

[LoyceV]

Second, you can have any number of addresses you want and that's even recommended due to privacy reasons.

Even better: your wallet does this on it's own by sending change to a new address each time.

Don't confuse wallets for addresses: a wallet can hold many different addresses, and each address can receive many individual coins (UTXOs).

[nc50lc]

Any hints welcome!

All your educated guesses on which is change or not is why others called Bitcoin "pseudo-anonymous".
Because even though every transactions are available in public, it's still not easy to tell which is which if the user/wallet do not reuse addresses.

Why are the two wallets in boldface (change from the above transaction, goes to Alice and receiver of below transaction, should also be Alice's wallet) not identical?

Such misconception must have been caused by not having first-hand experience on how wallets create transactions or from using wallets that only use single address.

So, I'd recommend you to test it on a real Bitcoin wallet to better grasp the explanations.
You can make transactions in testnet at no cost (just get some test coins from faucets online), the reference client "Bitcoin Core" (where you can also try RegTest) or "Electrum" supports it.
How to run those clients in testnet/regtest:

• For Bitcoin Core: developer.bitcoin.org/examples/testing.html
• For Electrum: start it with --testnet or --testnet4

[LoyceV]

just get some test coins from faucets online)

If you scan a QR-code (which I just misspelled as QR-coin), you can get some here.

[apogio]

I also have some testnet Bitcoins that I can give: https://bitcointalk.org/index.php?topic=5533904.0

As far as the topic is concerned, I think Loyce and nc50lc covered it well.