Bitcoin and chains · 15 / 127 · 2 min
Change
A bitcoin payment often sends the rest back to a new address of yours. The new address is not a stranger. It is the change.
The leftover is usually yours. It is still an address, and it still has to be checked.
A worked case
Someone sends bitcoin and panics at a second output. It was change. Another person, the dangerous one, pastes an address from a stranger into the change field. The leftover leaves.
The rest
You spend one coin and the payment is smaller. The leftover is a new output. A wallet usually makes that output an address it also controls.
The scare
A person sees a second address and thinks the coins were stolen. They were split. The danger is the reverse: sending the whole amount to someone else because the change address was not checked.
The leftover is an output
Bitcoin spends come from previous receipts, and they rarely match the amount you meant to pay. The difference is a new output. Wallets usually send that output to a fresh address they control, so the leftover is not sitting on the address you just exposed.
The new address is why a payment can look like two payments. It is also why a field you edit by hand can send the leftover away. The chain records the outputs you signed. It does not label one of them change.
Read it yourself
These links are the record. They are not a recommendation, and they are not instructions. A news story or a court paper can still be wrong about a detail. The check does not change because a famous name is in the story.
Apply the check
Open a question. The line is about this topic. It is not a verdict that anything is safe.
The recipient of whichever output you signed.
Your wallet, if it built the change. You, if you edited it.
The signature. The chain will not guess which output you meant to keep.
Check yourself
Write it in your own words. The course's answer opens after that. Nothing is sent.
After this you can say which output is the payment and which is the change.