Bitcoin Forum

Hey guys,

I know there is no "from" address when we send bitcoins. However, is there any way to prove when B receives btc, it was sent from a particular party? If A and C both claim they sent btc to B with the same amount and B only receives one payment, how do we identify the sender?

What do you mean there is no "from" address? In any block explorer we can "received" and "sent" transactions of any bitcoin address.

If A has to send bitcoins to B then A must be having an address - say A's address is AddressA. Now C has their own address - say AddressC. If they send bitcoins to B then in the blockchain explorer we can see that if the transaction came from A or B by checking the address it came from. Even if amounts were same addresses are different. So there is no chance of ambiguity considering the fact that AddressA is not same as AddressC.
I hope this answered your question.

The only reason "from" is not usually used in the Bitcoin world is because many times wallets send from change addresses or from many different addresses, and not actually from the address the user think he has.

So if he claimed he sent from that address, the merchant wouldn't see it.

You can definitely see the addresses that the Bitcoins were sent from on the blockchain. The actual owner of the address(es) that sent the payment to B could then simply "sign a message" proving that they control the private key for that address and therefore "own" it.

It's the reason why a lot of airdrops and ICOs etc want signed messages when claiming coins/payments... It proves control/ownership of a given address.

You dont directly see from which address you will send your btc from. But after you sent your BTC you can look up your transaction
in a blockexplorer (e.g. blockchain.info). The inputs/outputs  are listed there. To prove you, and not another one, sent this transaction
you could sign a message "I, xxx, payed xxx for xxx. Date: xx:xx:xxxx" from one of these input addresses.

Bitcoin has a cryptographic verification called signing messages.  It allows an entity to verify that they have access to the private key of an address without showing the private key.  You can see how this is done here.

This system has a lot of potential uses, including verifying the owner of accounts on this forum.  When a person's account is hacked, they can prove to an admin that they own the account simply by signing a message with an address that they previously used on this forum.

Since you can see which address sent funds to B and at what time, you can ask A and C to sign a message verifying that they own the address that sent to B.

No... if someone claims he sent from an address A to an address B, a simple lookup of that either address on the blockchain should show if that were true or not. Of course, if you were withdrawing from Online Service X to address B, then you're not really sending anything, Online Service X is.


Yes, you do, provided you are in control of your coins and wallet. You're describing what happens when you use an online service's wallet. You request a withdrawal, and wait for them to perform the transaction on your behalf, providing you the transaction ID.

A good wallet, let's say Electrum, should let you determine exactly which inputs and associated addresses will spend your coins to the receiving address.

You are correct.  Bitcoins transactions do NOT have a "from address".

They DO reference previously received transaction outputs which may OR MAY NOT be able to be converted into an address.  However, due to things such as mixers, coinJoin hosted accounts, multiSig, and non-standard output scripts, you can NOT count on being able to determine who the sender is by looking at the outputs that value was previously received with.

Blockchain explorers all look at the previous outputs where bitcoins were received and try to convert that to an address whenever they can, but they often get it wrong.  They are not a reliable source of that information when trying to handle all the ways someone might pay you.  Various people (Airdrops, ICO's, Signature Campaigns, etc) that don't understand how bitcoin actually works will ask users to "provide their sending address" or "sign a message using their sending address".  This misunderstanding leads to confusion and misunderstandings. These people use tools such as blockchain explorers to trace the inputs back to the outputs that are being referenced. Then they try to convert those outputs to addresses.  Then they assume that the addresses were used to send the bitcoins.  They often get it wrong and either have upset customers or a lot of customer support they have to do to straighten it all out.

This is just one of the reasons that you should use a new address for every transaction.

If you ONLY give your receiving address B to party A, then when you receive bitcoins at address B you know that they arrived on behalf of party A.  Someone else might have sent them, but they sent them there because A asked them to.

Imagine you want to buy something from me...
I give an address to you AND ONLY YOU...
I tell you that I will send you the product you have requested when I have received the proper amount of bitcoins sent to that address...

Once enough bitcoins are received using that address, I don't care who sent them.  I only gave the address to you. You have met your obligation of making the arrangements to have the proper amount of bitcoins sent to the address. I now owe you the promised product.

Thanks DannyHamilton for the explanation.

I was under the assumption that there is a sending adress.

You mention that is a reason to use different adresses all is actually to verify the recipient by just providing this adress once. This is actually a very good way to look at it.

What are the other reasons to rotate through adresses?

Thanks
Y

Its actully simple thatn you think.
Ask a and c to give their transaction id.
That transaction id have a success full destination address of yours is the actual one who pays.
Also if anyone of them cannot send transaction id.
Surely he/she did not paid.

Very interesting read. So you can verify that you received an amount of BTC through a specific address of yours, and because you know who you gave this address to, you know who paid you. That's a good use. Never thought about it in that way.

transaction id will give more clarity about the transaction has been sent or not. If the transaction shows as pending or waiting you should wait until the bitcoin transaction. Now number of confirmation has been increased from 2 to 6. However, transaction will be get confirmed faster than now.
There are many bitcoin explorer in the Google results use one among to check the transactions.