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Comment by nwh | Hacker News Reader

Malware aside, it's annoying that people still think Bitcoin payments come "from" an address. It's not something you can rely on or expect in Bitcoin, and certainly shouldn't be used to identify payments by a client. A unique address per payment requested is the proper, expected method.

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I don't really think the malware author cares.

>Malware aside, it's annoying that people still think Bitcoin payments come "from" an address.

Do you mind clarifying?

Sure. You essentially can't rely on a particular wallet sending from an address they know about, or even from an address they can control.

The classic example is of a service using a shared wallet like Coinbase does. Coinbase maintains control of the keys of every piece of Bitcoin their clients own, and they have an external database that contains a record of how much Bitcoin they are holding on behalf of their clients. This allows them to keep the vast majority of the funds offline where they are invulnerable to attack. This system means that the "from" address is likely never correlated to the sender, and they have no control of where they send "from". Relying on a client to provide this information usually ends in disaster, as does sending refunds to an address you were sent "from".

Even for the reference client Bitcoin-QT addresses are disposable and almost never linked. Change from one transaction is sent to an entirely new address which done invisibly from the users perspective. There's more information about that on the wiki, change addresses in themselves are quite confusing.

https://en.bitcoin.it/wiki/Change

For all intents and purposes, they do though. Using as an input that was originally an output sent to an address is practically the same thing as coming from the address itself. It only really breaks down for more complicated transactions.

The problem is that most clients are in control of a ton of addresses. Transactions often will come from a combination of several of the addresses. And the user has no control over which addresses are used. So a user cannot enter what address(es) a transaction will come from before the transaction is sent.

Bitcrypt works around this problem by having the victim enter the address after the transaction is sent. But this also has a problem. The victim can simply go to this page http://blockchain.info/address/1HKCHx1RFhNHuF3NxLviHdrjNFzJb... and watch for when a different victim sends a new transaction to that address. Then the first victim can claim that payment as their own.

The more cryptographic version is to sign a challenge with the private key that allows spending of the bitcoins on that address to prove that you own the address. Or you know, do what most people do and have a unique bitcoin address for each person in order to identify them.

They don't come from an address, they come from a previous transaction.

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