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Quote from: Terikan
So someone who wants to own Bitcoin gets an address and a private key. What generates these, and how are they transmitted? Are they generated on the user's own computer using the client after they've downloaded the blockchain? Do you need to have a bitcoin in an address for it to exist or can it be created empty?
I guess your wallet (means: bitcoind) generates the address and corresponding private key. It doesn't matter whether the blockchain has already been downloaded or not. Although, as I just think about it, I don't know if that means there is a risk that the same private key/address pair is generated twice by different wallets. Might be theoretically possible but in practice very unlikely.Quote from: Terikan
If the software can create an address and private key, what stops someone from modifying the software to create address/key pairs that don't yet exist, but not add them to the blockchain, so that when one of the addresses is actually created via transaction, they will already have the private key to go with it? Is the key randomly chosen first, then address generated from that, or the reverse, or neither?
There are so many possible private key/address pairs that this is like guessing a very long password. Theoretically possible, but practically not reachable with current hardware resources.Private key and address belong to each other, so I think they can only be generated at the same time. This has something to do with several very big prime numbers, but here my knowledge stops.
Quote from: Terikan
So you send your sig with your address to other nodes when sending bitcoins. Assuming address still has bitcoins on it after the transaction, what prevents using the same signature to spend more coins from that address? Does the private key change, does the sig generator use more than just address/key to generate sig? If so what?
"Signature" means you encrypt something with your private key, which means that it can only be decrypted by the corresponding public key (I think this is the address). So, anyone who is able to decrypt the transaction with the public key can be sure it was encrypted with the private key, which should be at some safe place only you can reach. I don't know how it really is, but there must be some unique details in every transaction (e.g. the current timestamp), making it impossible to just copy the encrypted one and add it again to the blockchain.Hope this helped.
