获取离线比特币交易ID，链接多个离线交易

Question

let's say i create a valid transaction (offline without sending it, such as like this: http://brainwallet.org/#tx . let's call this " A "

a)before having sent A, can i get the transaction ID of A?

b)I wish to create a new offline Transaction (called B ), using the outputs from A as inputs for B.Still, A has not been sent to the bitcoin network. Is this possible?

c) if part b) is possible, and I send A, then immediately send B to the bitcoin network. what would happen?

Answer 1

There is no transaction ID in the Bitcoin protocol but a transaction Hash. To make it more clear you need to understand that a transaction has an input and an output.

• The input is composed of the hash of the previous transaction and the signature script that will prove you are the owner of the coins. As you can note there is no input amount because the entire provision of the address will be spend. The change will be send back to you in the transaction output.

• The output is composed of an amount and a signature script. In this case the signature script give the condition that need to be filled to unlock the coins.

So yes you can create B without A has been sent to the network.

What will happen if you send A and B at the same time? Transaction A will be done for sure. The after at least 3 new blocks B will probably be done too but this is not 100% sure because Miners will probably drop B from their memory until A is not spend.

You can get more details about transactions here: https://en.bitcoin.it/wiki/Transactions

and about transaction scripts here: https://en.bitcoin.it/wiki/Script

Answer 2

What you have to remember before doing such things as creating new transactions depending on another unconfirmed (or even offline) transactions is that your transaction A hash (id) could change during mining process.

So, you could send all of your A and B transactions to the network at any time, but there are several options:

1. Transaction A will be included in the next block and confirmed, so when transaction B will included in the next block and everything will be ok.
2. Your transaction A will change it's hash during mining process (see Transaction Malleability) and be included in the next block with different hash (id). In that case your transaction B (which depends on offline calculated hash of transaction A, which is not valid anymore) will never be accepted by the network.