Meetup question regarding double spends - page 2.

achow101

staff

Activity: 3458

Merit: 6793

Just writing some code

Quote from: calkob on February 25, 2016, 05:11:57 PM

Quote from: Lauda on February 25, 2016, 04:55:16 PM

She can't 'double spend' between blocks. Technically she could but this is really hard to do as soon as the transaction has a single confirmation. Do you mean unconfirmed transactions? You should not generally accept 0-conf transactions unless the amount is negligible or you trust the other party. There are a few known types of attacks in regards to double spends. This image might also be useful for your general understanding.

So if she can't double spend between blocks what is stopping her from doing that? is it the wallet that wont allow her to send more than she has?

The double spends are spending inputs that are already spent. It is entirely possible for her to create 10 transactions that spend the same input and send the Bitcoin to 10 different people. However, the consensus rules allow only one of those transactions to be confirmed and thus committed to permanent history. Any transaction that spend off of the other rejected transactions would forever remain unconfirmed and thus susceptible to being impermanent.

calkob

hero member

Activity: 1106

Merit: 521

Quote from: Lauda on February 25, 2016, 04:55:16 PM

She can't 'double spend' between blocks. Technically she could but this is really hard to do as soon as the transaction has a single confirmation. Do you mean unconfirmed transactions? You should not generally accept 0-conf transactions unless the amount is negligible or you trust the other party. There are a few known types of attacks in regards to double spends. This image might also be useful for your general understanding.

So if she can't double spend between blocks what is stopping her from doing that? is it the wallet that wont allow her to send more than she has?

edit: i am talking about a confirmed 1BTC in her wallet what stops her sending it 10 times. is it the fact that all other nodes know she only has 1BTC?

Lauda

legendary

Activity: 2674

Merit: 2965

Terminated.

She can't 'double spend' between blocks. Technically she could but this is really hard to do as soon as the transaction has a single confirmation. Do you mean unconfirmed transactions? You should not generally accept 0-conf transactions unless the amount is negligible or you trust the other party. There are a few known types of attacks in regards to double spends. This image might also be useful for your general understanding.

calkob

hero member

Activity: 1106

Merit: 521

Last night i was at a local Bitcoin meetup and a question was asked about how does bitcoin stop a double spend between blocks. In other words what stops alice from sending 10BTC to 10 people when she only has 1BTC, during the 10 mins to find a block?

Is it simply the nodes know that she only had 1 and so reject the transaction? The answer that was given wasnt really that good and i think was even more confusing. it actually confused me and i thought i understood this.

Could someone please explain in laymans terms so that i can explain it myself in future Grin

Topic: Meetup question regarding double spends - page 2. (Read 967 times)