Chapter 5 assessment 5

1. Bob wants to ensure that his stateful contract only has a certain number of outputs. Which combination of SIGHASH flags can he use?

   • SIGHASH_ALL

   • SIGHASH_ALL | SIGHASH_ANYONECANPAY

   • Either of the above <-

   • None of the above

2. Alice's transaction has one input with a non-final nSequence value, one output and an nLocktime that is 1000 blocks in the future. What does she need to do to get it into a block as soon as possible?

   • Resubmit it with a new nLocktime but leave the input’s nSequence value the same

   • Resubmit it with a final nSequence value and updated signature - no need to change nLocktime. <-

   • Create a new transaction that is final and has another input attached to pay a much larger fee

   • Send a message to all node operators requesting that her transaction be added to the next block

3. What does SIGHASH_FORKID do?

   • Tells nodes that this transaction is not to be used in a 51% attack

   • It's not a valid SIGHASH and will generate network forks

   • It provides replay protection for transactions so their matching inputs cannot be spent on the BTC network <-

   • It doesn't do anything and is a bug left in the protocol by Satoshi