stop transactions from being able to be duplicated and still being valid

[ethan-xd]

if you duplicate a transaction in the transaction list it will still be treated as valid after remining the block as the amount, from and to are still valid with the signature.

need some sort of unique id that cant be duplicated throughout the transaction list (either incrementing number or random number??)

[ethan-xd]

also duplicating a transaction across blocks is also counted as valid, needs unique identifier across entire blockchain. random number okay or too many odds of clashes?

[ethan-xd]

maybe need transaction timestamp to be less than block timestamp?

[ethan-xd]

UTXO is a better solution