Initialize New Accounts with Nonce Equal to Block Number

[shawntabrizi]

There is a well known issue that Substrate accounts which are killed could have their txs replayed if the lifetime is infinite.

To help mitigate this, we want to initialize a user's nonce with the number of the current block.

This means that assuming that an account does on average less than one tx per block, that none of it's transactions could be replayed even if the account was killed.

This can also be used as a mechanism to determine how old an account is (relatively). For example, we could start a democracy vote where only users with nonce lower than the current block number could vote. This means that it would not be possible for someone to create a bunch of new accounts after the vote is announced to then influence the outcome.

It would of course be possible to create a bunch of sleeper accounts initialized with a low nonce, but such activity could be monitored and accounted for before the vote takes place. Anyway, this second half is just an idea...

[kevlu93]

I would be interested in helping out! New to the code base though so would need some pointers to get started.

[xlc]

This helps but immortal tx with nonce of 0 is still going to be replayable

[stale]

Hey, is anyone still working on this? Due to the inactivity this issue has been automatically marked as stale. It will be closed if no further activity occurs. Thank you for your contributions.

[Lohann]

Can I take this one? I just faced this issue trying to figure why two transactions in different blocks have the exactly same hash and signature, block explores rely in the tx_hash as unique transaction identifier.

Tx hash: 0x313da69888b43486a5bf717958d02e7228467fa48654c8bd690fe38b56370113

https://polkascan.io/polkadot/block/7911545
https://polkascan.io/polkadot/block/7854172

[shawntabrizi]

That problem is not the same thing as mentioned in this issue.

A tx hash is literally a hash of the tx input data, and can be the same if the same inputs are used AFAIK.

The unique identifier for a tx is (block number, extrinsic index).

[Lohann]

Correct, they have the same hash because the account reuse the same nonce and call the same extrinsic twice. You can see here that the account 13Z4eAVmUt4we1K623cFgYHMnFSDC4cmuJUrGTuUEbZRuyf3 was reaped and created many times:
https://polkascan.io/polkadot/account/13Z4eAVmUt4we1K623cFgYHMnFSDC4cmuJUrGTuUEbZRuyf3#balance-history

This is very counter intuitive, once in all other blockchain I know the transaction hash is global unique (bitcoin, ethereum, cardano, etc), using block_number + extrinsic_index as unique identifier is not very usual and should be better documented. Also I don't think the block explorers are aware about this issue, if you use polkascan for example and click in the transaction, it will display the same block instead show the tx in different blocks.