Why transactions with same arguments in one case they have same hash but in another case they have a different one?

Question

These 2 extrinsics :

• 10996284-2
• 10995944-2

have the same

• Sender Account (From)
• Destination Account (To)
• Nonce
• Amount
• Transaction Hash

I would like to know the reason why this happened because I am trying to reproduce the same scenario but unsuccessfully.

While I try to reproduce, I make a test by executing 2 new extrinsics with again all same arguments (sender, destination, nonce, amount)

• 12850640-2
• 12850689-2

but now I get a different txHash.

Answer 1

The transactions from 13u3BwugeQzzD755L7jDV2P81h5vwWveYeTHQMB3BVokkWco have the same hash because they are immortals.

The ones from 16ZbFjyAw1s2xv1bBYBHHGTmbXfokoCE3KYENWL1DDiQAo78 have different hashes because they are mortal.

Assuming that you are using a deterministic signature scheme and since the immortal txs reference the genesis hash, they are the same payload.

Mortal transactions must reference the block hash of their first valid block, so those are of course different.

Our recommendation is to use mortal transactions and one of the reasons is mentioned in our wiki quoted below :

NOTE: If an account is reaped and a user re-funds the account, then they could replay an immortal transaction. Always default to using a mortal extrinsic.

Thank you to the external team that asked the question and presented the examples, to Joe Petrowski for giving a super detailed explanation with screenshots & Iker for reviewing.