Allowing for a weaker on-chain constraint. Week 05 Homework 2

Question

In HW 2 of Week 5, we need to write a script that mints a token with empty ByteString. The minting policy code on the on-chain part (mkPolicy) could ensure that the token name is empty by defining

    checkMintedAmount :: Bool
    checkMintedAmount = case flattenValue (txInfoMint info) of
      [(_, tn, amt)] -> tn == (TokenName emptyByteString) && amt == 1
      _              -> False

I claim that that the weaker constraint

    checkMintedAmount :: Bool
    checkMintedAmount = case flattenValue (txInfoMint info) of
      [(_, _, amt)] -> amt == 1
      _             -> False

is good enough, since the off-chain part of the code will make sure that the token name is the empty string. I ran the experiment and it seems to work.

Generalizing, it seems that the constraints on the on-chain script can be less stringent than the off-chain constraints if the transaction is going to be initiated by the wallet that owns the UTxO where the script resides. Is this claim correct?

Answer 1

This question was answered by Lars during the Q&A.

In summary, you can't rely on an attacker using your offchain code. An attacker could write their own off chain code that uses a non empty Token name.

Perhaps if you are sure that you are the only person able to use the minting policy (eg you check that the transaction is signed by a specific user), you could make such assumptions.