A user provides me with his wallet pub key as BultinByteString (or Haskell string, fine either way). From that, I need to get the PubKeyHash, but I am not sure how to hash it or if I need to hash it at all.

Then, I need to use it in the PubKeyHash in Ledger.Constraints.MustBeSignedBy in my state machine. Kinda like that:

Constraints.mustBeSignedBy "35dedd2982a03cf39e7dce03c839994ffdec2ec6b04f1cf2d40e61a3"


Constraints.mustBeSignedBy PubKeyHash { getPubKeyHash = "35dedd2982a03cf39e7dce03c839994ffdec2ec6b04f1cf2d40e61a3" }

The problem is when I put some PubKeyHash in the constraint (like above), the compiler spits out 5000 long error starting with:

GHC Core to PLC plugin: E042:Error: Unsupported feature: Use of fromString on type other than builtin strings or bytestrings: Plutus.V1.Ledger.Crypto.PubKeyHash
Context: Compiling expr: Data.String.fromString
                           @ Plutus.V1.Ledger.Crypto.PubKeyHash

Can the string be translated into the PubKeyHash? Can it be somehow fixed? Is it me, or is it a Plutus bug?


Tried new code:

Constraints.mustBeSignedBy $ pubKeyHash (PubKey {
                            getPubKey = LedgerBytes { 
                                    getLedgerBytes = "35dedd2982a03cf39e7dce03c839994ffdec2ec6b04f1cf2d40e61a3" 

Got new error:

 GHC Core to PLC plugin: E042:Error: Unsupported feature: Type constructor: GHC.Prim.Char#
Context: Compiling type: GHC.Prim.Char#
Context: Compiling data constructor type: GHC.Types.C#
Context: Compiling type: GHC.Types.Char
Context: Compiling type: GHC.Base.String
Context: Compiling type: GHC.Base.String
                         -> Plutus.V1.Ledger.Bytes.LedgerBytes
Context: Compiling definition of: Plutus.V1.Ledger.Bytes.$fIsStringLedgerBytes_$cfromString
Context: Compiling expr: Plutus.V1.Ledger.Bytes.$fIsStringLedgerBytes_$cfromString
Context: Compiling expr: Plutus.V1.Ledger.Bytes.$fIsStringLedgerBytes_$cfromString
  • Did you add OverloadedStrings pragma?
    – kindofdev
    Feb 25, 2022 at 18:10
  • Yes, I do have that pragma at the beginning of my file. No other issues with strings occurred in my state machine contract. Feb 25, 2022 at 18:32

1 Answer 1


It's an issue with Plutus core. Even though PubKeyHash is part of IsString type class, we can't use OverloadedStrings mechanism in on-chain code for certain types. Basically, the problem is this:

Unfortunately, due to the technical reasons plutus plugin doesn't support OverloadedStrings with newtypes.

Please, check this issue.


Same thing apply for PubKeyHash and LedgerBytes.

A solution might be to have a parameterized validator script with PubKeyHash. This way, you can build PubkeyHash offchain using OverloadedStrings and pass it to the validator.

  • Thank you! Parameterized validator script with PubKeyHash works like a charm. Indeed a fascinating issue. Feb 25, 2022 at 21:00
  • 1
    @MartinDrozdík You’re welcome. glad to help!
    – kindofdev
    Feb 25, 2022 at 21:30

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