Add signer trait to the `simplicity-core` by ikripaka · Pull Request #58 · BlockstreamResearch/simplicity-contracts

ikripaka · 2026-01-21T12:22:13Z

Signer trait would help in future create easy to use finalization of transactions

KyrylR · 2026-01-22T14:40:00Z

crates/simplicityhl-core/src/signer.rs

+
+    /// Get the dummy keypair used for fee estimation.
+    /// This keypair is deterministic and used only to produce valid transaction structures.
+    #[allow(unused)]


This is weird

clippy warns about it
DummySigner can be used in some tests

Why we are adding private functionality to the crate which intention to provide tools for external crates?

ok, in some case DummySigner can be deleted , because can be unused by others

KyrylR · 2026-01-22T14:41:11Z

crates/simplicityhl-core/src/signer.rs

+    /// Returns a closure that signs a transaction with dummy signatures.
+    ///
+    /// This is used for fee estimation - the transaction needs valid witness data
+    /// to calculate accurate weight/fees, but the actual signatures don't need
+    /// to be cryptographically valid for spending (they just need to be the right size).
+    #[allow(clippy::type_complexity, unused)]
+    pub(crate) fn get_signer_closure() -> impl SignerTrait {
+        |network: SimplicityNetwork, tx: Transaction, utxos: &[TxOut]| {
+            let keypair = Self::get_dummy_keypair();
+            let x_only_public_key = keypair.x_only_public_key().0;
+            let p2pk_program = get_p2pk_program(&x_only_public_key)?;
+            let cmr = p2pk_program.commit().cmr();
+
+            let dummy_address =
+                create_p2tr_address(cmr, &x_only_public_key, network.address_params());
+            let dummy_script_pubkey = dummy_address.script_pubkey();
+
+            let dummy_utxos: Vec<TxOut> = utxos
+                .iter()
+                .map(|utxo: &TxOut| TxOut {
+                    script_pubkey: dummy_script_pubkey.clone(),
+                    ..utxo.clone()
+                })
+                .collect();
+
+            let mut signed_tx = tx;
+
+            for i in 0..signed_tx.input.len() {
+                let signature =
+                    create_p2pk_signature(&signed_tx, &dummy_utxos, &keypair, i, network)?;
+
+                signed_tx = finalize_p2pk_transaction(
+                    signed_tx,
+                    &dummy_utxos,
+                    &x_only_public_key,
+                    &signature,
+                    i,
+                    network,
+                    TrackerLogLevel::None,
+                )?;
+            }
+
+            Ok(signed_tx)
+        }
+    }


The function name and what it actually does is different

That is the DummySigner - the idea was to create type, which would be responsible for signing, which doesn't require valid Keypair for signing.
Due to internal checks of ScriptPubkey we have to manually change owner of utxo.
Yeah, it changes owner of utxo on draft keypair and signs as p2pk utxo.

KyrylR · 2026-01-22T14:42:03Z

crates/simplicityhl-core/src/signer.rs

+pub trait SignerTrait:
+    Fn(SimplicityNetwork, Transaction, &[TxOut]) -> Result<Transaction, ProgramError> + Clone
+{
+}
+
+impl<T> SignerTrait for T where
+    T: Fn(SimplicityNetwork, Transaction, &[TxOut]) -> Result<Transaction, ProgramError> + Clone
+{
+}
+
+#[allow(dead_code)]
+pub trait SignerOnceTrait:
+    FnOnce(SimplicityNetwork, Transaction, &[TxOut]) -> Result<Transaction, ProgramError>
+{
+}
+
+impl<T> SignerOnceTrait for T where
+    T: FnOnce(SimplicityNetwork, Transaction, &[TxOut]) -> Result<Transaction, ProgramError>
+{
+}


Explain the idea pls

For standard finalization, if we need to calculate fees from scratch we must call valid signing function twice.
However if we provide our own values the transaction would be signed only once.

Therefore this traits can be used to bound the invocation of sign functions.
We can use SignerTrait to invoke another function that is bounded by SignerOnceTrait.

since SignerTrait is an Fn, it implements FnOnce by default. This allows us to invoke a function that performs the signing operation only once.

SignerOnceTrait can also be used in external code by users who want to restrict specific traits to sign function that can only be called once.

So the the idea lies in restricting even inner functions to FnOnce even if we receive Fn

KyrylR · 2026-01-23T11:52:41Z

crates/simplicityhl-core/src/signer.rs

+            let dummy_utxos: Vec<TxOut> = utxos
+                .iter()
+                .map(|utxo: &TxOut| TxOut {
+                    script_pubkey: dummy_script_pubkey.clone(),


This looks wrong

ok, exactly in this case I wanted to define DummySigner as draft one, which can be used in any case
by using it wihout script_pubkey is impossible, code would fail

we can redefine it with trait which would give Keypair type to function and sign only with p2pk(lets say P2pkSigner), but in this way we mabe lose flexibilty of creating signature to any utxo
I mean some utxos has to be signed in another way than p2pk

(I've looked through all signing functions and by now we only require p2pk)

So, maybe it makes sense to define DummySigner as P2pkSigner, which would by giving

ok, maybe it makes sense to define signer like this?

pub trait P2PKSigner { fn x_only_public_key() -> XOnlyPublicKey; fn sign_p2pk_utxo(&self, network: SimplicityNetwork, tx: Transaction, utxos: &[TxOut], input_index: usize) -> Result<Transaction, ProgramError>; } pub struct SimpleSigner {} impl P2PKSigner for SimpleSigner { fn sign_p2pk_utxo(&self, network: SimplicityNetwork, tx: Transaction, utxos: &[TxOut], input_index: usize) -> Result<Transaction, ProgramError>{ keypair.sign_schnorr(sighash_all) } }

we would leave Keypair storage on the Wallet or any user implementation and in the same way we'd feed signed bytes into our backend where it is needed

KyrylR · 2026-01-23T11:53:41Z

crates/simplicityhl-core/src/signer.rs

@@ -0,0 +1,92 @@
+use crate::{


It is unclear how it should be used

It should be used together with simplicityhl-core errors and functions

functions is related only to DummySigner, but trait can be used with ProgramError

KyrylR · 2026-01-29T11:10:56Z

I would like to reiterate on the approach, closing the PR for the time being

ikripaka self-assigned this Jan 21, 2026

ikripaka requested a review from KyrylR as a code owner January 21, 2026 12:22

ikripaka changed the title ~~Add signer trait to the simplicity-core~~ Add signer trait to the simplicity-contracts Jan 21, 2026

ikripaka mentioned this pull request Jan 21, 2026

Usage of PartialPset in code #54

Closed

Add signer trait to the simplicity-core

c8ba908

ikripaka force-pushed the feature/signer branch from e74b649 to c8ba908 Compare January 22, 2026 14:39

ikripaka changed the title ~~Add signer trait to the simplicity-contracts~~ Add signer trait to the simplicity-core Jan 22, 2026

KyrylR requested changes Jan 22, 2026

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KyrylR requested changes Jan 23, 2026

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KyrylR closed this Jan 29, 2026

KyrylR deleted the feature/signer branch February 12, 2026 15:53

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ikripaka commented Jan 21, 2026

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KyrylR commented Jan 29, 2026

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