Pass Nonce directly to InvoiceRequestBuilder

When using InvoiceRequestBuilder::deriving_payer_id, the nonce generated
needs to be the same one included in any reply path. This is because the
nonce is used along with the invoice request TLVs to derive a payer id.
While this data is also included in the payer_metadata, including it in
the blinded path would allow reducing the amount of data needed there to
just enough to provide entropy (i.e., 16 bytes). This is more important
for Refund because it can be transmitted via a QR code. But using the
same payer_metadata structure for both InvoiceRequest and Refund would
be beneficial to avoid more code.

Author: jkczyz

lightning/src/ln/channelmanager.rs

@@ -8976,8 +8976,9 @@ where
 		let entropy = &*self.entropy_source;
 		let secp_ctx = &self.secp_ctx;
 
+		let nonce = Nonce::from_entropy_source(entropy);
 		let builder: InvoiceRequestBuilder<DerivedPayerId, secp256k1::All> = offer
-			.request_invoice_deriving_payer_id(expanded_key, entropy, secp_ctx, payment_id)?
+			.request_invoice_deriving_payer_id(expanded_key, nonce, secp_ctx, payment_id)?
 			.into();
 		let builder = builder.chain_hash(self.chain_hash)?;
 

lightning/src/offers/invoice_request.rs

@@ -61,8 +61,6 @@ use bitcoin::blockdata::constants::ChainHash;
 use bitcoin::network::Network;
 use bitcoin::secp256k1::{Keypair, PublicKey, Secp256k1, self};
 use bitcoin::secp256k1::schnorr::Signature;
-use core::ops::Deref;
-use crate::sign::EntropySource;
 use crate::io;
 use crate::blinded_path::BlindedPath;
 use crate::ln::types::PaymentHash;
@@ -171,11 +169,10 @@ macro_rules! invoice_request_explicit_payer_id_builder_methods { ($self: ident,
 	}
 
 	#[cfg_attr(c_bindings, allow(dead_code))]
-	pub(super) fn deriving_metadata<ES: Deref>(
-		offer: &'a Offer, payer_id: PublicKey, expanded_key: &ExpandedKey, entropy_source: ES,
+	pub(super) fn deriving_metadata(
+		offer: &'a Offer, payer_id: PublicKey, expanded_key: &ExpandedKey, nonce: Nonce,
 		payment_id: PaymentId,
-	) -> Self where ES::Target: EntropySource {
-		let nonce = Nonce::from_entropy_source(entropy_source);
+	) -> Self {
 		let payment_id = Some(payment_id);
 		let derivation_material = MetadataMaterial::new(nonce, expanded_key, IV_BYTES, payment_id);
 		let metadata = Metadata::Derived(derivation_material);
@@ -201,11 +198,10 @@ macro_rules! invoice_request_derived_payer_id_builder_methods { (
 	$self: ident, $self_type: ty, $secp_context: ty
 ) => {
 	#[cfg_attr(c_bindings, allow(dead_code))]
-	pub(super) fn deriving_payer_id<ES: Deref>(
-		offer: &'a Offer, expanded_key: &ExpandedKey, entropy_source: ES,
+	pub(super) fn deriving_payer_id(
+		offer: &'a Offer, expanded_key: &ExpandedKey, nonce: Nonce,
 		secp_ctx: &'b Secp256k1<$secp_context>, payment_id: PaymentId
-	) -> Self where ES::Target: EntropySource {
-		let nonce = Nonce::from_entropy_source(entropy_source);
+	) -> Self {
 		let payment_id = Some(payment_id);
 		let derivation_material = MetadataMaterial::new(nonce, expanded_key, IV_BYTES, payment_id);
 		let metadata = Metadata::DerivedSigningPubkey(derivation_material);
@@ -1403,14 +1399,15 @@ mod tests {
 		let payer_id = payer_pubkey();
 		let expanded_key = ExpandedKey::new(&KeyMaterial([42; 32]));
 		let entropy = FixedEntropy {};
+		let nonce = Nonce::from_entropy_source(&entropy);
 		let secp_ctx = Secp256k1::new();
 		let payment_id = PaymentId([1; 32]);
 
 		let offer = OfferBuilder::new(recipient_pubkey())
 			.amount_msats(1000)
 			.build().unwrap();
 		let invoice_request = offer
-			.request_invoice_deriving_metadata(payer_id, &expanded_key, &entropy, payment_id)
+			.request_invoice_deriving_metadata(payer_id, &expanded_key, nonce, payment_id)
 			.unwrap()
 			.build().unwrap()
 			.sign(payer_sign).unwrap();
@@ -1476,14 +1473,15 @@ mod tests {
 	fn builds_invoice_request_with_derived_payer_id() {
 		let expanded_key = ExpandedKey::new(&KeyMaterial([42; 32]));
 		let entropy = FixedEntropy {};
+		let nonce = Nonce::from_entropy_source(&entropy);
 		let secp_ctx = Secp256k1::new();
 		let payment_id = PaymentId([1; 32]);
 
 		let offer = OfferBuilder::new(recipient_pubkey())
 			.amount_msats(1000)
 			.build().unwrap();
 		let invoice_request = offer
-			.request_invoice_deriving_payer_id(&expanded_key, &entropy, &secp_ctx, payment_id)
+			.request_invoice_deriving_payer_id(&expanded_key, nonce, &secp_ctx, payment_id)
 			.unwrap()
 			.build_and_sign()
 			.unwrap();

lightning/src/offers/offer.rs

@@ -82,10 +82,8 @@ use bitcoin::network::Network;
 use bitcoin::secp256k1::{Keypair, PublicKey, Secp256k1, self};
 use core::hash::{Hash, Hasher};
 use core::num::NonZeroU64;
-use core::ops::Deref;
 use core::str::FromStr;
 use core::time::Duration;
-use crate::sign::EntropySource;
 use crate::io;
 use crate::blinded_path::BlindedPath;
 use crate::ln::channelmanager::PaymentId;
@@ -699,25 +697,22 @@ macro_rules! request_invoice_derived_payer_id { ($self: ident, $builder: ty) =>
 	/// [`Bolt12Invoice::verify`]: crate::offers::invoice::Bolt12Invoice::verify
 	/// [`ExpandedKey`]: crate::ln::inbound_payment::ExpandedKey
 	pub fn request_invoice_deriving_payer_id<
-		'a, 'b, ES: Deref,
+		'a, 'b,
 		#[cfg(not(c_bindings))]
 		T: secp256k1::Signing
 	>(
-		&'a $self, expanded_key: &ExpandedKey, entropy_source: ES,
+		&'a $self, expanded_key: &ExpandedKey, nonce: Nonce,
 		#[cfg(not(c_bindings))]
 		secp_ctx: &'b Secp256k1<T>,
 		#[cfg(c_bindings)]
 		secp_ctx: &'b Secp256k1<secp256k1::All>,
 		payment_id: PaymentId
-	) -> Result<$builder, Bolt12SemanticError>
-	where
-		ES::Target: EntropySource,
-	{
+	) -> Result<$builder, Bolt12SemanticError> {
 		if $self.offer_features().requires_unknown_bits() {
 			return Err(Bolt12SemanticError::UnknownRequiredFeatures);
 		}
 
-		Ok(<$builder>::deriving_payer_id($self, expanded_key, entropy_source, secp_ctx, payment_id))
+		Ok(<$builder>::deriving_payer_id($self, expanded_key, nonce, secp_ctx, payment_id))
 	}
 } }
 
@@ -728,18 +723,15 @@ macro_rules! request_invoice_explicit_payer_id { ($self: ident, $builder: ty) =>
 	/// Useful for recurring payments using the same `payer_id` with different invoices.
 	///
 	/// [`InvoiceRequest::payer_id`]: crate::offers::invoice_request::InvoiceRequest::payer_id
-	pub fn request_invoice_deriving_metadata<ES: Deref>(
-		&$self, payer_id: PublicKey, expanded_key: &ExpandedKey, entropy_source: ES,
+	pub fn request_invoice_deriving_metadata(
+		&$self, payer_id: PublicKey, expanded_key: &ExpandedKey, nonce: Nonce,
 		payment_id: PaymentId
-	) -> Result<$builder, Bolt12SemanticError>
-	where
-		ES::Target: EntropySource,
-	{
+	) -> Result<$builder, Bolt12SemanticError> {
 		if $self.offer_features().requires_unknown_bits() {
 			return Err(Bolt12SemanticError::UnknownRequiredFeatures);
 		}
 
-		Ok(<$builder>::deriving_metadata($self, payer_id, expanded_key, entropy_source, payment_id))
+		Ok(<$builder>::deriving_metadata($self, payer_id, expanded_key, nonce, payment_id))
 	}
 
 	/// Creates an [`InvoiceRequestBuilder`] for the offer with the given `metadata` and `payer_id`,