Rename PaymentId hmac creation/verification methods for offers.

We want to specify that these methods are only to be used in an outbound offers
payment context, because we'll be adding similar methods for the outbound async
payments context in upcoming commits.

lightning/src/ln/channelmanager.rs

@@ -427,15 +427,15 @@ impl PaymentId {
 	pub fn hmac_for_offer_payment(
 		&self, nonce: Nonce, expanded_key: &inbound_payment::ExpandedKey,
 	) -> Hmac<Sha256> {
-		signer::hmac_for_payment_id(*self, nonce, expanded_key)
+		signer::hmac_for_offer_payment_id(*self, nonce, expanded_key)
 	}
 
 	/// Authenticates the payment id using an HMAC and a [`Nonce`] taken from an
 	/// [`OffersContext::OutboundPayment`].
-	pub fn verify(
+	pub fn verify_for_offer_payment(
 		&self, hmac: Hmac<Sha256>, nonce: Nonce, expanded_key: &inbound_payment::ExpandedKey,
 	) -> Result<(), ()> {
-		signer::verify_payment_id(*self, hmac, nonce, expanded_key)
+		signer::verify_offer_payment_id(*self, hmac, nonce, expanded_key)
 	}
 }
 
@@ -11052,7 +11052,7 @@ where
 			OffersMessage::StaticInvoice(invoice) => {
 				let payment_id = match context {
 					Some(OffersContext::OutboundPayment { payment_id, nonce, hmac: Some(hmac) }) => {
-						if payment_id.verify(hmac, nonce, expanded_key).is_err() {
+						if payment_id.verify_for_offer_payment(hmac, nonce, expanded_key).is_err() {
 							return None
 						}
 						payment_id
@@ -11073,7 +11073,7 @@ where
 
 				match context {
 					Some(OffersContext::OutboundPayment { payment_id, nonce, hmac: Some(hmac) }) => {
-						if let Ok(()) = payment_id.verify(hmac, nonce, expanded_key) {
+						if let Ok(()) = payment_id.verify_for_offer_payment(hmac, nonce, expanded_key) {
 							self.abandon_payment_with_reason(
 								payment_id, PaymentFailureReason::InvoiceRequestRejected,
 							);

lightning/src/offers/signer.rs

@@ -37,7 +37,7 @@ const WITHOUT_ENCRYPTED_PAYMENT_ID_HMAC_INPUT: &[u8; 16] = &[3; 16];
 const WITH_ENCRYPTED_PAYMENT_ID_HMAC_INPUT: &[u8; 16] = &[4; 16];
 
 // HMAC input for a `PaymentId`. The HMAC is used in `OffersContext::OutboundPayment`.
-const PAYMENT_ID_HMAC_INPUT: &[u8; 16] = &[5; 16];
+const OFFER_PAYMENT_ID_HMAC_INPUT: &[u8; 16] = &[5; 16];
 
 /// Message metadata which possibly is derived from [`MetadataMaterial`] such that it can be
 /// verified.
@@ -395,21 +395,21 @@ fn hmac_for_message<'a>(
 	Ok(hmac)
 }
 
-pub(crate) fn hmac_for_payment_id(
+pub(crate) fn hmac_for_offer_payment_id(
 	payment_id: PaymentId, nonce: Nonce, expanded_key: &ExpandedKey,
 ) -> Hmac<Sha256> {
 	const IV_BYTES: &[u8; IV_LEN] = b"LDK Payment ID ~";
 	let mut hmac = expanded_key.hmac_for_offer();
 	hmac.input(IV_BYTES);
 	hmac.input(&nonce.0);
-	hmac.input(PAYMENT_ID_HMAC_INPUT);
+	hmac.input(OFFER_PAYMENT_ID_HMAC_INPUT);
 	hmac.input(&payment_id.0);
 
 	Hmac::from_engine(hmac)
 }
 
-pub(crate) fn verify_payment_id(
+pub(crate) fn verify_offer_payment_id(
 	payment_id: PaymentId, hmac: Hmac<Sha256>, nonce: Nonce, expanded_key: &ExpandedKey,
 ) -> Result<(), ()> {
-	if hmac_for_payment_id(payment_id, nonce, expanded_key) == hmac { Ok(()) } else { Err(()) }
+	if hmac_for_offer_payment_id(payment_id, nonce, expanded_key) == hmac { Ok(()) } else { Err(()) }
 }