Merge pull request #2468 from jkczyz/2023-08-offer-payment-id

Offer outbound payments

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -237,7 +237,12 @@ impl From<&ClaimableHTLC> for events::ClaimedHTLC {
 ///
 /// This is not exported to bindings users as we just use [u8; 32] directly
 #[derive(Hash, Copy, Clone, PartialEq, Eq, Debug)]
-pub struct PaymentId(pub [u8; 32]);
+pub struct PaymentId(pub [u8; Self::LENGTH]);
+
+impl PaymentId {
+	/// Number of bytes in the id.
+	pub const LENGTH: usize = 32;
+}
 
 impl Writeable for PaymentId {
 	fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {

lightning/src/ln/inbound_payment.rs

@@ -19,7 +19,7 @@ use crate::ln::{PaymentHash, PaymentPreimage, PaymentSecret};
 use crate::ln::msgs;
 use crate::ln::msgs::MAX_VALUE_MSAT;
 use crate::util::chacha20::ChaCha20;
-use crate::util::crypto::hkdf_extract_expand_4x;
+use crate::util::crypto::hkdf_extract_expand_5x;
 use crate::util::errors::APIError;
 use crate::util::logger::Logger;
 
@@ -50,27 +50,34 @@ pub struct ExpandedKey {
 	user_pmt_hash_key: [u8; 32],
 	/// The base key used to derive signing keys and authenticate messages for BOLT 12 Offers.
 	offers_base_key: [u8; 32],
+	/// The key used to encrypt message metadata for BOLT 12 Offers.
+	offers_encryption_key: [u8; 32],
 }
 
 impl ExpandedKey {
 	/// Create a  new [`ExpandedKey`] for generating an inbound payment hash and secret.
 	///
 	/// It is recommended to cache this value and not regenerate it for each new inbound payment.
 	pub fn new(key_material: &KeyMaterial) -> ExpandedKey {
-		let (metadata_key, ldk_pmt_hash_key, user_pmt_hash_key, offers_base_key) =
-			hkdf_extract_expand_4x(b"LDK Inbound Payment Key Expansion", &key_material.0);
+		let (
+			metadata_key,
+			ldk_pmt_hash_key,
+			user_pmt_hash_key,
+			offers_base_key,
+			offers_encryption_key,
+		) = hkdf_extract_expand_5x(b"LDK Inbound Payment Key Expansion", &key_material.0);
 		Self {
 			metadata_key,
 			ldk_pmt_hash_key,
 			user_pmt_hash_key,
 			offers_base_key,
+			offers_encryption_key,
 		}
 	}
 
 	/// Returns an [`HmacEngine`] used to construct [`Offer::metadata`].
 	///
 	/// [`Offer::metadata`]: crate::offers::offer::Offer::metadata
-	#[allow(unused)]
 	pub(crate) fn hmac_for_offer(
 		&self, nonce: Nonce, iv_bytes: &[u8; IV_LEN]
 	) -> HmacEngine<Sha256> {
@@ -79,6 +86,13 @@ impl ExpandedKey {
 		hmac.input(&nonce.0);
 		hmac
 	}
+
+	/// Encrypts or decrypts the given `bytes`. Used for data included in an offer message's
+	/// metadata (e.g., payment id).
+	pub(crate) fn crypt_for_offer(&self, mut bytes: [u8; 32], nonce: Nonce) -> [u8; 32] {
+		ChaCha20::encrypt_single_block_in_place(&self.offers_encryption_key, &nonce.0, &mut bytes);
+		bytes
+	}
 }
 
 /// A 128-bit number used only once.
@@ -88,7 +102,6 @@ impl ExpandedKey {
 ///
 /// [`Offer::metadata`]: crate::offers::offer::Offer::metadata
 /// [`Offer::signing_pubkey`]: crate::offers::offer::Offer::signing_pubkey
-#[allow(unused)]
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub(crate) struct Nonce(pub(crate) [u8; Self::LENGTH]);
 
@@ -271,10 +284,9 @@ fn construct_payment_secret(iv_bytes: &[u8; IV_LEN], metadata_bytes: &[u8; METAD
 	let (iv_slice, encrypted_metadata_slice) = payment_secret_bytes.split_at_mut(IV_LEN);
 	iv_slice.copy_from_slice(iv_bytes);
 
-	let chacha_block = ChaCha20::get_single_block(metadata_key, iv_bytes);
-	for i in 0..METADATA_LEN {
-		encrypted_metadata_slice[i] = chacha_block[i] ^ metadata_bytes[i];
-	}
+	ChaCha20::encrypt_single_block(
+		metadata_key, iv_bytes, encrypted_metadata_slice, metadata_bytes
+	);
 	PaymentSecret(payment_secret_bytes)
 }
 
@@ -406,11 +418,10 @@ fn decrypt_metadata(payment_secret: PaymentSecret, keys: &ExpandedKey) -> ([u8;
 	let (iv_slice, encrypted_metadata_bytes) = payment_secret.0.split_at(IV_LEN);
 	iv_bytes.copy_from_slice(iv_slice);
 
-	let chacha_block = ChaCha20::get_single_block(&keys.metadata_key, &iv_bytes);
 	let mut metadata_bytes: [u8; METADATA_LEN] = [0; METADATA_LEN];
-	for i in 0..METADATA_LEN {
-		metadata_bytes[i] = chacha_block[i] ^ encrypted_metadata_bytes[i];
-	}
+	ChaCha20::encrypt_single_block(
+		&keys.metadata_key, &iv_bytes, &mut metadata_bytes, encrypted_metadata_bytes
+	);
 
 	(iv_bytes, metadata_bytes)
 }

lightning/src/offers/invoice.rs

@@ -110,6 +110,7 @@ use core::time::Duration;
 use crate::io;
 use crate::blinded_path::BlindedPath;
 use crate::ln::PaymentHash;
+use crate::ln::channelmanager::PaymentId;
 use crate::ln::features::{BlindedHopFeatures, Bolt12InvoiceFeatures, InvoiceRequestFeatures, OfferFeatures};
 use crate::ln::inbound_payment::ExpandedKey;
 use crate::ln::msgs::DecodeError;
@@ -695,10 +696,11 @@ impl Bolt12Invoice {
 		merkle::message_digest(SIGNATURE_TAG, &self.bytes).as_ref().clone()
 	}
 
-	/// Verifies that the invoice was for a request or refund created using the given key.
+	/// Verifies that the invoice was for a request or refund created using the given key. Returns
+	/// the associated [`PaymentId`] to use when sending the payment.
 	pub fn verify<T: secp256k1::Signing>(
 		&self, key: &ExpandedKey, secp_ctx: &Secp256k1<T>
-	) -> bool {
+	) -> Result<PaymentId, ()> {
 		self.contents.verify(TlvStream::new(&self.bytes), key, secp_ctx)
 	}
 
@@ -947,7 +949,7 @@ impl InvoiceContents {
 
 	fn verify<T: secp256k1::Signing>(
 		&self, tlv_stream: TlvStream<'_>, key: &ExpandedKey, secp_ctx: &Secp256k1<T>
-	) -> bool {
+	) -> Result<PaymentId, ()> {
 		let offer_records = tlv_stream.clone().range(OFFER_TYPES);
 		let invreq_records = tlv_stream.range(INVOICE_REQUEST_TYPES).filter(|record| {
 			match record.r#type {
@@ -967,10 +969,7 @@ impl InvoiceContents {
 			},
 		};
 
-		match signer::verify_metadata(metadata, key, iv_bytes, payer_id, tlv_stream, secp_ctx) {
-			Ok(_) => true,
-			Err(()) => false,
-		}
+		signer::verify_payer_metadata(metadata, key, iv_bytes, payer_id, tlv_stream, secp_ctx)
 	}
 
 	fn derives_keys(&self) -> bool {
@@ -1642,36 +1641,31 @@ mod tests {
 			.build().unwrap()
 			.sign(payer_sign).unwrap();
 
-		if let Err(e) = invoice_request
-			.verify_and_respond_using_derived_keys_no_std(
-				payment_paths(), payment_hash(), now(), &expanded_key, &secp_ctx
-			)
-			.unwrap()
+		if let Err(e) = invoice_request.clone()
+			.verify(&expanded_key, &secp_ctx).unwrap()
+			.respond_using_derived_keys_no_std(payment_paths(), payment_hash(), now()).unwrap()
 			.build_and_sign(&secp_ctx)
 		{
 			panic!("error building invoice: {:?}", e);
 		}
 
 		let expanded_key = ExpandedKey::new(&KeyMaterial([41; 32]));
-		match invoice_request.verify_and_respond_using_derived_keys_no_std(
-			payment_paths(), payment_hash(), now(), &expanded_key, &secp_ctx
-		) {
-			Ok(_) => panic!("expected error"),
-			Err(e) => assert_eq!(e, Bolt12SemanticError::InvalidMetadata),
-		}
+		assert!(invoice_request.verify(&expanded_key, &secp_ctx).is_err());
 
 		let desc = "foo".to_string();
 		let offer = OfferBuilder
 			::deriving_signing_pubkey(desc, node_id, &expanded_key, &entropy, &secp_ctx)
 			.amount_msats(1000)
+			// Omit the path so that node_id is used for the signing pubkey instead of deriving
 			.build().unwrap();
 		let invoice_request = offer.request_invoice(vec![1; 32], payer_pubkey()).unwrap()
 			.build().unwrap()
 			.sign(payer_sign).unwrap();
 
-		match invoice_request.verify_and_respond_using_derived_keys_no_std(
-			payment_paths(), payment_hash(), now(), &expanded_key, &secp_ctx
-		) {
+		match invoice_request
+			.verify(&expanded_key, &secp_ctx).unwrap()
+			.respond_using_derived_keys_no_std(payment_paths(), payment_hash(), now())
+		{
 			Ok(_) => panic!("expected error"),
 			Err(e) => assert_eq!(e, Bolt12SemanticError::InvalidMetadata),
 		}