Move inbound_payment module into its own file

As part of preparing to expose some of its methods as pub for ChannelManager-less
phantom invoice generation.

Pure code move of the module + the addition of module-level documentation

Author: valentinewallace

lightning/src/ln/channelmanager.rs

@@ -40,7 +40,7 @@ use chain::channelmonitor::{ChannelMonitor, ChannelMonitorUpdate, ChannelMonitor
 use chain::transaction::{OutPoint, TransactionData};
 // Since this struct is returned in `list_channels` methods, expose it here in case users want to
 // construct one themselves.
-use ln::{PaymentHash, PaymentPreimage, PaymentSecret};
+use ln::{inbound_payment, PaymentHash, PaymentPreimage, PaymentSecret};
 use ln::channel::{Channel, ChannelError, ChannelUpdateStatus, UpdateFulfillCommitFetch};
 use ln::features::{InitFeatures, NodeFeatures};
 use routing::router::{PaymentParameters, Route, RouteHop, RoutePath, RouteParameters};
@@ -70,276 +70,6 @@ use core::ops::Deref;
 #[cfg(any(test, feature = "std"))]
 use std::time::Instant;
 
-mod inbound_payment {
-	use alloc::string::ToString;
-	use bitcoin::hashes::{Hash, HashEngine};
-	use bitcoin::hashes::cmp::fixed_time_eq;
-	use bitcoin::hashes::hmac::{Hmac, HmacEngine};
-	use bitcoin::hashes::sha256::Hash as Sha256;
-	use chain::keysinterface::{KeyMaterial, KeysInterface, Sign};
-	use ln::{PaymentHash, PaymentPreimage, PaymentSecret};
-	use ln::channelmanager::APIError;
-	use ln::msgs;
-	use ln::msgs::MAX_VALUE_MSAT;
-	use util::chacha20::ChaCha20;
-	use util::crypto::hkdf_extract_expand_thrice;
-	use util::logger::Logger;
-
-	use core::convert::TryInto;
-	use core::ops::Deref;
-
-	const IV_LEN: usize = 16;
-	const METADATA_LEN: usize = 16;
-	const METADATA_KEY_LEN: usize = 32;
-	const AMT_MSAT_LEN: usize = 8;
-	// Used to shift the payment type bits to take up the top 3 bits of the metadata bytes, or to
-	// retrieve said payment type bits.
-	const METHOD_TYPE_OFFSET: usize = 5;
-
-	/// A set of keys that were HKDF-expanded from an initial call to
-	/// [`KeysInterface::get_inbound_payment_key_material`].
-	///
-	/// [`KeysInterface::get_inbound_payment_key_material`]: crate::chain::keysinterface::KeysInterface::get_inbound_payment_key_material
-	pub(super) struct ExpandedKey {
-		/// The key used to encrypt the bytes containing the payment metadata (i.e. the amount and
-		/// expiry, included for payment verification on decryption).
-		metadata_key: [u8; 32],
-		/// The key used to authenticate an LDK-provided payment hash and metadata as previously
-		/// registered with LDK.
-		ldk_pmt_hash_key: [u8; 32],
-		/// The key used to authenticate a user-provided payment hash and metadata as previously
-		/// registered with LDK.
-		user_pmt_hash_key: [u8; 32],
-	}
-
-	impl ExpandedKey {
-		pub(super) fn new(key_material: &KeyMaterial) -> ExpandedKey {
-			let (metadata_key, ldk_pmt_hash_key, user_pmt_hash_key) =
-				hkdf_extract_expand_thrice(b"LDK Inbound Payment Key Expansion", &key_material.0);
-			Self {
-				metadata_key,
-				ldk_pmt_hash_key,
-				user_pmt_hash_key,
-			}
-		}
-	}
-
-	enum Method {
-		LdkPaymentHash = 0,
-		UserPaymentHash = 1,
-	}
-
-	impl Method {
-		fn from_bits(bits: u8) -> Result<Method, u8> {
-			match bits {
-				bits if bits == Method::LdkPaymentHash as u8 => Ok(Method::LdkPaymentHash),
-				bits if bits == Method::UserPaymentHash as u8 => Ok(Method::UserPaymentHash),
-				unknown => Err(unknown),
-			}
-		}
-	}
-
-	pub(super) fn create<Signer: Sign, K: Deref>(keys: &ExpandedKey, min_value_msat: Option<u64>, invoice_expiry_delta_secs: u32, keys_manager: &K, highest_seen_timestamp: u64) -> Result<(PaymentHash, PaymentSecret), ()>
-		where K::Target: KeysInterface<Signer = Signer>
-	{
-		let metadata_bytes = construct_metadata_bytes(min_value_msat, Method::LdkPaymentHash, invoice_expiry_delta_secs, highest_seen_timestamp)?;
-
-		let mut iv_bytes = [0 as u8; IV_LEN];
-		let rand_bytes = keys_manager.get_secure_random_bytes();
-		iv_bytes.copy_from_slice(&rand_bytes[..IV_LEN]);
-
-		let mut hmac = HmacEngine::<Sha256>::new(&keys.ldk_pmt_hash_key);
-		hmac.input(&iv_bytes);
-		hmac.input(&metadata_bytes);
-		let payment_preimage_bytes = Hmac::from_engine(hmac).into_inner();
-
-		let ldk_pmt_hash = PaymentHash(Sha256::hash(&payment_preimage_bytes).into_inner());
-		let payment_secret = construct_payment_secret(&iv_bytes, &metadata_bytes, &keys.metadata_key);
-		Ok((ldk_pmt_hash, payment_secret))
-	}
-
-	pub(super) fn create_from_hash(keys: &ExpandedKey, min_value_msat: Option<u64>, payment_hash: PaymentHash, invoice_expiry_delta_secs: u32, highest_seen_timestamp: u64) -> Result<PaymentSecret, ()> {
-		let metadata_bytes = construct_metadata_bytes(min_value_msat, Method::UserPaymentHash, invoice_expiry_delta_secs, highest_seen_timestamp)?;
-
-		let mut hmac = HmacEngine::<Sha256>::new(&keys.user_pmt_hash_key);
-		hmac.input(&metadata_bytes);
-		hmac.input(&payment_hash.0);
-		let hmac_bytes = Hmac::from_engine(hmac).into_inner();
-
-		let mut iv_bytes = [0 as u8; IV_LEN];
-		iv_bytes.copy_from_slice(&hmac_bytes[..IV_LEN]);
-
-		Ok(construct_payment_secret(&iv_bytes, &metadata_bytes, &keys.metadata_key))
-	}
-
-	fn construct_metadata_bytes(min_value_msat: Option<u64>, payment_type: Method, invoice_expiry_delta_secs: u32, highest_seen_timestamp: u64) -> Result<[u8; METADATA_LEN], ()> {
-		if min_value_msat.is_some() && min_value_msat.unwrap() > MAX_VALUE_MSAT {
-			return Err(());
-		}
-
-		let mut min_amt_msat_bytes: [u8; AMT_MSAT_LEN] = match min_value_msat {
-			Some(amt) => amt.to_be_bytes(),
-			None => [0; AMT_MSAT_LEN],
-		};
-		min_amt_msat_bytes[0] |= (payment_type as u8) << METHOD_TYPE_OFFSET;
-
-		// We assume that highest_seen_timestamp is pretty close to the current time - it's updated when
-		// we receive a new block with the maximum time we've seen in a header. It should never be more
-		// than two hours in the future.  Thus, we add two hours here as a buffer to ensure we
-		// absolutely never fail a payment too early.
-		// Note that we assume that received blocks have reasonably up-to-date timestamps.
-		let expiry_bytes = (highest_seen_timestamp + invoice_expiry_delta_secs as u64 + 7200).to_be_bytes();
-
-		let mut metadata_bytes: [u8; METADATA_LEN] = [0; METADATA_LEN];
-		metadata_bytes[..AMT_MSAT_LEN].copy_from_slice(&min_amt_msat_bytes);
-		metadata_bytes[AMT_MSAT_LEN..].copy_from_slice(&expiry_bytes);
-
-		Ok(metadata_bytes)
-	}
-
-	fn construct_payment_secret(iv_bytes: &[u8; IV_LEN], metadata_bytes: &[u8; METADATA_LEN], metadata_key: &[u8; METADATA_KEY_LEN]) -> PaymentSecret {
-		let mut payment_secret_bytes: [u8; 32] = [0; 32];
-		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];
-		}
-		PaymentSecret(payment_secret_bytes)
-	}
-
-	/// Check that an inbound payment's `payment_data` field is sane.
-	///
-	/// LDK does not store any data for pending inbound payments. Instead, we construct our payment
-	/// secret (and, if supplied by LDK, our payment preimage) to include encrypted metadata about the
-	/// payment.
-	///
-	/// The metadata is constructed as:
-	///   payment method (3 bits) || payment amount (8 bytes - 3 bits) || expiry (8 bytes)
-	/// and encrypted using a key derived from [`KeysInterface::get_inbound_payment_key_material`].
-	///
-	/// Then on payment receipt, we verify in this method that the payment preimage and payment secret
-	/// match what was constructed.
-	///
-	/// [`create_inbound_payment`] and [`create_inbound_payment_for_hash`] are called by the user to
-	/// construct the payment secret and/or payment hash that this method is verifying. If the former
-	/// method is called, then the payment method bits mentioned above are represented internally as
-	/// [`Method::LdkPaymentHash`]. If the latter, [`Method::UserPaymentHash`].
-	///
-	/// For the former method, the payment preimage is constructed as an HMAC of payment metadata and
-	/// random bytes. Because the payment secret is also encoded with these random bytes and metadata
-	/// (with the metadata encrypted with a block cipher), we're able to authenticate the preimage on
-	/// payment receipt.
-	///
-	/// For the latter, the payment secret instead contains an HMAC of the user-provided payment hash
-	/// and payment metadata (encrypted with a block cipher), allowing us to authenticate the payment
-	/// hash and metadata on payment receipt.
-	///
-	/// See [`ExpandedKey`] docs for more info on the individual keys used.
-	///
-	/// [`KeysInterface::get_inbound_payment_key_material`]: crate::chain::keysinterface::KeysInterface::get_inbound_payment_key_material
-	/// [`create_inbound_payment`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment
-	/// [`create_inbound_payment_for_hash`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment_for_hash
-	pub(super) fn verify<L: Deref>(payment_hash: PaymentHash, payment_data: msgs::FinalOnionHopData, highest_seen_timestamp: u64, keys: &ExpandedKey, logger: &L) -> Result<Option<PaymentPreimage>, ()>
-		where L::Target: Logger
-	{
-		let (iv_bytes, metadata_bytes) = decrypt_metadata(payment_data.payment_secret, keys);
-
-		let payment_type_res = Method::from_bits((metadata_bytes[0] & 0b1110_0000) >> METHOD_TYPE_OFFSET);
-		let mut amt_msat_bytes = [0; AMT_MSAT_LEN];
-		amt_msat_bytes.copy_from_slice(&metadata_bytes[..AMT_MSAT_LEN]);
-		// Zero out the bits reserved to indicate the payment type.
-		amt_msat_bytes[0] &= 0b00011111;
-		let min_amt_msat: u64 = u64::from_be_bytes(amt_msat_bytes.into());
-		let expiry = u64::from_be_bytes(metadata_bytes[AMT_MSAT_LEN..].try_into().unwrap());
-
-		// Make sure to check to check the HMAC before doing the other checks below, to mitigate timing
-		// attacks.
-		let mut payment_preimage = None;
-		match payment_type_res {
-			Ok(Method::UserPaymentHash) => {
-				let mut hmac = HmacEngine::<Sha256>::new(&keys.user_pmt_hash_key);
-				hmac.input(&metadata_bytes[..]);
-				hmac.input(&payment_hash.0);
-				if !fixed_time_eq(&iv_bytes, &Hmac::from_engine(hmac).into_inner().split_at_mut(IV_LEN).0) {
-					log_trace!(logger, "Failing HTLC with user-generated payment_hash {}: unexpected payment_secret", log_bytes!(payment_hash.0));
-					return Err(())
-				}
-			},
-			Ok(Method::LdkPaymentHash) => {
-				match derive_ldk_payment_preimage(payment_hash, &iv_bytes, &metadata_bytes, keys) {
-					Ok(preimage) => payment_preimage = Some(preimage),
-					Err(bad_preimage_bytes) => {
-						log_trace!(logger, "Failing HTLC with payment_hash {} due to mismatching preimage {}", log_bytes!(payment_hash.0), log_bytes!(bad_preimage_bytes));
-						return Err(())
-					}
-				}
-			},
-			Err(unknown_bits) => {
-				log_trace!(logger, "Failing HTLC with payment hash {} due to unknown payment type {}", log_bytes!(payment_hash.0), unknown_bits);
-				return Err(());
-			}
-		}
-
-		if payment_data.total_msat < min_amt_msat {
-			log_trace!(logger, "Failing HTLC with payment_hash {} due to total_msat {} being less than the minimum amount of {} msat", log_bytes!(payment_hash.0), payment_data.total_msat, min_amt_msat);
-			return Err(())
-		}
-
-		if expiry < highest_seen_timestamp {
-			log_trace!(logger, "Failing HTLC with payment_hash {}: expired payment", log_bytes!(payment_hash.0));
-			return Err(())
-		}
-
-		Ok(payment_preimage)
-	}
-
-	pub(super) fn get_payment_preimage(payment_hash: PaymentHash, payment_secret: PaymentSecret, keys: &ExpandedKey) -> Result<PaymentPreimage, APIError> {
-		let (iv_bytes, metadata_bytes) = decrypt_metadata(payment_secret, keys);
-
-		match Method::from_bits((metadata_bytes[0] & 0b1110_0000) >> METHOD_TYPE_OFFSET) {
-			Ok(Method::LdkPaymentHash) => {
-				derive_ldk_payment_preimage(payment_hash, &iv_bytes, &metadata_bytes, keys)
-					.map_err(|bad_preimage_bytes| APIError::APIMisuseError {
-						err: format!("Payment hash {} did not match decoded preimage {}", log_bytes!(payment_hash.0), log_bytes!(bad_preimage_bytes))
-					})
-			},
-			Ok(Method::UserPaymentHash) => Err(APIError::APIMisuseError {
-				err: "Expected payment type to be LdkPaymentHash, instead got UserPaymentHash".to_string()
-			}),
-			Err(other) => Err(APIError::APIMisuseError { err: format!("Unknown payment type: {}", other) }),
-		}
-	}
-
-	fn decrypt_metadata(payment_secret: PaymentSecret, keys: &ExpandedKey) -> ([u8; IV_LEN], [u8; METADATA_LEN]) {
-		let mut iv_bytes = [0; IV_LEN];
-		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];
-		}
-
-		(iv_bytes, metadata_bytes)
-	}
-
-	// Errors if the payment preimage doesn't match `payment_hash`. Returns the bad preimage bytes in
-	// this case.
-	fn derive_ldk_payment_preimage(payment_hash: PaymentHash, iv_bytes: &[u8; IV_LEN], metadata_bytes: &[u8; METADATA_LEN], keys: &ExpandedKey) -> Result<PaymentPreimage, [u8; 32]> {
-		let mut hmac = HmacEngine::<Sha256>::new(&keys.ldk_pmt_hash_key);
-		hmac.input(iv_bytes);
-		hmac.input(metadata_bytes);
-		let decoded_payment_preimage = Hmac::from_engine(hmac).into_inner();
-		if !fixed_time_eq(&payment_hash.0, &Sha256::hash(&decoded_payment_preimage).into_inner()) {
-			return Err(decoded_payment_preimage);
-		}
-		return Ok(PaymentPreimage(decoded_payment_preimage))
-	}
-}
-
 // We hold various information about HTLC relay in the HTLC objects in Channel itself:
 //
 // Upon receipt of an HTLC from a peer, we'll give it a PendingHTLCStatus indicating if it should
@@ -7481,7 +7211,7 @@ mod tests {
 		match inbound_payment::verify(bad_payment_hash, payment_data.clone(), nodes[0].node.highest_seen_timestamp.load(Ordering::Acquire) as u64, &nodes[0].node.inbound_payment_key, &nodes[0].logger) {
 			Ok(_) => panic!("Unexpected ok"),
 			Err(()) => {
-				nodes[0].logger.assert_log_contains("lightning::ln::channelmanager::inbound_payment".to_string(), "Failing HTLC with user-generated payment_hash".to_string(), 1);
+				nodes[0].logger.assert_log_contains("lightning::ln::inbound_payment".to_string(), "Failing HTLC with user-generated payment_hash".to_string(), 1);
 			}
 		}