1 // This file is Copyright its original authors, visible in version control
4 // This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
5 // or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
7 // You may not use this file except in accordance with one or both of these
10 //! Utilities to generate inbound payment information in service of invoice creation.
12 use alloc::string::ToString;
13 use bitcoin::hashes::{Hash, HashEngine};
14 use bitcoin::hashes::cmp::fixed_time_eq;
15 use bitcoin::hashes::hmac::{Hmac, HmacEngine};
16 use bitcoin::hashes::sha256::Hash as Sha256;
17 use chain::keysinterface::{KeyMaterial, KeysInterface, Sign};
18 use ln::{PaymentHash, PaymentPreimage, PaymentSecret};
20 use ln::msgs::MAX_VALUE_MSAT;
21 use util::chacha20::ChaCha20;
22 use util::crypto::hkdf_extract_expand_thrice;
23 use util::errors::APIError;
24 use util::logger::Logger;
26 use core::convert::TryInto;
29 const IV_LEN: usize = 16;
30 const METADATA_LEN: usize = 16;
31 const METADATA_KEY_LEN: usize = 32;
32 const AMT_MSAT_LEN: usize = 8;
33 // Used to shift the payment type bits to take up the top 3 bits of the metadata bytes, or to
34 // retrieve said payment type bits.
35 const METHOD_TYPE_OFFSET: usize = 5;
37 /// A set of keys that were HKDF-expanded from an initial call to
38 /// [`KeysInterface::get_inbound_payment_key_material`].
40 /// [`KeysInterface::get_inbound_payment_key_material`]: crate::chain::keysinterface::KeysInterface::get_inbound_payment_key_material
41 pub(super) struct ExpandedKey {
42 /// The key used to encrypt the bytes containing the payment metadata (i.e. the amount and
43 /// expiry, included for payment verification on decryption).
44 metadata_key: [u8; 32],
45 /// The key used to authenticate an LDK-provided payment hash and metadata as previously
46 /// registered with LDK.
47 ldk_pmt_hash_key: [u8; 32],
48 /// The key used to authenticate a user-provided payment hash and metadata as previously
49 /// registered with LDK.
50 user_pmt_hash_key: [u8; 32],
54 pub(super) fn new(key_material: &KeyMaterial) -> ExpandedKey {
55 let (metadata_key, ldk_pmt_hash_key, user_pmt_hash_key) =
56 hkdf_extract_expand_thrice(b"LDK Inbound Payment Key Expansion", &key_material.0);
71 fn from_bits(bits: u8) -> Result<Method, u8> {
73 bits if bits == Method::LdkPaymentHash as u8 => Ok(Method::LdkPaymentHash),
74 bits if bits == Method::UserPaymentHash as u8 => Ok(Method::UserPaymentHash),
75 unknown => Err(unknown),
80 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), ()>
81 where K::Target: KeysInterface<Signer = Signer>
83 let metadata_bytes = construct_metadata_bytes(min_value_msat, Method::LdkPaymentHash, invoice_expiry_delta_secs, highest_seen_timestamp)?;
85 let mut iv_bytes = [0 as u8; IV_LEN];
86 let rand_bytes = keys_manager.get_secure_random_bytes();
87 iv_bytes.copy_from_slice(&rand_bytes[..IV_LEN]);
89 let mut hmac = HmacEngine::<Sha256>::new(&keys.ldk_pmt_hash_key);
90 hmac.input(&iv_bytes);
91 hmac.input(&metadata_bytes);
92 let payment_preimage_bytes = Hmac::from_engine(hmac).into_inner();
94 let ldk_pmt_hash = PaymentHash(Sha256::hash(&payment_preimage_bytes).into_inner());
95 let payment_secret = construct_payment_secret(&iv_bytes, &metadata_bytes, &keys.metadata_key);
96 Ok((ldk_pmt_hash, payment_secret))
99 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, ()> {
100 let metadata_bytes = construct_metadata_bytes(min_value_msat, Method::UserPaymentHash, invoice_expiry_delta_secs, highest_seen_timestamp)?;
102 let mut hmac = HmacEngine::<Sha256>::new(&keys.user_pmt_hash_key);
103 hmac.input(&metadata_bytes);
104 hmac.input(&payment_hash.0);
105 let hmac_bytes = Hmac::from_engine(hmac).into_inner();
107 let mut iv_bytes = [0 as u8; IV_LEN];
108 iv_bytes.copy_from_slice(&hmac_bytes[..IV_LEN]);
110 Ok(construct_payment_secret(&iv_bytes, &metadata_bytes, &keys.metadata_key))
113 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], ()> {
114 if min_value_msat.is_some() && min_value_msat.unwrap() > MAX_VALUE_MSAT {
118 let mut min_amt_msat_bytes: [u8; AMT_MSAT_LEN] = match min_value_msat {
119 Some(amt) => amt.to_be_bytes(),
120 None => [0; AMT_MSAT_LEN],
122 min_amt_msat_bytes[0] |= (payment_type as u8) << METHOD_TYPE_OFFSET;
124 // We assume that highest_seen_timestamp is pretty close to the current time - it's updated when
125 // we receive a new block with the maximum time we've seen in a header. It should never be more
126 // than two hours in the future. Thus, we add two hours here as a buffer to ensure we
127 // absolutely never fail a payment too early.
128 // Note that we assume that received blocks have reasonably up-to-date timestamps.
129 let expiry_bytes = (highest_seen_timestamp + invoice_expiry_delta_secs as u64 + 7200).to_be_bytes();
131 let mut metadata_bytes: [u8; METADATA_LEN] = [0; METADATA_LEN];
132 metadata_bytes[..AMT_MSAT_LEN].copy_from_slice(&min_amt_msat_bytes);
133 metadata_bytes[AMT_MSAT_LEN..].copy_from_slice(&expiry_bytes);
138 fn construct_payment_secret(iv_bytes: &[u8; IV_LEN], metadata_bytes: &[u8; METADATA_LEN], metadata_key: &[u8; METADATA_KEY_LEN]) -> PaymentSecret {
139 let mut payment_secret_bytes: [u8; 32] = [0; 32];
140 let (iv_slice, encrypted_metadata_slice) = payment_secret_bytes.split_at_mut(IV_LEN);
141 iv_slice.copy_from_slice(iv_bytes);
143 let chacha_block = ChaCha20::get_single_block(metadata_key, iv_bytes);
144 for i in 0..METADATA_LEN {
145 encrypted_metadata_slice[i] = chacha_block[i] ^ metadata_bytes[i];
147 PaymentSecret(payment_secret_bytes)
150 /// Check that an inbound payment's `payment_data` field is sane.
152 /// LDK does not store any data for pending inbound payments. Instead, we construct our payment
153 /// secret (and, if supplied by LDK, our payment preimage) to include encrypted metadata about the
156 /// The metadata is constructed as:
157 /// payment method (3 bits) || payment amount (8 bytes - 3 bits) || expiry (8 bytes)
158 /// and encrypted using a key derived from [`KeysInterface::get_inbound_payment_key_material`].
160 /// Then on payment receipt, we verify in this method that the payment preimage and payment secret
161 /// match what was constructed.
163 /// [`create_inbound_payment`] and [`create_inbound_payment_for_hash`] are called by the user to
164 /// construct the payment secret and/or payment hash that this method is verifying. If the former
165 /// method is called, then the payment method bits mentioned above are represented internally as
166 /// [`Method::LdkPaymentHash`]. If the latter, [`Method::UserPaymentHash`].
168 /// For the former method, the payment preimage is constructed as an HMAC of payment metadata and
169 /// random bytes. Because the payment secret is also encoded with these random bytes and metadata
170 /// (with the metadata encrypted with a block cipher), we're able to authenticate the preimage on
173 /// For the latter, the payment secret instead contains an HMAC of the user-provided payment hash
174 /// and payment metadata (encrypted with a block cipher), allowing us to authenticate the payment
175 /// hash and metadata on payment receipt.
177 /// See [`ExpandedKey`] docs for more info on the individual keys used.
179 /// [`KeysInterface::get_inbound_payment_key_material`]: crate::chain::keysinterface::KeysInterface::get_inbound_payment_key_material
180 /// [`create_inbound_payment`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment
181 /// [`create_inbound_payment_for_hash`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment_for_hash
182 pub(super) fn verify<L: Deref>(payment_hash: PaymentHash, payment_data: msgs::FinalOnionHopData, highest_seen_timestamp: u64, keys: &ExpandedKey, logger: &L) -> Result<Option<PaymentPreimage>, ()>
183 where L::Target: Logger
185 let (iv_bytes, metadata_bytes) = decrypt_metadata(payment_data.payment_secret, keys);
187 let payment_type_res = Method::from_bits((metadata_bytes[0] & 0b1110_0000) >> METHOD_TYPE_OFFSET);
188 let mut amt_msat_bytes = [0; AMT_MSAT_LEN];
189 amt_msat_bytes.copy_from_slice(&metadata_bytes[..AMT_MSAT_LEN]);
190 // Zero out the bits reserved to indicate the payment type.
191 amt_msat_bytes[0] &= 0b00011111;
192 let min_amt_msat: u64 = u64::from_be_bytes(amt_msat_bytes.into());
193 let expiry = u64::from_be_bytes(metadata_bytes[AMT_MSAT_LEN..].try_into().unwrap());
195 // Make sure to check to check the HMAC before doing the other checks below, to mitigate timing
197 let mut payment_preimage = None;
198 match payment_type_res {
199 Ok(Method::UserPaymentHash) => {
200 let mut hmac = HmacEngine::<Sha256>::new(&keys.user_pmt_hash_key);
201 hmac.input(&metadata_bytes[..]);
202 hmac.input(&payment_hash.0);
203 if !fixed_time_eq(&iv_bytes, &Hmac::from_engine(hmac).into_inner().split_at_mut(IV_LEN).0) {
204 log_trace!(logger, "Failing HTLC with user-generated payment_hash {}: unexpected payment_secret", log_bytes!(payment_hash.0));
208 Ok(Method::LdkPaymentHash) => {
209 match derive_ldk_payment_preimage(payment_hash, &iv_bytes, &metadata_bytes, keys) {
210 Ok(preimage) => payment_preimage = Some(preimage),
211 Err(bad_preimage_bytes) => {
212 log_trace!(logger, "Failing HTLC with payment_hash {} due to mismatching preimage {}", log_bytes!(payment_hash.0), log_bytes!(bad_preimage_bytes));
217 Err(unknown_bits) => {
218 log_trace!(logger, "Failing HTLC with payment hash {} due to unknown payment type {}", log_bytes!(payment_hash.0), unknown_bits);
223 if payment_data.total_msat < min_amt_msat {
224 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);
228 if expiry < highest_seen_timestamp {
229 log_trace!(logger, "Failing HTLC with payment_hash {}: expired payment", log_bytes!(payment_hash.0));
236 pub(super) fn get_payment_preimage(payment_hash: PaymentHash, payment_secret: PaymentSecret, keys: &ExpandedKey) -> Result<PaymentPreimage, APIError> {
237 let (iv_bytes, metadata_bytes) = decrypt_metadata(payment_secret, keys);
239 match Method::from_bits((metadata_bytes[0] & 0b1110_0000) >> METHOD_TYPE_OFFSET) {
240 Ok(Method::LdkPaymentHash) => {
241 derive_ldk_payment_preimage(payment_hash, &iv_bytes, &metadata_bytes, keys)
242 .map_err(|bad_preimage_bytes| APIError::APIMisuseError {
243 err: format!("Payment hash {} did not match decoded preimage {}", log_bytes!(payment_hash.0), log_bytes!(bad_preimage_bytes))
246 Ok(Method::UserPaymentHash) => Err(APIError::APIMisuseError {
247 err: "Expected payment type to be LdkPaymentHash, instead got UserPaymentHash".to_string()
249 Err(other) => Err(APIError::APIMisuseError { err: format!("Unknown payment type: {}", other) }),
253 fn decrypt_metadata(payment_secret: PaymentSecret, keys: &ExpandedKey) -> ([u8; IV_LEN], [u8; METADATA_LEN]) {
254 let mut iv_bytes = [0; IV_LEN];
255 let (iv_slice, encrypted_metadata_bytes) = payment_secret.0.split_at(IV_LEN);
256 iv_bytes.copy_from_slice(iv_slice);
258 let chacha_block = ChaCha20::get_single_block(&keys.metadata_key, &iv_bytes);
259 let mut metadata_bytes: [u8; METADATA_LEN] = [0; METADATA_LEN];
260 for i in 0..METADATA_LEN {
261 metadata_bytes[i] = chacha_block[i] ^ encrypted_metadata_bytes[i];
264 (iv_bytes, metadata_bytes)
267 // Errors if the payment preimage doesn't match `payment_hash`. Returns the bad preimage bytes in
269 fn derive_ldk_payment_preimage(payment_hash: PaymentHash, iv_bytes: &[u8; IV_LEN], metadata_bytes: &[u8; METADATA_LEN], keys: &ExpandedKey) -> Result<PaymentPreimage, [u8; 32]> {
270 let mut hmac = HmacEngine::<Sha256>::new(&keys.ldk_pmt_hash_key);
271 hmac.input(iv_bytes);
272 hmac.input(metadata_bytes);
273 let decoded_payment_preimage = Hmac::from_engine(hmac).into_inner();
274 if !fixed_time_eq(&payment_hash.0, &Sha256::hash(&decoded_payment_preimage).into_inner()) {
275 return Err(decoded_payment_preimage);
277 return Ok(PaymentPreimage(decoded_payment_preimage))