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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::msgs;
use ln::msgs::MAX_VALUE_MSAT;
use util::chacha20::ChaCha20;
use util::crypto::hkdf_extract_expand_thrice;
use util::errors::APIError;
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;
const METHOD_TYPE_OFFSET: usize = 5;
pub struct ExpandedKey {
metadata_key: [u8; 32],
ldk_pmt_hash_key: [u8; 32],
user_pmt_hash_key: [u8; 32],
}
impl ExpandedKey {
pub 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 fn create<Signer: Sign, K: Deref>(keys: &ExpandedKey, min_value_msat: Option<u64>, invoice_expiry_delta_secs: u32, keys_manager: &K, current_time: 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, current_time)?;
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 fn create_from_hash(keys: &ExpandedKey, min_value_msat: Option<u64>, payment_hash: PaymentHash, invoice_expiry_delta_secs: u32, current_time: u64) -> Result<PaymentSecret, ()> {
let metadata_bytes = construct_metadata_bytes(min_value_msat, Method::UserPaymentHash, invoice_expiry_delta_secs, current_time)?;
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;
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)
}
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]);
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());
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)
}
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))
}