+// This file is Copyright its original authors, visible in version control
+// history.
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! Creating blinded paths and related utilities live here.
+
+pub(crate) mod utils;
+
+use bitcoin::hashes::{Hash, HashEngine};
+use bitcoin::hashes::sha256::Hash as Sha256;
+use bitcoin::secp256k1::{self, PublicKey, Scalar, Secp256k1, SecretKey};
+
+use crate::chain::keysinterface::{EntropySource, NodeSigner, Recipient};
+use crate::onion_message::ControlTlvs;
+use crate::ln::msgs::DecodeError;
+use crate::ln::onion_utils;
+use crate::util::chacha20poly1305rfc::{ChaChaPolyReadAdapter, ChaChaPolyWriteAdapter};
+use crate::util::ser::{FixedLengthReader, LengthReadableArgs, Readable, VecWriter, Writeable, Writer};
+
+use core::mem;
+use core::ops::Deref;
+use crate::io::{self, Cursor};
+use crate::prelude::*;
+
+/// Onion messages can be sent and received to blinded paths, which serve to hide the identity of
+/// the recipient.
+#[derive(Clone, Debug, PartialEq)]
+pub struct BlindedPath {
+ /// To send to a blinded path, the sender first finds a route to the unblinded
+ /// `introduction_node_id`, which can unblind its [`encrypted_payload`] to find out the onion
+ /// message's next hop and forward it along.
+ ///
+ /// [`encrypted_payload`]: BlindedHop::encrypted_payload
+ pub(crate) introduction_node_id: PublicKey,
+ /// Used by the introduction node to decrypt its [`encrypted_payload`] to forward the onion
+ /// message.
+ ///
+ /// [`encrypted_payload`]: BlindedHop::encrypted_payload
+ pub(crate) blinding_point: PublicKey,
+ /// The hops composing the blinded path.
+ pub(crate) blinded_hops: Vec<BlindedHop>,
+}
+
+/// Used to construct the blinded hops portion of a blinded path. These hops cannot be identified
+/// by outside observers and thus can be used to hide the identity of the recipient.
+#[derive(Clone, Debug, PartialEq)]
+pub struct BlindedHop {
+ /// The blinded node id of this hop in a blinded path.
+ pub(crate) blinded_node_id: PublicKey,
+ /// The encrypted payload intended for this hop in a blinded path.
+ // The node sending to this blinded path will later encode this payload into the onion packet for
+ // this hop.
+ pub(crate) encrypted_payload: Vec<u8>,
+}
+
+impl BlindedPath {
+ /// Create a blinded path to be forwarded along `node_pks`. The last node pubkey in `node_pks`
+ /// will be the destination node.
+ ///
+ /// Errors if less than two hops are provided or if `node_pk`(s) are invalid.
+ // TODO: make all payloads the same size with padding + add dummy hops
+ pub fn new<ES: EntropySource, T: secp256k1::Signing + secp256k1::Verification>
+ (node_pks: &[PublicKey], entropy_source: &ES, secp_ctx: &Secp256k1<T>) -> Result<Self, ()>
+ {
+ if node_pks.len() < 2 { return Err(()) }
+ let blinding_secret_bytes = entropy_source.get_secure_random_bytes();
+ let blinding_secret = SecretKey::from_slice(&blinding_secret_bytes[..]).expect("RNG is busted");
+ let introduction_node_id = node_pks[0];
+
+ Ok(BlindedPath {
+ introduction_node_id,
+ blinding_point: PublicKey::from_secret_key(secp_ctx, &blinding_secret),
+ blinded_hops: blinded_hops(secp_ctx, node_pks, &blinding_secret).map_err(|_| ())?,
+ })
+ }
+
+ // Advance the blinded path by one hop, so make the second hop into the new introduction node.
+ pub(super) fn advance_by_one<NS: Deref, T: secp256k1::Signing + secp256k1::Verification>
+ (&mut self, node_signer: &NS, secp_ctx: &Secp256k1<T>) -> Result<(), ()>
+ where NS::Target: NodeSigner
+ {
+ let control_tlvs_ss = node_signer.ecdh(Recipient::Node, &self.blinding_point, None)?;
+ let rho = onion_utils::gen_rho_from_shared_secret(&control_tlvs_ss.secret_bytes());
+ let encrypted_control_tlvs = self.blinded_hops.remove(0).encrypted_payload;
+ let mut s = Cursor::new(&encrypted_control_tlvs);
+ let mut reader = FixedLengthReader::new(&mut s, encrypted_control_tlvs.len() as u64);
+ match ChaChaPolyReadAdapter::read(&mut reader, rho) {
+ Ok(ChaChaPolyReadAdapter { readable: ControlTlvs::Forward(ForwardTlvs {
+ mut next_node_id, next_blinding_override,
+ })}) => {
+ let mut new_blinding_point = match next_blinding_override {
+ Some(blinding_point) => blinding_point,
+ None => {
+ let blinding_factor = {
+ let mut sha = Sha256::engine();
+ sha.input(&self.blinding_point.serialize()[..]);
+ sha.input(control_tlvs_ss.as_ref());
+ Sha256::from_engine(sha).into_inner()
+ };
+ self.blinding_point.mul_tweak(secp_ctx, &Scalar::from_be_bytes(blinding_factor).unwrap())
+ .map_err(|_| ())?
+ }
+ };
+ mem::swap(&mut self.blinding_point, &mut new_blinding_point);
+ mem::swap(&mut self.introduction_node_id, &mut next_node_id);
+ Ok(())
+ },
+ _ => Err(())
+ }
+ }
+}
+
+/// Construct blinded hops for the given `unblinded_path`.
+fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
+ secp_ctx: &Secp256k1<T>, unblinded_path: &[PublicKey], session_priv: &SecretKey
+) -> Result<Vec<BlindedHop>, secp256k1::Error> {
+ let mut blinded_hops = Vec::with_capacity(unblinded_path.len());
+
+ let mut prev_ss_and_blinded_node_id = None;
+ utils::construct_keys_callback(secp_ctx, unblinded_path, None, session_priv, |blinded_node_id, _, _, encrypted_payload_ss, unblinded_pk, _| {
+ if let Some((prev_ss, prev_blinded_node_id)) = prev_ss_and_blinded_node_id {
+ if let Some(pk) = unblinded_pk {
+ let payload = ForwardTlvs {
+ next_node_id: pk,
+ next_blinding_override: None,
+ };
+ blinded_hops.push(BlindedHop {
+ blinded_node_id: prev_blinded_node_id,
+ encrypted_payload: encrypt_payload(payload, prev_ss),
+ });
+ } else { debug_assert!(false); }
+ }
+ prev_ss_and_blinded_node_id = Some((encrypted_payload_ss, blinded_node_id));
+ })?;
+
+ if let Some((final_ss, final_blinded_node_id)) = prev_ss_and_blinded_node_id {
+ let final_payload = ReceiveTlvs { path_id: None };
+ blinded_hops.push(BlindedHop {
+ blinded_node_id: final_blinded_node_id,
+ encrypted_payload: encrypt_payload(final_payload, final_ss),
+ });
+ } else { debug_assert!(false) }
+
+ Ok(blinded_hops)
+}
+
+/// Encrypt TLV payload to be used as a [`BlindedHop::encrypted_payload`].
+fn encrypt_payload<P: Writeable>(payload: P, encrypted_tlvs_ss: [u8; 32]) -> Vec<u8> {
+ let mut writer = VecWriter(Vec::new());
+ let write_adapter = ChaChaPolyWriteAdapter::new(encrypted_tlvs_ss, &payload);
+ write_adapter.write(&mut writer).expect("In-memory writes cannot fail");
+ writer.0
+}
+
+impl Writeable for BlindedPath {
+ fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+ self.introduction_node_id.write(w)?;
+ self.blinding_point.write(w)?;
+ (self.blinded_hops.len() as u8).write(w)?;
+ for hop in &self.blinded_hops {
+ hop.write(w)?;
+ }
+ Ok(())
+ }
+}
+
+impl Readable for BlindedPath {
+ fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
+ let introduction_node_id = Readable::read(r)?;
+ let blinding_point = Readable::read(r)?;
+ let num_hops: u8 = Readable::read(r)?;
+ if num_hops == 0 { return Err(DecodeError::InvalidValue) }
+ let mut blinded_hops: Vec<BlindedHop> = Vec::with_capacity(num_hops.into());
+ for _ in 0..num_hops {
+ blinded_hops.push(Readable::read(r)?);
+ }
+ Ok(BlindedPath {
+ introduction_node_id,
+ blinding_point,
+ blinded_hops,
+ })
+ }
+}
+
+impl_writeable!(BlindedHop, {
+ blinded_node_id,
+ encrypted_payload
+});
+
+/// TLVs to encode in an intermediate onion message packet's hop data. When provided in a blinded
+/// route, they are encoded into [`BlindedHop::encrypted_payload`].
+pub(crate) struct ForwardTlvs {
+ /// The node id of the next hop in the onion message's path.
+ pub(super) next_node_id: PublicKey,
+ /// Senders to a blinded path use this value to concatenate the route they find to the
+ /// introduction node with the blinded path.
+ pub(super) next_blinding_override: Option<PublicKey>,
+}
+
+/// Similar to [`ForwardTlvs`], but these TLVs are for the final node.
+pub(crate) struct ReceiveTlvs {
+ /// If `path_id` is `Some`, it is used to identify the blinded path that this onion message is
+ /// sending to. This is useful for receivers to check that said blinded path is being used in
+ /// the right context.
+ pub(super) path_id: Option<[u8; 32]>,
+}
+
+impl Writeable for ForwardTlvs {
+ fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
+ // TODO: write padding
+ encode_tlv_stream!(writer, {
+ (4, self.next_node_id, required),
+ (8, self.next_blinding_override, option)
+ });
+ Ok(())
+ }
+}
+
+impl Writeable for ReceiveTlvs {
+ fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
+ // TODO: write padding
+ encode_tlv_stream!(writer, {
+ (6, self.path_id, option),
+ });
+ Ok(())
+ }
+}