// This file is Copyright its original authors, visible in version control // history. // // This file is licensed under the Apache License, Version 2.0 or the MIT license // , at your option. // You may not use this file except in accordance with one or both of these // licenses. //! Creating blinded routes and related utilities live here. use bitcoin::hashes::{Hash, HashEngine}; use bitcoin::hashes::sha256::Hash as Sha256; use bitcoin::secp256k1::{self, PublicKey, Scalar, Secp256k1, SecretKey}; use crate::chain::keysinterface::{KeysInterface, Recipient}; use super::packet::ControlTlvs; use super::utils; 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 routes, which serve to hide the identity of /// the recipient. pub struct BlindedRoute { /// To send to a blinded route, 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(super) 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(super) blinding_point: PublicKey, /// The hops composing the blinded route. pub(super) blinded_hops: Vec, } /// Used to construct the blinded hops portion of a blinded route. These hops cannot be identified /// by outside observers and thus can be used to hide the identity of the recipient. pub struct BlindedHop { /// The blinded node id of this hop in a blinded route. pub(super) blinded_node_id: PublicKey, /// The encrypted payload intended for this hop in a blinded route. // The node sending to this blinded route will later encode this payload into the onion packet for // this hop. pub(super) encrypted_payload: Vec, } impl BlindedRoute { /// Create a blinded route 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 (node_pks: &[PublicKey], keys_manager: &K, secp_ctx: &Secp256k1) -> Result { if node_pks.len() < 2 { return Err(()) } let blinding_secret_bytes = keys_manager.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(BlindedRoute { 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 route by one hop, so make the second hop into the new introduction node. pub(super) fn advance_by_one (&mut self, keys_manager: &K, secp_ctx: &Secp256k1) -> Result<(), ()> where K::Target: KeysInterface { let control_tlvs_ss = keys_manager.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( secp_ctx: &Secp256k1, unblinded_path: &[PublicKey], session_priv: &SecretKey ) -> Result, 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(payload: P, encrypted_tlvs_ss: [u8; 32]) -> Vec { 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 BlindedRoute { fn write(&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 BlindedRoute { fn read(r: &mut R) -> Result { 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 = Vec::with_capacity(num_hops.into()); for _ in 0..num_hops { blinded_hops.push(Readable::read(r)?); } Ok(BlindedRoute { 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 route use this value to concatenate the route they find to the /// introduction node with the blinded route. pub(super) next_blinding_override: Option, } /// 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 route that this onion message is /// sending to. This is useful for receivers to check that said blinded route is being used in /// the right context. pub(super) path_id: Option<[u8; 32]>, } impl Writeable for ForwardTlvs { fn write(&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(&self, writer: &mut W) -> Result<(), io::Error> { // TODO: write padding encode_tlv_stream!(writer, { (6, self.path_id, option), }); Ok(()) } }