_ Git - rust-lightning/blob - lightning/src/onion_message/blinded_route.rs

   1 // This file is Copyright its original authors, visible in version control
   2 // history.
   3 //
   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
   8 // licenses.
   9
  10 //! Creating blinded routes and related utilities live here.
  11
  12 use bitcoin::hashes::{Hash, HashEngine};
  13 use bitcoin::hashes::sha256::Hash as Sha256;
  14 use bitcoin::secp256k1::{self, PublicKey, Scalar, Secp256k1, SecretKey};
  15
  16 use crate::chain::keysinterface::{KeysInterface, Recipient};
  17 use super::packet::ControlTlvs;
  18 use super::utils;
  19 use crate::ln::msgs::DecodeError;
  20 use crate::ln::onion_utils;
  21 use crate::util::chacha20poly1305rfc::{ChaChaPolyReadAdapter, ChaChaPolyWriteAdapter};
  22 use crate::util::ser::{FixedLengthReader, LengthReadableArgs, Readable, VecWriter, Writeable, Writer};
  23
  24 use core::mem;
  25 use core::ops::Deref;
  26 use crate::io::{self, Cursor};
  27 use crate::prelude::*;
  28
  29 /// Onion messages can be sent and received to blinded routes, which serve to hide the identity of
  30 /// the recipient.
  31 pub struct BlindedRoute {
  32         /// To send to a blinded route, the sender first finds a route to the unblinded
  33         /// `introduction_node_id`, which can unblind its [`encrypted_payload`] to find out the onion
  34         /// message's next hop and forward it along.
  35         ///
  36         /// [`encrypted_payload`]: BlindedHop::encrypted_payload
  37         pub(super) introduction_node_id: PublicKey,
  38         /// Used by the introduction node to decrypt its [`encrypted_payload`] to forward the onion
  39         /// message.
  40         ///
  41         /// [`encrypted_payload`]: BlindedHop::encrypted_payload
  42         pub(super) blinding_point: PublicKey,
  43         /// The hops composing the blinded route.
  44         pub(super) blinded_hops: Vec<BlindedHop>,
  45 }
  46
  47 /// Used to construct the blinded hops portion of a blinded route. These hops cannot be identified
  48 /// by outside observers and thus can be used to hide the identity of the recipient.
  49 pub struct BlindedHop {
  50         /// The blinded node id of this hop in a blinded route.
  51         pub(super) blinded_node_id: PublicKey,
  52         /// The encrypted payload intended for this hop in a blinded route.
  53         // The node sending to this blinded route will later encode this payload into the onion packet for
  54         // this hop.
  55         pub(super) encrypted_payload: Vec<u8>,
  56 }
  57
  58 impl BlindedRoute {
  59         /// Create a blinded route to be forwarded along `node_pks`. The last node pubkey in `node_pks`
  60         /// will be the destination node.
  61         ///
  62         /// Errors if less than two hops are provided or if `node_pk`(s) are invalid.
  63         //  TODO: make all payloads the same size with padding + add dummy hops
  64         pub fn new<K: KeysInterface, T: secp256k1::Signing + secp256k1::Verification>
  65                 (node_pks: &[PublicKey], keys_manager: &K, secp_ctx: &Secp256k1<T>) -> Result<Self, ()>
  66         {
  67                 if node_pks.len() < 2 { return Err(()) }
  68                 let blinding_secret_bytes = keys_manager.get_secure_random_bytes();
  69                 let blinding_secret = SecretKey::from_slice(&blinding_secret_bytes[..]).expect("RNG is busted");
  70                 let introduction_node_id = node_pks[0];
  71
  72                 Ok(BlindedRoute {
  73                         introduction_node_id,
  74                         blinding_point: PublicKey::from_secret_key(secp_ctx, &blinding_secret),
  75                         blinded_hops: blinded_hops(secp_ctx, node_pks, &blinding_secret).map_err(|_| ())?,
  76                 })
  77         }
  78
  79         // Advance the blinded route by one hop, so make the second hop into the new introduction node.
  80         pub(super) fn advance_by_one<K: Deref, T: secp256k1::Signing + secp256k1::Verification>
  81                 (&mut self, keys_manager: &K, secp_ctx: &Secp256k1<T>) -> Result<(), ()>
  82                 where K::Target: KeysInterface
  83         {
  84                 let control_tlvs_ss = keys_manager.ecdh(Recipient::Node, &self.blinding_point, None)?;
  85                 let rho = onion_utils::gen_rho_from_shared_secret(&control_tlvs_ss.secret_bytes());
  86                 let encrypted_control_tlvs = self.blinded_hops.remove(0).encrypted_payload;
  87                 let mut s = Cursor::new(&encrypted_control_tlvs);
  88                 let mut reader = FixedLengthReader::new(&mut s, encrypted_control_tlvs.len() as u64);
  89                 match ChaChaPolyReadAdapter::read(&mut reader, rho) {
  90                         Ok(ChaChaPolyReadAdapter { readable: ControlTlvs::Forward(ForwardTlvs {
  91                                 mut next_node_id, next_blinding_override,
  92                         })}) => {
  93                                 let mut new_blinding_point = match next_blinding_override {
  94                                         Some(blinding_point) => blinding_point,
  95                                         None => {
  96                                                 let blinding_factor = {
  97                                                         let mut sha = Sha256::engine();
  98                                                         sha.input(&self.blinding_point.serialize()[..]);
  99                                                         sha.input(control_tlvs_ss.as_ref());
 100                                                         Sha256::from_engine(sha).into_inner()
 101                                                 };
 102                                                 self.blinding_point.mul_tweak(secp_ctx, &Scalar::from_be_bytes(blinding_factor).unwrap())
 103                                                         .map_err(|_| ())?
 104                                         }
 105                                 };
 106                                 mem::swap(&mut self.blinding_point, &mut new_blinding_point);
 107                                 mem::swap(&mut self.introduction_node_id, &mut next_node_id);
 108                                 Ok(())
 109                         },
 110                         _ => Err(())
 111                 }
 112         }
 113 }
 114
 115 /// Construct blinded hops for the given `unblinded_path`.
 116 fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
 117         secp_ctx: &Secp256k1<T>, unblinded_path: &[PublicKey], session_priv: &SecretKey
 118 ) -> Result<Vec<BlindedHop>, secp256k1::Error> {
 119         let mut blinded_hops = Vec::with_capacity(unblinded_path.len());
 120
 121         let mut prev_ss_and_blinded_node_id = None;
 122         utils::construct_keys_callback(secp_ctx, unblinded_path, None, session_priv, |blinded_node_id, _, _, encrypted_payload_ss, unblinded_pk, _| {
 123                 if let Some((prev_ss, prev_blinded_node_id)) = prev_ss_and_blinded_node_id {
 124                         if let Some(pk) = unblinded_pk {
 125                                 let payload = ForwardTlvs {
 126                                         next_node_id: pk,
 127                                         next_blinding_override: None,
 128                                 };
 129                                 blinded_hops.push(BlindedHop {
 130                                         blinded_node_id: prev_blinded_node_id,
 131                                         encrypted_payload: encrypt_payload(payload, prev_ss),
 132                                 });
 133                         } else { debug_assert!(false); }
 134                 }
 135                 prev_ss_and_blinded_node_id = Some((encrypted_payload_ss, blinded_node_id));
 136         })?;
 137
 138         if let Some((final_ss, final_blinded_node_id)) = prev_ss_and_blinded_node_id {
 139                 let final_payload = ReceiveTlvs { path_id: None };
 140                 blinded_hops.push(BlindedHop {
 141                         blinded_node_id: final_blinded_node_id,
 142                         encrypted_payload: encrypt_payload(final_payload, final_ss),
 143                 });
 144         } else { debug_assert!(false) }
 145
 146         Ok(blinded_hops)
 147 }
 148
 149 /// Encrypt TLV payload to be used as a [`BlindedHop::encrypted_payload`].
 150 fn encrypt_payload<P: Writeable>(payload: P, encrypted_tlvs_ss: [u8; 32]) -> Vec<u8> {
 151         let mut writer = VecWriter(Vec::new());
 152         let write_adapter = ChaChaPolyWriteAdapter::new(encrypted_tlvs_ss, &payload);
 153         write_adapter.write(&mut writer).expect("In-memory writes cannot fail");
 154         writer.0
 155 }
 156
 157 impl Writeable for BlindedRoute {
 158         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 159                 self.introduction_node_id.write(w)?;
 160                 self.blinding_point.write(w)?;
 161                 (self.blinded_hops.len() as u8).write(w)?;
 162                 for hop in &self.blinded_hops {
 163                         hop.write(w)?;
 164                 }
 165                 Ok(())
 166         }
 167 }
 168
 169 impl Readable for BlindedRoute {
 170         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 171                 let introduction_node_id = Readable::read(r)?;
 172                 let blinding_point = Readable::read(r)?;
 173                 let num_hops: u8 = Readable::read(r)?;
 174                 if num_hops == 0 { return Err(DecodeError::InvalidValue) }
 175                 let mut blinded_hops: Vec<BlindedHop> = Vec::with_capacity(num_hops.into());
 176                 for _ in 0..num_hops {
 177                         blinded_hops.push(Readable::read(r)?);
 178                 }
 179                 Ok(BlindedRoute {
 180                         introduction_node_id,
 181                         blinding_point,
 182                         blinded_hops,
 183                 })
 184         }
 185 }
 186
 187 impl_writeable!(BlindedHop, {
 188         blinded_node_id,
 189         encrypted_payload
 190 });
 191
 192 /// TLVs to encode in an intermediate onion message packet's hop data. When provided in a blinded
 193 /// route, they are encoded into [`BlindedHop::encrypted_payload`].
 194 pub(crate) struct ForwardTlvs {
 195         /// The node id of the next hop in the onion message's path.
 196         pub(super) next_node_id: PublicKey,
 197         /// Senders to a blinded route use this value to concatenate the route they find to the
 198         /// introduction node with the blinded route.
 199         pub(super) next_blinding_override: Option<PublicKey>,
 200 }
 201
 202 /// Similar to [`ForwardTlvs`], but these TLVs are for the final node.
 203 pub(crate) struct ReceiveTlvs {
 204         /// If `path_id` is `Some`, it is used to identify the blinded route that this onion message is
 205         /// sending to. This is useful for receivers to check that said blinded route is being used in
 206         /// the right context.
 207         pub(super) path_id: Option<[u8; 32]>,
 208 }
 209
 210 impl Writeable for ForwardTlvs {
 211         fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
 212                 // TODO: write padding
 213                 encode_tlv_stream!(writer, {
 214                         (4, self.next_node_id, required),
 215                         (8, self.next_blinding_override, option)
 216                 });
 217                 Ok(())
 218         }
 219 }
 220
 221 impl Writeable for ReceiveTlvs {
 222         fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
 223                 // TODO: write padding
 224                 encode_tlv_stream!(writer, {
 225                         (6, self.path_id, option),
 226                 });
 227                 Ok(())
 228         }
 229 }