git.bitcoin.ninja Git - rust-lightning/blob - lightning/src/onion_message/blinded_path.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 paths 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 paths, which serve to hide the identity of
  30 /// the recipient.
  31 #[derive(Clone, Debug, PartialEq)]
  32 pub struct BlindedPath {
  33         /// To send to a blinded path, the sender first finds a route to the unblinded
  34         /// `introduction_node_id`, which can unblind its [`encrypted_payload`] to find out the onion
  35         /// message's next hop and forward it along.
  36         ///
  37         /// [`encrypted_payload`]: BlindedHop::encrypted_payload
  38         pub(crate) introduction_node_id: PublicKey,
  39         /// Used by the introduction node to decrypt its [`encrypted_payload`] to forward the onion
  40         /// message.
  41         ///
  42         /// [`encrypted_payload`]: BlindedHop::encrypted_payload
  43         pub(crate) blinding_point: PublicKey,
  44         /// The hops composing the blinded path.
  45         pub(crate) blinded_hops: Vec<BlindedHop>,
  46 }
  47
  48 /// Used to construct the blinded hops portion of a blinded path. These hops cannot be identified
  49 /// by outside observers and thus can be used to hide the identity of the recipient.
  50 #[derive(Clone, Debug, PartialEq)]
  51 pub struct BlindedHop {
  52         /// The blinded node id of this hop in a blinded path.
  53         pub(crate) blinded_node_id: PublicKey,
  54         /// The encrypted payload intended for this hop in a blinded path.
  55         // The node sending to this blinded path will later encode this payload into the onion packet for
  56         // this hop.
  57         pub(crate) encrypted_payload: Vec<u8>,
  58 }
  59
  60 impl BlindedPath {
  61         /// Create a blinded path to be forwarded along `node_pks`. The last node pubkey in `node_pks`
  62         /// will be the destination node.
  63         ///
  64         /// Errors if less than two hops are provided or if `node_pk`(s) are invalid.
  65         //  TODO: make all payloads the same size with padding + add dummy hops
  66         pub fn new<K: KeysInterface, T: secp256k1::Signing + secp256k1::Verification>
  67                 (node_pks: &[PublicKey], keys_manager: &K, secp_ctx: &Secp256k1<T>) -> Result<Self, ()>
  68         {
  69                 if node_pks.len() < 2 { return Err(()) }
  70                 let blinding_secret_bytes = keys_manager.get_secure_random_bytes();
  71                 let blinding_secret = SecretKey::from_slice(&blinding_secret_bytes[..]).expect("RNG is busted");
  72                 let introduction_node_id = node_pks[0];
  73
  74                 Ok(BlindedPath {
  75                         introduction_node_id,
  76                         blinding_point: PublicKey::from_secret_key(secp_ctx, &blinding_secret),
  77                         blinded_hops: blinded_hops(secp_ctx, node_pks, &blinding_secret).map_err(|_| ())?,
  78                 })
  79         }
  80
  81         // Advance the blinded path by one hop, so make the second hop into the new introduction node.
  82         pub(super) fn advance_by_one<K: Deref, T: secp256k1::Signing + secp256k1::Verification>
  83                 (&mut self, keys_manager: &K, secp_ctx: &Secp256k1<T>) -> Result<(), ()>
  84                 where K::Target: KeysInterface
  85         {
  86                 let control_tlvs_ss = keys_manager.ecdh(Recipient::Node, &self.blinding_point, None)?;
  87                 let rho = onion_utils::gen_rho_from_shared_secret(&control_tlvs_ss.secret_bytes());
  88                 let encrypted_control_tlvs = self.blinded_hops.remove(0).encrypted_payload;
  89                 let mut s = Cursor::new(&encrypted_control_tlvs);
  90                 let mut reader = FixedLengthReader::new(&mut s, encrypted_control_tlvs.len() as u64);
  91                 match ChaChaPolyReadAdapter::read(&mut reader, rho) {
  92                         Ok(ChaChaPolyReadAdapter { readable: ControlTlvs::Forward(ForwardTlvs {
  93                                 mut next_node_id, next_blinding_override,
  94                         })}) => {
  95                                 let mut new_blinding_point = match next_blinding_override {
  96                                         Some(blinding_point) => blinding_point,
  97                                         None => {
  98                                                 let blinding_factor = {
  99                                                         let mut sha = Sha256::engine();
 100                                                         sha.input(&self.blinding_point.serialize()[..]);
 101                                                         sha.input(control_tlvs_ss.as_ref());
 102                                                         Sha256::from_engine(sha).into_inner()
 103                                                 };
 104                                                 self.blinding_point.mul_tweak(secp_ctx, &Scalar::from_be_bytes(blinding_factor).unwrap())
 105                                                         .map_err(|_| ())?
 106                                         }
 107                                 };
 108                                 mem::swap(&mut self.blinding_point, &mut new_blinding_point);
 109                                 mem::swap(&mut self.introduction_node_id, &mut next_node_id);
 110                                 Ok(())
 111                         },
 112                         _ => Err(())
 113                 }
 114         }
 115 }
 116
 117 /// Construct blinded hops for the given `unblinded_path`.
 118 fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
 119         secp_ctx: &Secp256k1<T>, unblinded_path: &[PublicKey], session_priv: &SecretKey
 120 ) -> Result<Vec<BlindedHop>, secp256k1::Error> {
 121         let mut blinded_hops = Vec::with_capacity(unblinded_path.len());
 122
 123         let mut prev_ss_and_blinded_node_id = None;
 124         utils::construct_keys_callback(secp_ctx, unblinded_path, None, session_priv, |blinded_node_id, _, _, encrypted_payload_ss, unblinded_pk, _| {
 125                 if let Some((prev_ss, prev_blinded_node_id)) = prev_ss_and_blinded_node_id {
 126                         if let Some(pk) = unblinded_pk {
 127                                 let payload = ForwardTlvs {
 128                                         next_node_id: pk,
 129                                         next_blinding_override: None,
 130                                 };
 131                                 blinded_hops.push(BlindedHop {
 132                                         blinded_node_id: prev_blinded_node_id,
 133                                         encrypted_payload: encrypt_payload(payload, prev_ss),
 134                                 });
 135                         } else { debug_assert!(false); }
 136                 }
 137                 prev_ss_and_blinded_node_id = Some((encrypted_payload_ss, blinded_node_id));
 138         })?;
 139
 140         if let Some((final_ss, final_blinded_node_id)) = prev_ss_and_blinded_node_id {
 141                 let final_payload = ReceiveTlvs { path_id: None };
 142                 blinded_hops.push(BlindedHop {
 143                         blinded_node_id: final_blinded_node_id,
 144                         encrypted_payload: encrypt_payload(final_payload, final_ss),
 145                 });
 146         } else { debug_assert!(false) }
 147
 148         Ok(blinded_hops)
 149 }
 150
 151 /// Encrypt TLV payload to be used as a [`BlindedHop::encrypted_payload`].
 152 fn encrypt_payload<P: Writeable>(payload: P, encrypted_tlvs_ss: [u8; 32]) -> Vec<u8> {
 153         let mut writer = VecWriter(Vec::new());
 154         let write_adapter = ChaChaPolyWriteAdapter::new(encrypted_tlvs_ss, &payload);
 155         write_adapter.write(&mut writer).expect("In-memory writes cannot fail");
 156         writer.0
 157 }
 158
 159 impl Writeable for BlindedPath {
 160         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 161                 self.introduction_node_id.write(w)?;
 162                 self.blinding_point.write(w)?;
 163                 (self.blinded_hops.len() as u8).write(w)?;
 164                 for hop in &self.blinded_hops {
 165                         hop.write(w)?;
 166                 }
 167                 Ok(())
 168         }
 169 }
 170
 171 impl Readable for BlindedPath {
 172         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 173                 let introduction_node_id = Readable::read(r)?;
 174                 let blinding_point = Readable::read(r)?;
 175                 let num_hops: u8 = Readable::read(r)?;
 176                 if num_hops == 0 { return Err(DecodeError::InvalidValue) }
 177                 let mut blinded_hops: Vec<BlindedHop> = Vec::with_capacity(num_hops.into());
 178                 for _ in 0..num_hops {
 179                         blinded_hops.push(Readable::read(r)?);
 180                 }
 181                 Ok(BlindedPath {
 182                         introduction_node_id,
 183                         blinding_point,
 184                         blinded_hops,
 185                 })
 186         }
 187 }
 188
 189 impl_writeable!(BlindedHop, {
 190         blinded_node_id,
 191         encrypted_payload
 192 });
 193
 194 /// TLVs to encode in an intermediate onion message packet's hop data. When provided in a blinded
 195 /// route, they are encoded into [`BlindedHop::encrypted_payload`].
 196 pub(crate) struct ForwardTlvs {
 197         /// The node id of the next hop in the onion message's path.
 198         pub(super) next_node_id: PublicKey,
 199         /// Senders to a blinded path use this value to concatenate the route they find to the
 200         /// introduction node with the blinded path.
 201         pub(super) next_blinding_override: Option<PublicKey>,
 202 }
 203
 204 /// Similar to [`ForwardTlvs`], but these TLVs are for the final node.
 205 pub(crate) struct ReceiveTlvs {
 206         /// If `path_id` is `Some`, it is used to identify the blinded path that this onion message is
 207         /// sending to. This is useful for receivers to check that said blinded path is being used in
 208         /// the right context.
 209         pub(super) path_id: Option<[u8; 32]>,
 210 }
 211
 212 impl Writeable for ForwardTlvs {
 213         fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
 214                 // TODO: write padding
 215                 encode_tlv_stream!(writer, {
 216                         (4, self.next_node_id, required),
 217                         (8, self.next_blinding_override, option)
 218                 });
 219                 Ok(())
 220         }
 221 }
 222
 223 impl Writeable for ReceiveTlvs {
 224         fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
 225                 // TODO: write padding
 226                 encode_tlv_stream!(writer, {
 227                         (6, self.path_id, option),
 228                 });
 229                 Ok(())
 230         }
 231 }