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[rust-lightning] / 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::{EntropySource, NodeSigner, 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<ES: EntropySource, T: secp256k1::Signing + secp256k1::Verification>
67                 (node_pks: &[PublicKey], entropy_source: &ES, secp_ctx: &Secp256k1<T>) -> Result<Self, ()>
68         {
69                 if node_pks.len() < 2 { return Err(()) }
70                 let blinding_secret_bytes = entropy_source.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<NS: Deref, T: secp256k1::Signing + secp256k1::Verification>
83                 (&mut self, node_signer: &NS, secp_ctx: &Secp256k1<T>) -> Result<(), ()>
84                 where NS::Target: NodeSigner
85         {
86                 let control_tlvs_ss = node_signer.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 }