node: implement node announcement sybil resistance

We implement a small proof-of-work on the node announcement message to prevent the routing table from being filled by fake entries. Signed-off-by: Alexis Sellier <alexis@radicle.xyz>
2022-10-30 10:21:32 +01:00 · 2022-10-30 10:21:32 +01:00 · 7b7e83fbc7
parent 3c900f106f
commit 7b7e83fbc7
6 changed files with 172 additions and 12 deletions
--- a/Cargo.lock
+++ b/Cargo.lock
@ -255,6 +255,16 @@ dependencies = [
 "winapi",
 ]

+[[package]]
+name = "cipher"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d1873270f8f7942c191139cb8a40fd228da6c3fd2fc376d7e92d47aa14aeb59e"
+dependencies = [
+ "crypto-common",
+ "inout",
+]
+
 [[package]]
 name = "colored"
 version = "1.9.3"
@ -374,6 +384,7 @@ checksum = "adfbc57365a37acbd2ebf2b64d7e69bb766e2fea813521ed536f5d0520dcf86c"
 dependencies = [
 "block-buffer 0.10.3",
 "crypto-common",
+ "subtle",
 ]

 [[package]]
@ -572,6 +583,15 @@ dependencies = [
 "libc",
 ]

+[[package]]
+name = "hmac"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c49c37c09c17a53d937dfbb742eb3a961d65a994e6bcdcf37e7399d0cc8ab5e"
+dependencies = [
+ "digest 0.10.5",
+]
+
 [[package]]
 name = "home"
 version = "0.5.3"
@ -678,6 +698,15 @@ dependencies = [
 "hashbrown",
 ]

+[[package]]
+name = "inout"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a0c10553d664a4d0bcff9f4215d0aac67a639cc68ef660840afe309b807bc9f5"
+dependencies = [
+ "generic-array",
+]
+
 [[package]]
 name = "instant"
 version = "0.1.12"
@ -952,6 +981,15 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b15813163c1d831bf4a13c3610c05c0d03b39feb07f7e09fa234dac9b15aaf39"

+[[package]]
+name = "pbkdf2"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "83a0692ec44e4cf1ef28ca317f14f8f07da2d95ec3fa01f86e4467b725e60917"
+dependencies = [
+ "digest 0.10.5",
+]
+
 [[package]]
 name = "percent-encoding"
 version = "2.2.0"
@ -1178,6 +1216,7 @@ dependencies = [
 "quickcheck",
 "quickcheck_macros",
 "radicle",
+ "scrypt",
 "serde",
 "serde_json",
 "sqlite",
@ -1286,6 +1325,27 @@ version = "1.0.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4501abdff3ae82a1c1b477a17252eb69cee9e66eb915c1abaa4f44d873df9f09"

+[[package]]
+name = "salsa20"
+version = "0.10.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "97a22f5af31f73a954c10289c93e8a50cc23d971e80ee446f1f6f7137a088213"
+dependencies = [
+ "cipher",
+]
+
+[[package]]
+name = "scrypt"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9f9e24d2b632954ded8ab2ef9fea0a0c769ea56ea98bddbafbad22caeeadf45d"
+dependencies = [
+ "hmac",
+ "pbkdf2",
+ "salsa20",
+ "sha2 0.10.6",
+]
+
 [[package]]
 name = "serde"
 version = "1.0.145"
@ -1437,6 +1497,12 @@ dependencies = [
 "sqlite3-src",
 ]

+[[package]]
+name = "subtle"
+version = "2.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6bdef32e8150c2a081110b42772ffe7d7c9032b606bc226c8260fd97e0976601"
+
 [[package]]
 name = "syn"
 version = "1.0.101"
--- a/radicle-node/Cargo.toml
+++ b/radicle-node/Cargo.toml
@ -21,6 +21,7 @@ nakamoto-net-poll = { version = "0.3.0" }
 nonempty = { version = "0.8.0", features = ["serialize"] }
 sqlite = { version = "0.27.0" }
 sqlite3-src = { version = "0.4.0", features = ["bundled"] } # Ensures static linking
+scrypt = { version = "0.10.0", default-features = false }
 serde = { version = "1", features = ["derive"] }
 serde_json = { version = "1", features = ["preserve_order"] }
 tempfile = { version = "3.3.0" }
--- a/radicle-node/src/service.rs
+++ b/radicle-node/src/service.rs
@ -687,23 +687,24 @@ where
                    }
                }
            }
-            AnnouncementMessage::Node(NodeAnnouncement {
+            AnnouncementMessage::Node(
+                ann @ NodeAnnouncement {
                    features,
                    alias,
                    addresses,
                    ..
-            }) => {
+                },
+            ) => {
                // Discard node messages we've already seen, otherwise update
-                // out last seen time.
+                // our last seen time.
                if !peer.node_announced(timestamp) {
                    debug!("Ignoring stale node announcement from {announcer}");
                    return Ok(false);
                }

-                // If this node isn't a seed, we're not interested in adding it
-                // to our address book, but other nodes may be, so we relay the message anyway.
-                if !features.has(Features::SEED) {
-                    return Ok(relay);
+                if !ann.validate() {
+                    warn!("Dropping node announcement from {announcer}: invalid proof-of-work");
+                    return Ok(false);
                }

                let alias = match str::from_utf8(alias) {
@ -714,6 +715,12 @@ where
                    }
                };

+                // If this node isn't a seed, we're not interested in adding it
+                // to our address book, but other nodes may be, so we relay the message anyway.
+                if !features.has(Features::SEED) {
+                    return Ok(relay);
+                }
+
                match self.addresses.insert(
                    announcer,
                    *features,
@ -1223,7 +1230,9 @@ mod gossip {
            timestamp,
            alias,
            addresses,
+            nonce: 0,
        }
+        .solve()
    }

    pub fn inventory(timestamp: Timestamp, inventory: Vec<Id>) -> InventoryAnnouncement {
--- a/radicle-node/src/service/message.rs
+++ b/radicle-node/src/service/message.rs
@ -133,6 +133,52 @@ pub struct NodeAnnouncement {
    pub alias: [u8; 32],
    /// Announced addresses.
    pub addresses: Vec<Address>,
+    /// Nonce used for announcement proof-of-work.
+    pub nonce: u64,
+}
+
+impl NodeAnnouncement {
+    /// Validate a node announcement message.
+    ///
+    /// Checks that the proof-of-work is valid, by generating a single byte that
+    /// must be zero.
+    ///
+    /// `scrypt(encode(announcement)) == 0`
+    ///
+    pub fn validate(&self) -> bool {
+        let (n, r, p) = Announcement::POW_PARAMS;
+        let params = scrypt::Params::new(n, r, p).expect("proof-of-work parameters are valid");
+        let mut output = [0; 1];
+
+        scrypt::scrypt(
+            wire::serialize(self).as_ref(),
+            Announcement::POW_SALT,
+            &params,
+            &mut output,
+        )
+        .expect("proof-of-work output vector is a valid length");
+
+        output == [0]
+    }
+
+    /// Solve the proof-of-work of a node announcement by iterating through different nonces.
+    pub fn solve(mut self) -> Self {
+        loop {
+            if let Some(nonce) = self.nonce.checked_add(1) {
+                self.nonce = nonce;
+
+                if self.validate() {
+                    break;
+                }
+            } else {
+                // If a very high difficulty is chosen, it's possible to iterate through all
+                // possible values of the nonce without solving the puzzle. However, with "normal"
+                // values, this is virtually impossible.
+                panic!("could not solve proof-of-work!");
+            }
+        }
+        self
+    }
 }

 impl wire::Encode for NodeAnnouncement {
@ -143,6 +189,7 @@ impl wire::Encode for NodeAnnouncement {
        n += self.timestamp.encode(writer)?;
        n += self.alias.encode(writer)?;
        n += self.addresses.as_slice().encode(writer)?;
+        n += self.nonce.encode(writer)?;

        Ok(n)
    }
@ -154,12 +201,14 @@ impl wire::Decode for NodeAnnouncement {
        let timestamp = Timestamp::decode(reader)?;
        let alias = wire::Decode::decode(reader)?;
        let addresses = Vec::<Address>::decode(reader)?;
+        let nonce = u64::decode(reader)?;

        Ok(Self {
            features,
            timestamp,
            alias,
            addresses,
+            nonce,
        })
    }
 }
@ -271,6 +320,24 @@ pub struct Announcement {
 }

 impl Announcement {
+    /// Proof-of-work parameters for announcements.
+    ///
+    /// These parameters are fed into `scrypt`.
+    /// They represent the `log2(N)`, `r`, `p` parameters, respectively.
+    ///
+    /// * log2(N) – iterations count (affects memory and CPU usage), e.g. 15
+    /// * r – block size (affects memory and CPU usage), e.g. 8
+    /// * p – parallelism factor (threads to run in parallel - affects the memory, CPU usage), usually 1
+    ///
+    /// `15, 8, 1` are usually the recommended parameters.
+    ///
+    #[cfg(test)]
+    pub const POW_PARAMS: (u8, u32, u32) = (1, 1, 1);
+    #[cfg(not(test))]
+    pub const POW_PARAMS: (u8, u32, u32) = (15, 8, 1);
+    /// Salt used for generating PoW.
+    pub const POW_SALT: &[u8] = &[b'r', b'a', b'd'];
+
    /// Verify this announcement's signature.
    pub fn verify(&self) -> bool {
        let msg = wire::serialize(&self.message);
@ -447,4 +514,18 @@ mod tests {

        assert!(ann.verify());
    }
+
+    #[test]
+    fn test_node_announcement_validate() {
+        let ann = NodeAnnouncement {
+            features: node::Features::SEED,
+            timestamp: 42491841,
+            alias: [0; 32],
+            addresses: vec![],
+            nonce: 0,
+        };
+
+        assert!(!ann.validate());
+        assert!(ann.solve().validate());
+    }
 }
--- a/radicle-node/src/test/arbitrary.rs
+++ b/radicle-node/src/test/arbitrary.rs
@ -69,6 +69,7 @@ impl Arbitrary for Message {
                    timestamp: Timestamp::arbitrary(g),
                    alias: ByteArray::<32>::arbitrary(g).into_inner(),
                    addresses: Arbitrary::arbitrary(g),
+                    nonce: u64::arbitrary(g),
                }
                .into();
                let bytes: ByteArray<64> = Arbitrary::arbitrary(g);
--- a/radicle-node/src/test/peer.rs
+++ b/radicle-node/src/test/peer.rs
@ -164,7 +164,9 @@ where
                timestamp: self.timestamp(),
                alias,
                addresses: vec![net::SocketAddr::from((self.ip, service::DEFAULT_PORT)).into()],
-            },
+                nonce: 0,
+            }
+            .solve(),
            self.signer(),
        )
    }