Add support for secp256k1 consensus keys (informalsystems#1358)

* support secp256k1 curve in priv_validator_key.json

* fix invalid comments

* fix inconsistent variable naming

* fix clippy lints

* Add changelog entry

---------

Co-authored-by: Romain Ruetschi <[email protected]>

.changelog/unreleased/features/1364-secp256k1-keys.md

@@ -0,0 +1,2 @@
+- `[tendermint]` Add support for secp256k1 consensus keys
+  ([\#1364](https://github.com/informalsystems/tendermint-rs/issues/1364))

config/Cargo.toml

@@ -33,3 +33,6 @@ url = { version = "2.2" }
 
 [dev-dependencies]
 pretty_assertions = "1.3.0"
+
+[features]
+secp256k1 = ["tendermint/secp256k1"]

config/tests/mod.rs

@@ -213,17 +213,29 @@ fn node_key_parser() {
     );
 }
 
-/// Parse an example `priv_validator_key.json` to a `PrivValidatorKey` struct
+/// Parse an example `priv_validator_key.ed25519.json` to a `PrivValidatorKey` struct
 #[test]
-fn priv_validator_json_parser() {
-    let raw_priv_validator_key = read_fixture("priv_validator_key.json");
+fn priv_validator_ed25519_json_parser() {
+    let raw_priv_validator_key = read_fixture("priv_validator_key.ed25519.json");
     let priv_validator_key = PrivValidatorKey::parse_json(raw_priv_validator_key).unwrap();
     assert_eq!(
         priv_validator_key.consensus_pubkey().public_key().to_hex(),
         "F26BF4B2A2E84CEB7A53C3F1AE77408779B20064782FBADBDF0E365959EE4534"
     );
 }
 
+/// Parse an example `priv_validator_key.secp256k1.json` to a `PrivValidatorKey` struct
+#[test]
+#[cfg(feature = "secp256k1")]
+fn priv_validator_secp256k1_json_parser() {
+    let raw_priv_validator_key = read_fixture("priv_validator_key.secp256k1.json");
+    let priv_validator_key = PrivValidatorKey::parse_json(raw_priv_validator_key).unwrap();
+    assert_eq!(
+        priv_validator_key.consensus_pubkey().public_key().to_hex(),
+        "03685D6F62E54D0FACC6AA649E4036BF446043A6BA438B793B085E6C8A92AFCAAE"
+    );
+}
+
 /// Parse an example `config.toml` file to a `TendermintConfig` struct, then
 /// serialize it and parse again.
 #[test]

config/tests/support/config/priv_validator_key.secp256k1.json

@@ -0,0 +1,11 @@
+{
+  "address": "0799B6E1F13F1ECC7E891765F499A73665F42866",
+  "pub_key": {
+    "type": "tendermint/PubKeySecp256k1",
+    "value": "A2hdb2LlTQ+sxqpknkA2v0RgQ6a6Q4t5OwhebIqSr8qu"
+  },
+  "priv_key": {
+    "type": "tendermint/PrivKeySecp256k1",
+    "value": "aVmw0npSBEqPU4v6qEZ9o3z5nCpHjicwFDdIBRUbSrM="
+  }
+}

tendermint/src/private_key.rs

@@ -1,6 +1,9 @@
 //! Cryptographic private keys
 
 pub use crate::crypto::ed25519::SigningKey as Ed25519;
+#[cfg(feature = "secp256k1")]
+pub use k256::ecdsa::SigningKey as Secp256k1;
+
 use crate::prelude::*;
 
 #[cfg(feature = "rust-crypto")]
@@ -14,6 +17,7 @@ use subtle_encoding::{Base64, Encoding};
 use zeroize::Zeroizing;
 
 pub const ED25519_KEYPAIR_SIZE: usize = 64;
+pub const SECP256K1_KEY_SIZE: usize = 32;
 
 /// Private keys as parsed from configuration files
 #[cfg_attr(feature = "rust-crypto", derive(Serialize, Deserialize))]
@@ -30,6 +34,15 @@ pub enum PrivateKey {
         )
     )]
     Ed25519(Ed25519),
+
+    #[cfg(feature = "secp256k1")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "secp256k1")))]
+    #[serde(
+        rename = "tendermint/PrivKeySecp256k1",
+        serialize_with = "serialize_secp256k1_privkey",
+        deserialize_with = "deserialize_secp256k1_privkey"
+    )]
+    Secp256k1(Secp256k1),
 }
 
 impl PrivateKey {
@@ -38,17 +51,58 @@ impl PrivateKey {
     pub fn public_key(&self) -> PublicKey {
         match self {
             PrivateKey::Ed25519(signing_key) => PublicKey::Ed25519(signing_key.verification_key()),
+
+            #[cfg(feature = "secp256k1")]
+            PrivateKey::Secp256k1(signing_key) => {
+                PublicKey::Secp256k1(*signing_key.verifying_key())
+            },
         }
     }
 
     /// If applicable, borrow the Ed25519 keypair
     pub fn ed25519_signing_key(&self) -> Option<&Ed25519> {
         match self {
             PrivateKey::Ed25519(signing_key) => Some(signing_key),
+
+            #[cfg(feature = "secp256k1")]
+            PrivateKey::Secp256k1(_signing_key) => None,
         }
     }
 }
 
+/// Serialize a Secp256k1 privkey as Base64
+#[cfg(feature = "secp256k1")]
+fn serialize_secp256k1_privkey<S>(signing_key: &Secp256k1, serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: ser::Serializer,
+{
+    Zeroizing::new(String::from_utf8(Base64::default().encode(signing_key.to_bytes())).unwrap())
+        .serialize(serializer)
+}
+
+/// Deserialize a Secp256k1 privkey from Base64
+#[cfg(feature = "secp256k1")]
+fn deserialize_secp256k1_privkey<'de, D>(deserializer: D) -> Result<Secp256k1, D::Error>
+where
+    D: de::Deserializer<'de>,
+{
+    use de::Error;
+    let string = Zeroizing::new(String::deserialize(deserializer)?);
+    let mut privkey_bytes = Zeroizing::new([0u8; SECP256K1_KEY_SIZE]);
+    let decoded_len = Base64::default()
+        .decode_to_slice(string.as_bytes(), &mut *privkey_bytes)
+        .map_err(D::Error::custom)?;
+
+    if decoded_len != SECP256K1_KEY_SIZE {
+        return Err(D::Error::custom("invalid sepc256k1 privkey size"));
+    }
+
+    let signing_key = Secp256k1::try_from(&privkey_bytes[0..SECP256K1_KEY_SIZE])
+        .map_err(|_| D::Error::custom("invalid signing key"))?;
+
+    Ok(signing_key)
+}
+
 /// Serialize an Ed25519 keypair as Base64
 #[cfg(feature = "rust-crypto")]
 fn serialize_ed25519_keypair<S>(signing_key: &Ed25519, serializer: S) -> Result<S::Ok, S::Error>

tendermint/src/public_key.rs

@@ -290,8 +290,11 @@ impl TendermintKey {
         #[allow(unreachable_patterns)]
         match public_key {
             PublicKey::Ed25519(_) => Ok(TendermintKey::AccountKey(public_key)),
+            #[cfg(feature = "secp256k1")]
+            PublicKey::Secp256k1(_) => Ok(TendermintKey::AccountKey(public_key)),
+
             _ => Err(Error::invalid_key(
-                "only ed25519 consensus keys are supported".to_string(),
+                "only ed25519 or secp256k1 consensus keys are supported".to_string(),
             )),
         }
     }