Merge pull request #21 from ideal-lab5/feat/24-derive-msk-in-lib

feat: derive ephem_msk in the lib

core/Cargo.toml

@@ -27,6 +27,7 @@ rand_chacha = { version = "0.3.1" }
 
 [dev-dependencies]
 rand_core = { version = "0.6.4", features = ["getrandom"], default-features = false }
+hkdf = "0.12.4"
 
 [features]
 default = ["client"]

core/src/murmur.rs

@@ -45,7 +45,9 @@ use w3f_bls::{DoublePublicKey, EngineBLS};
 /// Error types for murmur wallet usage
 #[derive(Debug, PartialEq)]
 pub enum Error {
+    /// An error occurred when executing a call
     ExecuteError,
+    /// An error occurred when creating a murmur wallet
     MMRError,
     InconsistentStore,
     /// No leaf could be identified in the MMR at the specified position
@@ -60,6 +62,8 @@ pub enum Error {
     InvalidSeed,
     /// The public key was invalid (could not be decoded)
     InvalidPubkey,
+    /// The key derivation failed
+    KeyDerivationFailed,
 }
 
 /// The murmur store contains minimal data required to use a murmur wallet
@@ -271,10 +275,13 @@ mod tests {
             keypair.public.0,
         );
 
-        let ephem_msk = [1; 32];
         let seed = vec![1, 2, 3];
         let schedule = vec![1, 2, 3];
 
+        let hk = hkdf::Hkdf::<sha3::Sha3_256>::new(None, &seed);
+        let mut ephem_msk = [0u8; 32];
+        hk.expand(b"ephemeral key", &mut ephem_msk).unwrap();
+
         let murmur_store = MurmurStore::new::<TinyBLS377, DummyIdBuilder>(
             seed.clone(),
             schedule.clone(),
@@ -295,14 +302,17 @@ mod tests {
             keypair.public.0,
         );
 
-        let ephem_msk = [1; 32];
         let seed = vec![1, 2, 3];
         let schedule = vec![
             1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
         ];
 
         let aux_data = vec![2, 3, 4, 5];
 
+        let hk = hkdf::Hkdf::<sha3::Sha3_256>::new(None, &seed);
+        let mut ephem_msk = [0u8; 32];
+        hk.expand(b"ephemeral key", &mut ephem_msk).unwrap();
+
         let murmur_store = MurmurStore::new::<TinyBLS377, DummyIdBuilder>(
             seed.clone(),
             schedule.clone(),
@@ -349,12 +359,15 @@ mod tests {
             keypair.public.0,
         );
 
-        let ephem_msk = [1; 32];
         let seed = vec![1, 2, 3];
         let schedule = vec![1, 2, 3, 4, 5];
 
         let aux_data = vec![2, 3, 4, 5];
 
+        let hk = hkdf::Hkdf::<sha3::Sha3_256>::new(None, &seed);
+        let mut ephem_msk = [0u8; 32];
+        hk.expand(b"ephemeral key", &mut ephem_msk).unwrap();
+
         let murmur_store = MurmurStore::new::<TinyBLS377, DummyIdBuilder>(
             seed.clone(),
             schedule.clone(),
@@ -381,12 +394,15 @@ mod tests {
             keypair.public.0,
         );
 
-        let ephem_msk = [1; 32];
         let seed = vec![1, 2, 3];
         let schedule = vec![1, 2, 3];
 
         let aux_data = vec![2, 3, 4, 5];
 
+        let hk = hkdf::Hkdf::<sha3::Sha3_256>::new(None, &seed);
+        let mut ephem_msk = [0u8; 32];
+        hk.expand(b"ephemeral key", &mut ephem_msk).unwrap();
+
         let murmur_store = MurmurStore::new::<TinyBLS377, DummyIdBuilder>(
             seed.clone(),
             schedule.clone(),
@@ -432,13 +448,16 @@ mod tests {
             keypair.public.0,
         );
 
-        let ephem_msk = [1; 32];
         let seed = vec![1, 2, 3];
         let schedule = vec![1, 2, 3];
         let other_schedule = vec![1, 2, 3, 4, 5];
 
         let aux_data = vec![2, 3, 4, 5];
 
+        let hk = hkdf::Hkdf::<sha3::Sha3_256>::new(None, &seed);
+        let mut ephem_msk = [0u8; 32];
+        hk.expand(b"ephemeral key", &mut ephem_msk).unwrap();
+
         let murmur_store = MurmurStore::new::<TinyBLS377, DummyIdBuilder>(
             seed.clone(),
             schedule.clone(),

lib/Cargo.toml

@@ -37,7 +37,8 @@ ark-serialize = "0.4.0"
 w3f-bls = "0.1.3"
 murmur-core = { path = "../core/", features = ["client"] }
 zeroize = "1.8.1"
+hkdf = "0.12.4"
 
 
 [dev-dependencies]
-murmur-test-utils = { path = "../test-utils/" }
+murmur-test-utils = { path = "../test-utils/" }

lib/src/bin/murmur/main.rs

@@ -86,7 +86,6 @@ pub const MMR_STORE_FILEPATH: &str = "mmr_store";
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
     let cli = Cli::parse();
     let before = Instant::now();
-    let ephem_msk = [1; 32];
 
     let (client, current_block_number, round_pubkey_bytes) = idn_connect().await?;
 
@@ -105,7 +104,6 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
             // 2. create mmr
             let create_data = create(
                 args.seed.as_bytes().to_vec(),
-                ephem_msk,
                 schedule,
                 round_pubkey_bytes,
             )

lib/src/lib.rs

@@ -15,6 +15,7 @@
  */
 
 use beefy::{known_payloads, Commitment, Payload};
+use hkdf::Hkdf;
 use murmur_core::types::{Identity, IdentityBuilder};
 use serde::Serialize;
 use subxt::{
@@ -74,16 +75,20 @@ pub struct ProxyData {
 /// Create a new MMR and return the data needed to build a valid call for creating a murmur wallet.
 ///
 /// * `seed`: The seed used to generate otp codes
-/// * `ephem_msk`: An ephemeral secret key TODO: replace with an hkdf?
 /// * `block_schedule`: A list of block numbers when the wallet will be executable
 /// * `round_pubkey_bytes`: The Ideal Network randomness beacon public key
 ///
 pub fn create(
     mut seed: Vec<u8>,
-    mut ephem_msk: [u8; 32],
     block_schedule: Vec<BlockNumber>,
     round_pubkey_bytes: Vec<u8>,
 ) -> Result<CreateData, Error> {
+    // Derive ephem_msk from seed using HKDF
+    let hk = Hkdf::<sha3::Sha3_256>::new(None, &seed);
+    let mut ephem_msk = [0u8; 32];
+    hk.expand(b"ephemeral key", &mut ephem_msk)
+        .map_err(|_| Error::KeyDerivationFailed)?;
+
     let round_pubkey = DoublePublicKey::<TinyBLS377>::from_bytes(&round_pubkey_bytes)
         .map_err(|_| Error::InvalidPubkey)?;
     let mmr_store = MurmurStore::new::<TinyBLS377, BasicIdBuilder>(
@@ -185,17 +190,19 @@ mod tests {
     #[test]
     pub fn it_can_create_an_mmr_store() {
         let seed = b"seed".to_vec();
-        let ephem_msk = [1; 32];
         let block_schedule = vec![1, 2, 3, 4, 5, 6, 7];
         let double_public_bytes = murmur_test_utils::get_dummy_beacon_pubkey();
         let create_data = create(
             seed.clone(),
-            ephem_msk,
             block_schedule.clone(),
             double_public_bytes.clone(),
         )
         .unwrap();
 
+        let hk = Hkdf::<sha3::Sha3_256>::new(None, &seed);
+        let mut ephem_msk = [0u8; 32];
+        hk.expand(b"ephemeral key", &mut ephem_msk).unwrap();
+
         let mmr_store = MurmurStore::new::<TinyBLS377, BasicIdBuilder>(
             seed,
             block_schedule,
@@ -211,11 +218,10 @@ mod tests {
     #[test]
     pub fn it_can_prepare_valid_execution_call_data() {
         let seed = b"seed".to_vec();
-        let ephem_msk = [1; 32];
         let block_schedule = vec![1, 2, 3, 4, 5, 6, 7];
         let double_public_bytes = murmur_test_utils::get_dummy_beacon_pubkey();
         let create_data =
-            create(seed.clone(), ephem_msk, block_schedule, double_public_bytes).unwrap();
+            create(seed.clone(), block_schedule, double_public_bytes).unwrap();
 
         let bob = subxt_signer::sr25519::dev::bob().public_key();
         let balance_transfer_call =