check if the correct number of identifiers was provided in split() (#481)

frost-core/src/frost/keys.rs

@@ -473,18 +473,25 @@ pub fn split<C: Ciphersuite, R: RngCore + CryptoRng>(
 ) -> Result<(HashMap<Identifier<C>, SecretShare<C>>, PublicKeyPackage<C>), Error<C>> {
     validate_num_of_signers(min_signers, max_signers)?;
 
+    if let IdentifierList::Custom(identifiers) = &identifiers {
+        if identifiers.len() != max_signers as usize {
+            return Err(Error::IncorrectNumberOfIdentifiers);
+        }
+    }
+
     let group_public = VerifyingKey::from(key);
 
     let coefficients = generate_coefficients::<C, R>(min_signers as usize - 1, rng);
 
-    let default_identifiers = default_identifiers(max_signers);
-    let identifiers = match identifiers {
-        IdentifierList::Custom(identifiers) => identifiers,
-        IdentifierList::Default => &default_identifiers,
+    let secret_shares = match identifiers {
+        IdentifierList::Default => {
+            let identifiers = default_identifiers(max_signers);
+            generate_secret_shares(key, max_signers, min_signers, coefficients, &identifiers)?
+        }
+        IdentifierList::Custom(identifiers) => {
+            generate_secret_shares(key, max_signers, min_signers, coefficients, identifiers)?
+        }
     };
-
-    let secret_shares =
-        generate_secret_shares(key, max_signers, min_signers, coefficients, identifiers)?;
     let mut signer_pubkeys: HashMap<Identifier<C>, VerifyingShare<C>> =
         HashMap::with_capacity(max_signers as usize);
 

frost-core/src/tests/ciphersuite_generic.rs

@@ -506,13 +506,13 @@ fn check_part3_different_participants<C: Ciphersuite>(
 pub fn check_sign_with_dealer_and_identifiers<C: Ciphersuite, R: RngCore + CryptoRng>(
     mut rng: R,
 ) -> (Vec<u8>, Signature<C>, VerifyingKey<C>) {
-    // Check error case first (repeated identifiers)
+    // Check error cases first
+    // Check repeated identifiers
 
     let identifiers: Vec<frost::Identifier<C>> = [1u16, 42, 100, 257, 42]
         .into_iter()
         .map(|i| i.try_into().unwrap())
         .collect();
-
     let max_signers = 5;
     let min_signers = 3;
     let err = frost::keys::generate_with_dealer(
@@ -524,6 +524,23 @@ pub fn check_sign_with_dealer_and_identifiers<C: Ciphersuite, R: RngCore + Crypt
     .unwrap_err();
     assert_eq!(err, Error::DuplicatedIdentifier);
 
+    // Check incorrect number of identifiers
+
+    let identifiers: Vec<frost::Identifier<C>> = [1u16, 42, 100, 257]
+        .into_iter()
+        .map(|i| i.try_into().unwrap())
+        .collect();
+    let max_signers = 5;
+    let min_signers = 3;
+    let err = frost::keys::generate_with_dealer(
+        max_signers,
+        min_signers,
+        frost::keys::IdentifierList::Custom(&identifiers),
+        &mut rng,
+    )
+    .unwrap_err();
+    assert_eq!(err, Error::IncorrectNumberOfIdentifiers);
+
     // Check correct case
 
     let identifiers: Vec<frost::Identifier<C>> = [1u16, 42, 100, 257, 65535]