add another functional test

tests/frost.rs

@@ -99,3 +99,44 @@ fn check_sign_with_dealer_randomized() {
         .verify(&message, &group_signature)
         .is_ok());
 }
+
+#[test]
+fn check_sign_with_dealer_fails_with_unintended_randomized() {
+    let mut rng = thread_rng();
+    let numsigners = 5;
+    let threshold = 3;
+    let (shares, pubkeys) = keygen_with_dealer(numsigners, threshold, &mut rng).unwrap();
+
+    let mut nonces: HashMap<u32, Vec<SigningNonces>> = HashMap::with_capacity(threshold as usize);
+    let mut commitments: Vec<SigningCommitments> = Vec::with_capacity(threshold as usize);
+
+    for participant_index in 1..(threshold + 1) {
+        let (nonce, commitment) = preprocess(1, participant_index, &mut rng);
+        nonces.insert(participant_index, nonce);
+        commitments.push(commitment[0]);
+    }
+
+    let mut signature_shares: Vec<SignatureShare> = Vec::with_capacity(threshold as usize);
+    let message = "message to sign".as_bytes();
+    let signing_package = SigningPackage {
+        message,
+        signing_commitments: commitments,
+        randomized: false,
+    };
+    for (participant_index, nonce) in nonces {
+        let share_package = shares
+            .iter()
+            .find(|share| participant_index == share.index)
+            .unwrap();
+        let nonce_to_use = &nonce[0];
+        let signature_share = sign(&signing_package, &nonce_to_use, share_package).unwrap();
+        signature_shares.push(signature_share);
+    }
+
+    let randomized_pubkeys = pubkeys.randomize(&signing_package).unwrap();
+
+    // make sure that using randomized public keys unintentionally results
+    // in an invalid signature
+    let group_signature_res = aggregate(&signing_package, &signature_shares, &randomized_pubkeys);
+    assert!(!group_signature_res.is_ok());
+}