diff --git a/processor/src/key_gen.rs b/processor/src/key_gen.rs
index 40a858b4..ce670db4 100644
--- a/processor/src/key_gen.rs
+++ b/processor/src/key_gen.rs
@@ -267,6 +267,12 @@ impl<C: Coin, D: Db> KeyGen<C, D> {
         let (coin_machine, coin_shares) =
           handle_machine(&mut rng, params, machines.1, &mut commitments_ref);
 
+        for (_, commitments) in commitments_ref {
+          if !commitments.is_empty() {
+            todo!("malicious signer: extra bytes");
+          }
+        }
+
         self.active_share.insert(id.set, (substrate_machine, coin_machine));
 
         let mut shares: HashMap<_, _> =
@@ -354,6 +360,12 @@ impl<C: Coin, D: Db> KeyGen<C, D> {
         let substrate_keys = handle_machine(&mut rng, params, machines.0, &mut shares_ref);
         let coin_keys = handle_machine(&mut rng, params, machines.1, &mut shares_ref);
 
+        for (_, shares) in shares_ref {
+          if !shares.is_empty() {
+            todo!("malicious signer: extra bytes");
+          }
+        }
+
         let mut coin_keys = ThresholdKeys::new(coin_keys);
         C::tweak_keys(&mut coin_keys);
 
diff --git a/processor/src/signer.rs b/processor/src/signer.rs
index 3e6fb41a..85804fa5 100644
--- a/processor/src/signer.rs
+++ b/processor/src/signer.rs
@@ -374,9 +374,14 @@ impl<C: Coin, D: Db> Signer<C, D> {
         let preprocesses = match preprocesses
           .drain()
           .map(|(l, preprocess)| {
-            machine
-              .read_preprocess::<&[u8]>(&mut preprocess.as_ref())
-              .map(|preprocess| (l, preprocess))
+            let mut preprocess_ref = preprocess.as_ref();
+            let res = machine
+              .read_preprocess::<&[u8]>(&mut preprocess_ref)
+              .map(|preprocess| (l, preprocess));
+            if !preprocess_ref.is_empty() {
+              todo!("malicious signer: extra bytes");
+            }
+            res
           })
           .collect::<Result<_, _>>()
         {
@@ -424,7 +429,12 @@ impl<C: Coin, D: Db> Signer<C, D> {
         let shares = match shares
           .drain()
           .map(|(l, share)| {
-            machine.read_share::<&[u8]>(&mut share.as_ref()).map(|share| (l, share))
+            let mut share_ref = share.as_ref();
+            let res = machine.read_share::<&[u8]>(&mut share_ref).map(|share| (l, share));
+            if !share_ref.is_empty() {
+              todo!("malicious signer: extra bytes");
+            }
+            res
           })
           .collect::<Result<_, _>>()
         {