diff --git a/internal/service/handlers/authorize.go b/internal/service/handlers/authorize.go
index 5245d66..62b559b 100644
--- a/internal/service/handlers/authorize.go
+++ b/internal/service/handlers/authorize.go
@@ -35,7 +35,8 @@ func Authorize(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 
-		if err := Verifier(r).VerifyProof(new(big.Int).SetBytes(nullifier).String(), &proof); err != nil {
+		if err = Verifier(r).VerifyProof(new(big.Int).SetBytes(nullifier).String(), &proof); err != nil {
+			Log(r).WithError(err).Info("Failed to verify proof")
 			ape.RenderErr(w, problems.Unauthorized())
 			return
 		}
diff --git a/internal/zkp/main.go b/internal/zkp/main.go
index 83fbf1c..44c893d 100644
--- a/internal/zkp/main.go
+++ b/internal/zkp/main.go
@@ -72,12 +72,18 @@ func (v *Verifier) VerifyProof(user string, proof *zkptypes.ZKProof) (err error)
 
 	// no error can appear
 	chal, _ := base64.StdEncoding.DecodeString(challenge.Value)
+	chalDec := new(big.Int).SetBytes(chal).String()
+
+	switch {
+	case proof.PubSignals[NullifierSignalsIndex] != user:
+		return fmt.Errorf("expected user=%s, got %s", user, proof.PubSignals[NullifierSignalsIndex])
+	case proof.PubSignals[EventIDSignalsIndex] != EventID:
+		return fmt.Errorf("expected eventID=%s, got %s", EventID, proof.PubSignals[EventIDSignalsIndex])
+	case proof.PubSignals[EventDataSignalsIndex] != chalDec:
+		return fmt.Errorf("expected challenge=%s, got %s", chalDec, proof.PubSignals[EventDataSignalsIndex])
+	}
 
-	proof.PubSignals[NullifierSignalsIndex] = user
-	proof.PubSignals[EventIDSignalsIndex] = EventID
-	proof.PubSignals[EventDataSignalsIndex] = new(big.Int).SetBytes(chal).String()
-
-	if err := verifier.VerifyGroth16(*proof, verificationKey); err != nil {
+	if err = verifier.VerifyGroth16(*proof, verificationKey); err != nil {
 		return errors.Wrap(err, "failed to verify generated proof")
 	}