also store signatures from single signs

Author: nickfarrow

schnorr_fun/src/blind.rs

@@ -390,14 +390,18 @@ where
     /// Returns a scalar of the unblinded signature
     pub fn sign_single(&mut self, sig_request: SignatureRequest) -> Option<Scalar<Public, Zero>> {
         let secret_nonce = self.use_secret_nonce(sig_request.public_nonce);
-        match secret_nonce {
+        let signature_response = match secret_nonce {
             Some(secret_nonce) => {
                 let sig = s!(secret_nonce + sig_request.blind_challenge * self.secret).public();
-                Some(sig) //.secret().non_zero()
+                Some(sig)
             }
             // Did not expect this nonce
             None => None,
-        }
+        };
+        // Store this signature
+        self.already_signed
+            .insert(sig_request.public_nonce, signature_response);
+        signature_response
     }
 
     /// Sign multiple blind schnorr signatures concurrently once enough have been requested
@@ -430,16 +434,21 @@ where
                 .clone()
                 .into_iter()
                 .enumerate()
-                .map(|(i, sig_req)| {
-                    let sig = self.sign_single(sig_req.clone());
+                .map(|(i, sig_request)| {
+                    let sig = self.sign_single(sig_request.clone());
                     let response = if self.max_sessions > 1 && i as u32 == skip_i {
                         // Maybe don't return the signature
+                        // ⚠ IMPORTANT: Overwrite the stored signature for this nonce
+                        self.already_signed.insert(sig_request.public_nonce, None);
+                        assert!(self
+                            .already_signed
+                            .get(&sig_request.public_nonce)
+                            .expect("history has to have None written for this nonce")
+                            .is_none());
                         None
                     } else {
                         sig
                     };
-                    // Store signature (or None) for this public nonce
-                    self.already_signed.insert(sig_req.public_nonce, response);
                     response
                 })
                 .collect();