From 0819612f810a55ebc62301ce4240c887faff8985 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?David=20N=C3=BA=C3=B1ez?= <david@nucypher.com>
Date: Mon, 20 May 2024 13:47:06 +0200
Subject: [PATCH] Method to refresh an AggregateTranscript

---
 ferveo/src/pvss.rs | 49 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/ferveo/src/pvss.rs b/ferveo/src/pvss.rs
index 903c4b62..b9082c6a 100644
--- a/ferveo/src/pvss.rs
+++ b/ferveo/src/pvss.rs
@@ -373,6 +373,55 @@ impl<E: Pairing, T: Aggregate> PubliclyVerifiableSS<E, T> {
             )
     }
 
+    pub fn refresh(
+        &self,
+        update_transcripts: &HashMap<u32, UpdateTranscript<E>>,
+        validator_keys_map: &HashMap<u32, E::G2>,
+    ) -> Result<Self> {
+        let num_shares = self.shares.len();
+        let fft_domain =
+            ark_poly::GeneralEvaluationDomain::<E::ScalarField>::new(
+                num_shares,
+            )
+            .unwrap();
+
+        // First, verify that all update transcript are valid
+        // TODO: Consider what to do with failed verifications
+        // TODO: Find a better way to ensure they're always validated
+        for update_transcript in update_transcripts.values() {
+            update_transcript
+                .verify_refresh(validator_keys_map, &fft_domain)
+                .unwrap();
+        }
+
+        // Participants refresh their shares with the updates from each other:
+        // TODO: Here we're just iterating over all current shares,
+        //       implicitly assuming all of them will be refreshed.
+        //       Generalize to allow refreshing just a subset of the shares.
+        let updated_blinded_shares : Vec<E::G2Affine>= self.shares.iter().enumerate().map(
+            |(index, share)|{
+                let blinded_key_share = ferveo_tdec::BlindedKeyShare{
+                        blinded_key_share: *share,
+                        validator_public_key: validator_keys_map.get(&(index as u32)).unwrap().into_affine()
+                    };
+                let updated_share = UpdatableBlindedKeyShare(blinded_key_share)
+                    .apply_share_updates(
+                        &update_transcripts,
+                        index as u32,
+                    );
+                updated_share.0.blinded_key_share
+            }
+        ).collect();
+
+        let refresed_aggregate_transcript = Self {
+            coeffs: self.coeffs.clone(),
+            shares: updated_blinded_shares,
+            sigma: self.sigma,
+            phantom: Default::default(),
+        };
+
+        Ok(refresed_aggregate_transcript)
+    }
 }
 
 #[derive(Serialize, Deserialize, Clone, Debug, PartialEq, Eq)]