change GroupCommitment to use AffinePoint

src/frost.rs

@@ -92,7 +92,7 @@ pub struct ShareCommitment(Vec<Commitment>);
 
 /// The product of all signers' individual commitments, published as part of the
 /// final signature.
-pub struct GroupCommitment(jubjub::ExtendedPoint);
+pub struct GroupCommitment(jubjub::AffinePoint);
 
 /// Secret and public key material generated by a dealer performing
 /// [`keygen_with_dealer`].
@@ -503,7 +503,7 @@ fn gen_group_commitment(
         accumulator += commitment.hiding + (commitment.binding * rho_i)
     }
 
-    Ok(GroupCommitment(accumulator))
+    Ok(GroupCommitment(jubjub::AffinePoint::from(accumulator)))
 }
 
 /// Generates the challenge as is required for Schnorr signatures.