Simplify Monero key image handling

crypto/dalek-ff-group/src/lib.rs

@@ -13,7 +13,7 @@ pub use curve25519_dalek as dalek;
 
 use dalek::{
   constants,
-  traits::Identity,
+  traits::{Identity, IsIdentity},
   scalar::Scalar as DScalar,
   edwards::{
     EdwardsPoint as DPoint,
@@ -248,7 +248,7 @@ impl Group for EdwardsPoint {
   fn random(mut _rng: impl RngCore) -> Self { unimplemented!() }
   fn identity() -> Self { Self(DPoint::identity()) }
   fn generator() -> Self { ED25519_BASEPOINT_POINT }
-  fn is_identity(&self) -> Choice { unimplemented!() }
+  fn is_identity(&self) -> Choice { (self.0.is_identity() as u8).into() }
   fn double(&self) -> Self { *self + self }
 }
 

crypto/frost/src/algorithm.rs

@@ -18,6 +18,7 @@ pub trait Algorithm<C: Curve>: Clone {
 
   /// Generate an addendum to FROST"s preprocessing stage
   fn preprocess_addendum<R: RngCore + CryptoRng>(
+    &mut self,
     rng: &mut R,
     params: &MultisigView<C>,
     nonces: &[C::F; 2],
@@ -119,6 +120,7 @@ impl<C: Curve, H: Hram<C>> Algorithm<C> for Schnorr<C, H> {
   }
 
   fn preprocess_addendum<R: RngCore + CryptoRng>(
+    &mut self,
     _: &mut R,
     _: &MultisigView<C>,
     _: &[C::F; 2],

crypto/frost/src/sign.rs

@@ -104,7 +104,7 @@ fn preprocess<R: RngCore + CryptoRng, C: Curve, A: Algorithm<C>>(
   serialized.extend(&C::G_to_bytes(&commitments[1]));
 
   serialized.extend(
-    &A::preprocess_addendum(
+    &params.algorithm.preprocess_addendum(
       rng,
       &params.view,
       &nonces