Finish implementing FROST v5

Identity check for P256 and H4 was all that was needed.

coins/monero/src/frost.rs

@@ -11,7 +11,7 @@ use curve25519_dalek::{
   edwards::EdwardsPoint as DPoint
 };
 
-use ff::PrimeField;
+use ff::{Field, PrimeField};
 use group::Group;
 
 use transcript::{Transcript as TranscriptTrait, DigestTranscript};
@@ -59,6 +59,10 @@ impl Curve for Ed25519 {
     true
   }
 
+  fn random_nonce<R: RngCore + CryptoRng>(_secret: Self::F, rng: &mut R) -> Self::F {
+    dfg::Scalar::random(rng)
+  }
+
   // This will already be a keccak256 hash in the case of CLSAG signing, making it fine to simply
   // return as-is, yet this ensures it's fixed size (a security requirement) and unique regardless
   // of how it's called/what it's called with