Initial commit

Combines the existing frost-rs, dalek-ff-group, and monero-rs repos into 
a monorepo. Makes tweaks necessary as needed. Replaces RedDSA (which was 
going to be stubbed out into a new folder for now) with an offset system 
that voids its need and allows stealth addresses with CLSAG.

sign/monero/tests/frost.rs

@@ -0,0 +1,65 @@
+#![cfg(feature = "multisig")]
+
+use std::rc::Rc;
+
+use rand::rngs::OsRng;
+
+use ff::Field;
+use dalek_ff_group::{ED25519_BASEPOINT_TABLE, Scalar};
+
+use frost::{
+  MultisigParams, MultisigKeys,
+  key_gen,
+  sign::lagrange
+};
+
+use monero_sign::frost::Ed25519;
+
+pub fn generate_keys(t: usize, n: usize) -> (Vec<Rc<MultisigKeys<Ed25519>>>, Scalar) {
+  let mut params = vec![];
+  let mut machines = vec![];
+  let mut commitments = vec![vec![]];
+  for i in 1 ..= n {
+    params.push(
+      MultisigParams::new(t, n, i).unwrap()
+    );
+    machines.push(
+      key_gen::StateMachine::<Ed25519>::new(
+        params[i - 1],
+        "monero-sign-rs test suite".to_string()
+      )
+    );
+    commitments.push(machines[i - 1].generate_coefficients(&mut OsRng).unwrap());
+  }
+
+  let mut secret_shares = vec![];
+  for i in 1 ..= n {
+    secret_shares.push(
+      machines[i - 1].generate_secret_shares(
+        &mut OsRng,
+        commitments
+          .iter()
+          .enumerate()
+          .map(|(idx, commitments)| if idx == i { vec![] } else { commitments.to_vec() })
+          .collect()
+      ).unwrap()
+    );
+  }
+
+  let mut keys = vec![];
+  for i in 1 ..= n {
+    let mut our_secret_shares = vec![vec![]];
+    our_secret_shares.extend(
+      secret_shares.iter().map(|shares| shares[i].clone()).collect::<Vec<Vec<u8>>>()
+    );
+    keys.push(Rc::new(machines[i - 1].complete(our_secret_shares).unwrap().clone()));
+  }
+
+  let mut group_private = Scalar::zero();
+  for i in 0 .. t {
+    group_private += keys[i].secret_share() * lagrange::<Scalar>(i + 1, &(1 ..= t).collect::<Vec<usize>>());
+  }
+  assert_eq!(&ED25519_BASEPOINT_TABLE * group_private, keys[0].group_key());
+
+  (keys, group_private)
+}