Add first party support for k256 and p256 under feature flags

Given the lack of vectors for k256, it's currently a match of the p256 
spec (with a distinct context string), yet p256 is still always used 
when testing.

crypto/frost/src/tests/literal/kp256.rs

@@ -0,0 +1,80 @@
+use rand::rngs::OsRng;
+
+use crate::{
+  Curve,
+  curves::kp256::{KP256Instance, P256},
+  algorithm::Hram,
+  tests::{curve::test_curve, schnorr::test_schnorr, vectors::{Vectors, vectors}}
+};
+
+#[cfg(feature = "k256")]
+use crate::curves::kp256::K256;
+
+#[test]
+fn p256_curve() {
+  test_curve::<_, P256>(&mut OsRng);
+}
+
+#[test]
+fn p256_schnorr() {
+  test_schnorr::<_, P256>(&mut OsRng);
+}
+
+#[derive(Clone)]
+pub struct IetfP256Hram;
+impl Hram<P256> for IetfP256Hram {
+  #[allow(non_snake_case)]
+  fn hram(R: &p256::ProjectivePoint, A: &p256::ProjectivePoint, m: &[u8]) -> p256::Scalar {
+    P256::hash_to_F(
+      &[P256::CONTEXT, b"chal"].concat(),
+      &[&P256::G_to_bytes(R), &P256::G_to_bytes(A), m].concat()
+    )
+  }
+}
+
+#[test]
+fn p256_vectors() {
+  vectors::<P256, IetfP256Hram>(
+    Vectors {
+      threshold: 2,
+      shares: &[
+        "0c9c1a0fe806c184add50bbdcac913dda73e482daf95dcb9f35dbb0d8a9f7731",
+        "8d8e787bef0ff6c2f494ca45f4dad198c6bee01212d6c84067159c52e1863ad5",
+        "0e80d6e8f6192c003b5488ce1eec8f5429587d48cf001541e713b2d53c09d928"
+      ],
+      group_secret: "8ba9bba2e0fd8c4767154d35a0b7562244a4aaf6f36c8fb8735fa48b301bd8de",
+      group_key: "023a309ad94e9fe8a7ba45dfc58f38bf091959d3c99cfbd02b4dc00585ec45ab70",
+
+      msg: "74657374",
+      included: &[1, 3],
+      nonces: &[
+        [
+          "081617b24375e069b39f649d4c4ce2fba6e38b73e7c16759de0b6079a22c4c7e",
+          "4de5fb77d99f03a2491a83a6a4cb91ca3c82a3f34ce94cec939174f47c9f95dd"
+        ],
+        [
+          "d186ea92593f83ea83181b184d41aa93493301ac2bc5b4b1767e94d2db943e38",
+          "486e2ee25a3fbc8e6399d748b077a2755fde99fa85cc24fa647ea4ebf5811a15"
+        ]
+      ],
+      sig_shares: &[
+        "9e4d8865faf8c7b3193a3b35eda3d9e12118447114b1e7d5b4809ea28067f8a9",
+        "b7d094eab6305ae74daeed1acd31abba9ab81f638d38b72c132cb25a5dfae1fc"
+      ],
+      sig: "0342c14c77f9d4ef9b8bd64fb0d7bbfdb9f8216a44e5f7bbe6ac0f3ed5e1a57367".to_owned() +
+        "561e1d51b129229966e92850bad5859bfee96926fad3007cd3f38639e1ffb554"
+    }
+  );
+}
+
+#[cfg(feature = "k256")]
+#[test]
+fn k256_curve() {
+  test_curve::<_, K256>(&mut OsRng);
+}
+
+#[cfg(feature = "k256")]
+#[test]
+fn k256_schnorr() {
+  test_schnorr::<_, K256>(&mut OsRng);
+}