Improvements to Yggdrasil demo (#1114)

* Improvements to Yggdrasil demo

* Fix missing copyright

* Fix tie-break

cmd/dendrite-demo-yggdrasil/convert/25519_test.go

@@ -0,0 +1,51 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package convert
+
+import (
+	"bytes"
+	"crypto/ed25519"
+	"encoding/hex"
+	"testing"
+
+	"golang.org/x/crypto/curve25519"
+)
+
+func TestKeyConversion(t *testing.T) {
+	edPub, edPriv, err := ed25519.GenerateKey(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Log("Signing public:", hex.EncodeToString(edPub))
+	t.Log("Signing private:", hex.EncodeToString(edPriv))
+
+	cuPriv := Ed25519PrivateKeyToCurve25519(edPriv)
+	t.Log("Encryption private:", hex.EncodeToString(cuPriv))
+
+	cuPub := Ed25519PublicKeyToCurve25519(edPub)
+	t.Log("Converted encryption public:", hex.EncodeToString(cuPub))
+
+	var realPub, realPriv [32]byte
+	copy(realPriv[:32], cuPriv[:32])
+	curve25519.ScalarBaseMult(&realPub, &realPriv)
+	t.Log("Scalar-multed encryption public:", hex.EncodeToString(realPub[:]))
+
+	if !bytes.Equal(realPriv[:], cuPriv[:]) {
+		t.Fatal("Private keys should be equal (this means the test is broken)")
+	}
+	if !bytes.Equal(realPub[:], cuPub[:]) {
+		t.Fatal("Public keys should be equal")
+	}
+}