tka,types/key: implement direct node-key signatures

Signed-off-by: Tom DNetto <tom@tailscale.com>

tka/sig_test.go

@@ -0,0 +1,34 @@
+// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tka
+
+import (
+	"crypto/ed25519"
+	"testing"
+)
+
+func TestSigDirect(t *testing.T) {
+	nodeKeyPub := []byte{1, 2, 3, 4}
+
+	// Verification key (the key used to sign)
+	pub, priv := testingKey25519(t, 1)
+	key := Key{Kind: Key25519, Public: pub, Votes: 2}
+
+	sig := NodeKeySignature{
+		SigKind: SigDirect,
+		KeyID:   key.ID(),
+		Pubkey:  nodeKeyPub,
+	}
+	sigHash := sig.sigHash()
+	sig.Signature = ed25519.Sign(priv, sigHash[:])
+
+	if sig.sigHash() != sigHash {
+		t.Errorf("sigHash changed after signing: %x != %x", sig.sigHash(), sigHash)
+	}
+
+	if err := sig.verifySignature(key); err != nil {
+		t.Fatalf("verifySignature() failed: %v", err)
+	}
+}