derp: move away from [32]byte key types

And some minor cleanup in the process.

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

derp/derphttp/derphttp_test.go

@@ -5,7 +5,7 @@
 package derphttp
 
 import (
-	"crypto/rand"
+	crand "crypto/rand"
 	"crypto/tls"
 	"net"
 	"net/http"
@@ -13,29 +13,27 @@ import (
 	"testing"
 	"time"
 
-	"golang.org/x/crypto/curve25519"
 	"tailscale.com/derp"
+	"tailscale.com/types/key"
 )
 
 func TestSendRecv(t *testing.T) {
 	const numClients = 3
-	var serverPrivateKey [32]byte
-	if _, err := rand.Read(serverPrivateKey[:]); err != nil {
+	var serverPrivateKey key.Private
+	if _, err := crand.Read(serverPrivateKey[:]); err != nil {
 		t.Fatal(err)
 	}
-	var clientPrivateKeys [][32]byte
+	var clientPrivateKeys []key.Private
 	for i := 0; i < numClients; i++ {
-		var key [32]byte
-		if _, err := rand.Read(key[:]); err != nil {
+		var key key.Private
+		if _, err := crand.Read(key[:]); err != nil {
 			t.Fatal(err)
 		}
 		clientPrivateKeys = append(clientPrivateKeys, key)
 	}
-	var clientKeys [][32]byte
+	var clientKeys []key.Public
 	for _, privKey := range clientPrivateKeys {
-		var key [32]byte
-		curve25519.ScalarBaseMult(&key, &privKey)
-		clientKeys = append(clientKeys, key)
+		clientKeys = append(clientKeys, privKey.Public())
 	}
 
 	s := derp.NewServer(serverPrivateKey, t.Logf)