Add some registration validation

server/server.go

@@ -90,6 +90,12 @@ func getRegistrationHandler(keyDir keydirectory.RegistrationDirectory) http.Hand
 			return
 		}
 
+		if !isValidKeyType(key) {
+			fmt.Println("Attempted to register invalid key type")
+			http.Error(w, "Invalid key type", 400)
+			return
+		}
+
 		fmt.Printf("Registering key for %s\n", request.UserId)
 
 		keyId, err := keyDir.RegisterKey(key, request.UserId)

server/validation.go

@@ -0,0 +1,17 @@
+package server
+
+import (
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/ed25519"
+	"crypto/rsa"
+)
+
+func isValidKeyType(key crypto.PublicKey) bool {
+	switch key.(type) {
+	case ed25519.PublicKey, *rsa.PublicKey, *ecdsa.PublicKey:
+		return true
+	default:
+		return false
+	}
+}