data: Add scheme and algorithm fields to Key type

Signed-off-by: Lewis Marshall <lewis@lmars.net>
diff --git a/data/types.go b/data/types.go
index fb4be67..8c029a4 100644
--- a/data/types.go
+++ b/data/types.go
@@ -28,8 +28,10 @@
 }
 
 type Key struct {
-	Type  string   `json:"keytype"`
-	Value KeyValue `json:"keyval"`
+	Type       string   `json:"keytype"`
+	Scheme     string   `json:"scheme"`
+	Algorithms []string `json:"keyid_hash_algorithms"`
+	Value      KeyValue `json:"keyval"`
 
 	id     string
 	idOnce sync.Once