Give every view a TSIG key that selects it

Each view's match-clients starts with "key jarl-view-NAME" (after
"!key" for the views listed after it), so a query signed with a view's
key lands in that view from any address. The secrets are derived from a
random seed in Jarl's database. The delegation check signs its queries
to this server's own addresses with the key of the zone's view: before,
they got whichever view matched the server's address, usually internal.
jarl view key / GET /views/{id}/key show a key for dig -k (tsig:write,
audited). jarl-view- key names are reserved; the importer drops view
keys from a configuration Jarl wrote.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/render/viewkeys.go

@@ -0,0 +1,84 @@
+package render
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/base64"
+	"strconv"
+	"strings"
+
+	"jarl/internal/model"
+	"jarl/internal/namedconf"
+)
+
+// View keys let Jarl choose a view regardless of where a query comes from:
+// each view gets a TSIG key, and its match-clients starts with that key
+// (after excluding the keys of the views listed after it, so no earlier
+// view takes their queries). Queries signed with a view's key always land
+// in that view. Jarl signs its own checks of this server's addresses with
+// them (a query from this host would otherwise land in whichever view
+// matches this host's address), and you can too: dig -k.
+//
+// The secrets are derived from a random seed kept in Jarl's database
+// (Extras.ViewKeySeed), so they stay the same from one apply to the next
+// and need no storage of their own. They are in keys.conf with the other
+// keys.
+
+// ViewKeyAlgorithm is the view keys' algorithm.
+const ViewKeyAlgorithm = "hmac-sha256"
+
+// ViewKeyName returns the name of a view's key.
+func ViewKeyName(view string) string { return model.ViewKeyName(view) }
+
+// IsViewKey reports whether a key name is a view key's.
+func IsViewKey(name string) bool {
+	return strings.HasPrefix(strings.ToLower(strings.TrimSuffix(name, ".")), model.ViewKeyPrefix)
+}
+
+// ViewKeySecret returns the secret of the key of the view with this ID.
+func ViewKeySecret(seed []byte, viewID int64) string {
+	m := hmac.New(sha256.New, seed)
+	m.Write([]byte("jarl view key " + strconv.FormatInt(viewID, 10)))
+	return base64.StdEncoding.EncodeToString(m.Sum(nil))
+}
+
+// viewKeysOn reports whether view keys are rendered.
+func viewKeysOn(s *model.State, x Extras) bool { return len(x.ViewKeySeed) > 0 && len(s.Views) > 0 }
+
+// renderViewKeys returns the key statements of the views' keys.
+func renderViewKeys(s *model.State, x Extras) string {
+	if !viewKeysOn(s, x) {
+		return ""
+	}
+	var sb strings.Builder
+	sb.WriteString("\n" + commentBlock("//", "View keys: a query signed with one of these always lands in its view.\nJarl signs its own checks of this server with them; dig -k works too."))
+	for _, v := range s.OrderedViews() {
+		sb.WriteString("key " + namedconf.QuoteString(ViewKeyName(v.Name)) + " {\n\talgorithm " + ViewKeyAlgorithm + ";\n\tsecret " + namedconf.QuoteString(ViewKeySecret(x.ViewKeySeed, v.ID)) + ";\n};\n")
+	}
+	return sb.String()
+}
+
+// viewMatchClients returns a view's match-clients with the view keys in
+// front: "!key" for the keys of the views after it, then its own key, then
+// the view's own list ("any" when it has none, which is what an absent
+// match-clients means).
+func viewMatchClients(s *model.State, x Extras, v *model.View) []string {
+	if !viewKeysOn(s, x) {
+		return v.MatchClients
+	}
+	var out []string
+	after := false
+	for _, o := range s.OrderedViews() {
+		if after {
+			out = append(out, "!key "+namedconf.QuoteString(ViewKeyName(o.Name)))
+		}
+		if o.ID == v.ID {
+			after = true
+		}
+	}
+	out = append(out, "key "+namedconf.QuoteString(ViewKeyName(v.Name)))
+	if len(v.MatchClients) == 0 {
+		return append(out, "any")
+	}
+	return append(out, v.MatchClients...)
+}