Encrypt pages at rest with a key per person

Pages are sealed with AES-256-GCM. Each person's key is derived (HKDF) from a master key in the settings file plus their Authentik issuer and subject. Plain files from earlier versions are read and re-saved encrypted. Mako refuses to open a notebook it cannot decrypt rather than overwrite it.

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

internal/vault/vault_test.go

@@ -0,0 +1,71 @@
+package vault
+
+import (
+	"bytes"
+	"errors"
+	"strings"
+	"testing"
+)
+
+const master = "0123456789abcdef0123456789abcdef"
+
+func must(t *testing.T, m, iss, sub string) *Cipher {
+	t.Helper()
+	c, err := New(m, iss, sub)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return c
+}
+
+func TestRoundTrip(t *testing.T) {
+	c := must(t, master, "https://a/", "alice")
+	plain := []byte("---\ntitle: \"Secret\"\n---\n\ndear diary")
+	sealed := c.Seal(plain, "page-1")
+	if !IsSealed(sealed) || bytes.Contains(sealed, []byte("diary")) || bytes.Contains(sealed, []byte("Secret")) {
+		t.Fatalf("not encrypted: %q", sealed)
+	}
+	got, err := c.Open(sealed, "page-1")
+	if err != nil || !bytes.Equal(got, plain) {
+		t.Fatalf("open: %q %v", got, err)
+	}
+	if bytes.Equal(sealed, c.Seal(plain, "page-1")) {
+		t.Fatal("two seals of the same text must differ")
+	}
+}
+
+func TestWrongKeyNameOrDamage(t *testing.T) {
+	c := must(t, master, "https://a/", "alice")
+	sealed := c.Seal([]byte("hello"), "p1")
+
+	cases := map[string]*Cipher{
+		"another person":     must(t, master, "https://a/", "bob"),
+		"another issuer":     must(t, master, "https://b/", "alice"),
+		"another master key": must(t, strings.Repeat("z", 40), "https://a/", "alice"),
+	}
+	for name, other := range cases {
+		if _, err := other.Open(sealed, "p1"); !errors.Is(err, ErrWrongKey) {
+			t.Errorf("%s: want ErrWrongKey, got %v", name, err)
+		}
+	}
+	if _, err := c.Open(sealed, "p2"); !errors.Is(err, ErrWrongKey) {
+		t.Errorf("a file moved to another page name opened: %v", err)
+	}
+	bad := append([]byte{}, sealed...)
+	bad[len(bad)-1] ^= 1
+	if _, err := c.Open(bad, "p1"); !errors.Is(err, ErrWrongKey) {
+		t.Errorf("a damaged file opened: %v", err)
+	}
+	if _, err := c.Open([]byte("plain text"), "p1"); !errors.Is(err, ErrWrongKey) {
+		t.Errorf("plain text opened: %v", err)
+	}
+}
+
+func TestNewChecks(t *testing.T) {
+	if _, err := New("short", "i", "s"); err == nil {
+		t.Error("a short key was accepted")
+	}
+	if _, err := New(master, "i", ""); err == nil {
+		t.Error("an empty user was accepted")
+	}
+}