Step 19: Encryption CLI, slot management, proto updates.

CLI: sgard encrypt init [--fido2], add-fido2 [--label], remove-slot,
list-slots, change-passphrase. sgard add --encrypt flag with
passphrase prompt for DEK unlock.

Garden: RemoveSlot (refuses last slot), ListSlots, ChangePassphrase
(re-wraps DEK with new passphrase, fresh salt).

Proto: ManifestEntry gains encrypted + plaintext_hash fields. New
KekSlot and Encryption messages. Manifest gains encryption field.

server/convert.go: full round-trip conversion for encryption section
including KekSlot map.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd/sgard/add.go

@@ -1,12 +1,17 @@
 package main
 
 import (
+	"bufio"
 	"fmt"
+	"os"
+	"strings"
 
 	"github.com/kisom/sgard/garden"
 	"github.com/spf13/cobra"
 )
 
+var encryptFlag bool
+
 var addCmd = &cobra.Command{
 	Use:   "add <path>...",
 	Short: "Track files, directories, or symlinks",
@@ -17,7 +22,16 @@ var addCmd = &cobra.Command{
 			return err
 		}
 
-		if err := g.Add(args); err != nil {
+		if encryptFlag {
+			if !g.HasEncryption() {
+				return fmt.Errorf("encryption not initialized; run sgard encrypt init first")
+			}
+			if err := g.UnlockDEK(promptPassphrase); err != nil {
+				return err
+			}
+		}
+
+		if err := g.Add(args, encryptFlag); err != nil {
 			return err
 		}
 
@@ -26,6 +40,16 @@ var addCmd = &cobra.Command{
 	},
 }
 
+func promptPassphrase() (string, error) {
+	fmt.Fprint(os.Stderr, "Passphrase: ")
+	scanner := bufio.NewScanner(os.Stdin)
+	if scanner.Scan() {
+		return strings.TrimSpace(scanner.Text()), nil
+	}
+	return "", fmt.Errorf("no passphrase provided")
+}
+
 func init() {
+	addCmd.Flags().BoolVar(&encryptFlag, "encrypt", false, "encrypt file contents before storing")
 	rootCmd.AddCommand(addCmd)
 }

cmd/sgard/encrypt.go

@@ -0,0 +1,166 @@
+package main
+
+import (
+	"fmt"
+	"sort"
+
+	"github.com/kisom/sgard/garden"
+	"github.com/spf13/cobra"
+)
+
+var encryptCmd = &cobra.Command{
+	Use:   "encrypt",
+	Short: "Manage encryption keys and slots",
+}
+
+var fido2InitFlag bool
+
+var encryptInitCmd = &cobra.Command{
+	Use:   "init",
+	Short: "Initialize encryption (creates DEK and passphrase slot)",
+	RunE: func(cmd *cobra.Command, args []string) error {
+		g, err := garden.Open(repoFlag)
+		if err != nil {
+			return err
+		}
+
+		passphrase, err := promptPassphrase()
+		if err != nil {
+			return err
+		}
+
+		if err := g.EncryptInit(passphrase); err != nil {
+			return err
+		}
+
+		fmt.Println("Encryption initialized with passphrase slot.")
+
+		if fido2InitFlag {
+			fmt.Println("FIDO2 support requires a hardware device implementation.")
+			fmt.Println("Run 'sgard encrypt add-fido2' when a FIDO2 device is available.")
+		}
+
+		return nil
+	},
+}
+
+var fido2LabelFlag string
+
+var addFido2Cmd = &cobra.Command{
+	Use:   "add-fido2",
+	Short: "Add a FIDO2 KEK slot",
+	RunE: func(cmd *cobra.Command, args []string) error {
+		g, err := garden.Open(repoFlag)
+		if err != nil {
+			return err
+		}
+
+		if !g.HasEncryption() {
+			return fmt.Errorf("encryption not initialized; run sgard encrypt init first")
+		}
+
+		if err := g.UnlockDEK(promptPassphrase); err != nil {
+			return err
+		}
+
+		// Real FIDO2 device implementation would go here.
+		// For now, this is a placeholder that explains the requirement.
+		return fmt.Errorf("FIDO2 hardware support not yet implemented; requires libfido2 binding")
+	},
+}
+
+var removeSlotCmd = &cobra.Command{
+	Use:   "remove-slot <name>",
+	Short: "Remove a KEK slot",
+	Args:  cobra.ExactArgs(1),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		g, err := garden.Open(repoFlag)
+		if err != nil {
+			return err
+		}
+
+		if err := g.RemoveSlot(args[0]); err != nil {
+			return err
+		}
+
+		fmt.Printf("Removed slot %q.\n", args[0])
+		return nil
+	},
+}
+
+var listSlotsCmd = &cobra.Command{
+	Use:   "list-slots",
+	Short: "List all KEK slots",
+	RunE: func(cmd *cobra.Command, args []string) error {
+		g, err := garden.Open(repoFlag)
+		if err != nil {
+			return err
+		}
+
+		slots := g.ListSlots()
+		if len(slots) == 0 {
+			fmt.Println("No encryption configured.")
+			return nil
+		}
+
+		// Sort for consistent output.
+		names := make([]string, 0, len(slots))
+		for name := range slots {
+			names = append(names, name)
+		}
+		sort.Strings(names)
+
+		for _, name := range names {
+			fmt.Printf("%-30s %s\n", name, slots[name])
+		}
+		return nil
+	},
+}
+
+var changePassphraseCmd = &cobra.Command{
+	Use:   "change-passphrase",
+	Short: "Change the passphrase for the passphrase KEK slot",
+	RunE: func(cmd *cobra.Command, args []string) error {
+		g, err := garden.Open(repoFlag)
+		if err != nil {
+			return err
+		}
+
+		if !g.HasEncryption() {
+			return fmt.Errorf("encryption not initialized")
+		}
+
+		// Unlock with current passphrase.
+		fmt.Println("Enter current passphrase:")
+		if err := g.UnlockDEK(promptPassphrase); err != nil {
+			return err
+		}
+
+		// Get new passphrase.
+		fmt.Println("Enter new passphrase:")
+		newPassphrase, err := promptPassphrase()
+		if err != nil {
+			return err
+		}
+
+		if err := g.ChangePassphrase(newPassphrase); err != nil {
+			return err
+		}
+
+		fmt.Println("Passphrase changed.")
+		return nil
+	},
+}
+
+func init() {
+	encryptInitCmd.Flags().BoolVar(&fido2InitFlag, "fido2", false, "also set up FIDO2 (placeholder)")
+	addFido2Cmd.Flags().StringVar(&fido2LabelFlag, "label", "", "slot label (default: fido2/<hostname>)")
+
+	encryptCmd.AddCommand(encryptInitCmd)
+	encryptCmd.AddCommand(addFido2Cmd)
+	encryptCmd.AddCommand(removeSlotCmd)
+	encryptCmd.AddCommand(listSlotsCmd)
+	encryptCmd.AddCommand(changePassphraseCmd)
+
+	rootCmd.AddCommand(encryptCmd)
+}