WIP: refactor to use memguard for secure memory handling

- Add memguard dependency
- Update ReadPassphrase to return LockedBuffer
- Update EncryptWithPassphrase/DecryptWithPassphrase to accept LockedBuffer
- Remove string wrapper functions
- Update all callers to create LockedBuffers at entry points
- Update interfaces and mock implementations

internal/secret/crypto.go

@@ -8,6 +8,7 @@ import (
 	"syscall"
 
 	"filippo.io/age"
+	"github.com/awnumar/memguard"
 	"golang.org/x/term"
 )
 
@@ -63,8 +64,15 @@ func DecryptWithIdentity(data []byte, identity age.Identity) ([]byte, error) {
 }
 
 // EncryptWithPassphrase encrypts data using a passphrase with age's scrypt-based encryption
-func EncryptWithPassphrase(data []byte, passphrase string) ([]byte, error) {
-	recipient, err := age.NewScryptRecipient(passphrase)
+// The passphrase parameter should be a LockedBuffer for secure memory handling
+func EncryptWithPassphrase(data []byte, passphrase *memguard.LockedBuffer) ([]byte, error) {
+	if passphrase == nil {
+		return nil, fmt.Errorf("passphrase buffer is nil")
+	}
+
+	// Get the passphrase string temporarily
+	passphraseStr := passphrase.String()
+	recipient, err := age.NewScryptRecipient(passphraseStr)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create scrypt recipient: %w", err)
 	}
@@ -73,8 +81,15 @@ func EncryptWithPassphrase(data []byte, passphrase string) ([]byte, error) {
 }
 
 // DecryptWithPassphrase decrypts data using a passphrase with age's scrypt-based decryption
-func DecryptWithPassphrase(encryptedData []byte, passphrase string) ([]byte, error) {
-	identity, err := age.NewScryptIdentity(passphrase)
+// The passphrase parameter should be a LockedBuffer for secure memory handling
+func DecryptWithPassphrase(encryptedData []byte, passphrase *memguard.LockedBuffer) ([]byte, error) {
+	if passphrase == nil {
+		return nil, fmt.Errorf("passphrase buffer is nil")
+	}
+
+	// Get the passphrase string temporarily
+	passphraseStr := passphrase.String()
+	identity, err := age.NewScryptIdentity(passphraseStr)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create scrypt identity: %w", err)
 	}
@@ -84,18 +99,19 @@ func DecryptWithPassphrase(encryptedData []byte, passphrase string) ([]byte, err
 
 // ReadPassphrase reads a passphrase securely from the terminal without echoing
 // This version is for unlocking and doesn't require confirmation
-func ReadPassphrase(prompt string) (string, error) {
+// Returns a LockedBuffer containing the passphrase for secure memory handling
+func ReadPassphrase(prompt string) (*memguard.LockedBuffer, error) {
 	// Check if stdin is a terminal
 	if !term.IsTerminal(syscall.Stdin) {
 		// Not a terminal - never read passphrases from piped input for security reasons
-		return "", fmt.Errorf("cannot read passphrase from non-terminal stdin " +
+		return nil, fmt.Errorf("cannot read passphrase from non-terminal stdin " +
 			"(piped input or script). Please set the SB_UNLOCK_PASSPHRASE " +
 			"environment variable or run interactively")
 	}
 
 	// stdin is a terminal, check if stderr is also a terminal for interactive prompting
 	if !term.IsTerminal(syscall.Stderr) {
-		return "", fmt.Errorf("cannot prompt for passphrase: stderr is not a terminal " +
+		return nil, fmt.Errorf("cannot prompt for passphrase: stderr is not a terminal " +
 			"(running in non-interactive mode). Please set the SB_UNLOCK_PASSPHRASE " +
 			"environment variable")
 	}
@@ -104,13 +120,22 @@ func ReadPassphrase(prompt string) (string, error) {
 	fmt.Fprint(os.Stderr, prompt) // Write prompt to stderr, not stdout
 	passphrase, err := term.ReadPassword(syscall.Stdin)
 	if err != nil {
-		return "", fmt.Errorf("failed to read passphrase: %w", err)
+		return nil, fmt.Errorf("failed to read passphrase: %w", err)
 	}
 	fmt.Fprintln(os.Stderr) // Print newline to stderr since ReadPassword doesn't echo
 
 	if len(passphrase) == 0 {
-		return "", fmt.Errorf("passphrase cannot be empty")
+		return nil, fmt.Errorf("passphrase cannot be empty")
 	}
 
-	return string(passphrase), nil
+	// Create a secure buffer and copy the passphrase
+	secureBuffer := memguard.NewBufferFromBytes(passphrase)
+
+	// Clear the original passphrase slice
+	for i := range passphrase {
+		passphrase[i] = 0
+	}
+
+	return secureBuffer, nil
 }
+

internal/secret/keychainunlocker.go

@@ -13,6 +13,7 @@ import (
 
 	"filippo.io/age"
 	"git.eeqj.de/sneak/secret/pkg/agehd"
+	"github.com/awnumar/memguard"
 	"github.com/spf13/afero"
 )
 
@@ -102,7 +103,11 @@ func (k *KeychainUnlocker) GetIdentity() (*age.X25519Identity, error) {
 
 	// Step 5: Decrypt the age private key using the passphrase from keychain
 	Debug("Decrypting age private key with keychain passphrase", "unlocker_id", k.GetID())
-	agePrivKeyData, err := DecryptWithPassphrase(encryptedAgePrivKeyData, keychainData.AgePrivKeyPassphrase)
+	// Create secure buffer for the keychain passphrase
+	passphraseBuffer := memguard.NewBufferFromBytes([]byte(keychainData.AgePrivKeyPassphrase))
+	defer passphraseBuffer.Destroy()
+	
+	agePrivKeyData, err := DecryptWithPassphrase(encryptedAgePrivKeyData, passphraseBuffer)
 	if err != nil {
 		Debug("Failed to decrypt age private key with keychain passphrase", "error", err, "unlocker_id", k.GetID())
 
@@ -116,7 +121,17 @@ func (k *KeychainUnlocker) GetIdentity() (*age.X25519Identity, error) {
 
 	// Step 6: Parse the decrypted age private key
 	Debug("Parsing decrypted age private key", "unlocker_id", k.GetID())
-	ageIdentity, err := age.ParseX25519Identity(string(agePrivKeyData))
+
+	// Create a secure buffer for the private key data
+	agePrivKeyBuffer := memguard.NewBufferFromBytes(agePrivKeyData)
+	defer agePrivKeyBuffer.Destroy()
+
+	// Clear the original private key data
+	for i := range agePrivKeyData {
+		agePrivKeyData[i] = 0
+	}
+
+	ageIdentity, err := age.ParseX25519Identity(agePrivKeyBuffer.String())
 	if err != nil {
 		Debug("Failed to parse age private key", "error", err, "unlocker_id", k.GetID())
 
@@ -342,8 +357,15 @@ func CreateKeychainUnlocker(fs afero.Fs, stateDir string) (*KeychainUnlocker, er
 	}
 
 	// Step 4: Encrypt age private key with the generated passphrase and store on disk
-	agePrivateKeyBytes := []byte(ageIdentity.String())
-	encryptedAgePrivKey, err := EncryptWithPassphrase(agePrivateKeyBytes, agePrivKeyPassphrase)
+	// Create secure buffers for both the private key and passphrase
+	agePrivKeyStr := ageIdentity.String()
+	agePrivKeyBuffer := memguard.NewBufferFromBytes([]byte(agePrivKeyStr))
+	defer agePrivKeyBuffer.Destroy()
+	
+	passphraseBuffer := memguard.NewBufferFromBytes([]byte(agePrivKeyPassphrase))
+	defer passphraseBuffer.Destroy()
+
+	encryptedAgePrivKey, err := EncryptWithPassphrase(agePrivKeyBuffer.Bytes(), passphraseBuffer)
 	if err != nil {
 		return nil, fmt.Errorf("failed to encrypt age private key with passphrase: %w", err)
 	}

internal/secret/passphrase_test.go

@@ -9,6 +9,7 @@ import (
 	"filippo.io/age"
 	"git.eeqj.de/sneak/secret/internal/secret"
 	"git.eeqj.de/sneak/secret/pkg/agehd"
+	"github.com/awnumar/memguard"
 	"github.com/spf13/afero"
 )
 
@@ -76,7 +77,9 @@ func TestPassphraseUnlockerWithRealFS(t *testing.T) {
 	// Test encrypting private key with passphrase
 	t.Run("EncryptPrivateKey", func(t *testing.T) {
 		privKeyData := []byte(agePrivateKey)
-		encryptedPrivKey, err := secret.EncryptWithPassphrase(privKeyData, testPassphrase)
+		passphraseBuffer := memguard.NewBufferFromBytes([]byte(testPassphrase))
+		defer passphraseBuffer.Destroy()
+		encryptedPrivKey, err := secret.EncryptWithPassphrase(privKeyData, passphraseBuffer)
 		if err != nil {
 			t.Fatalf("Failed to encrypt private key: %v", err)
 		}

internal/secret/passphraseunlocker.go

@@ -7,6 +7,7 @@ import (
 	"path/filepath"
 
 	"filippo.io/age"
+	"github.com/awnumar/memguard"
 	"github.com/spf13/afero"
 )
 
@@ -15,16 +16,17 @@ type PassphraseUnlocker struct {
 	Directory  string
 	Metadata   UnlockerMetadata
 	fs         afero.Fs
-	Passphrase string
+	Passphrase *memguard.LockedBuffer // Secure buffer for passphrase
 }
 
 // getPassphrase retrieves the passphrase from memory, environment, or user input
-func (p *PassphraseUnlocker) getPassphrase() (string, error) {
+// Returns a LockedBuffer for secure memory handling
+func (p *PassphraseUnlocker) getPassphrase() (*memguard.LockedBuffer, error) {
 	// First check if we already have the passphrase
-	if p.Passphrase != "" {
+	if p.Passphrase != nil && p.Passphrase.IsAlive() {
 		Debug("Using in-memory passphrase", "unlocker_id", p.GetID())
-
-		return p.Passphrase, nil
+		// Return a copy of the passphrase buffer
+		return memguard.NewBufferFromBytes(p.Passphrase.Bytes()), nil
 	}
 
 	Debug("No passphrase in memory, checking environment")
@@ -32,20 +34,22 @@ func (p *PassphraseUnlocker) getPassphrase() (string, error) {
 	passphraseStr := os.Getenv(EnvUnlockPassphrase)
 	if passphraseStr != "" {
 		Debug("Using passphrase from environment", "unlocker_id", p.GetID())
-
-		return passphraseStr, nil
+		// Convert to secure buffer
+		secureBuffer := memguard.NewBufferFromBytes([]byte(passphraseStr))
+		
+		return secureBuffer, nil
 	}
 
 	Debug("No passphrase in environment, prompting user")
 	// Prompt for passphrase
-	passphraseStr, err := ReadPassphrase("Enter unlock passphrase: ")
+	secureBuffer, err := ReadPassphrase("Enter unlock passphrase: ")
 	if err != nil {
 		Debug("Failed to read passphrase", "error", err, "unlocker_id", p.GetID())
-
-		return "", fmt.Errorf("failed to read passphrase: %w", err)
+		
+		return nil, fmt.Errorf("failed to read passphrase: %w", err)
 	}
 
-	return passphraseStr, nil
+	return secureBuffer, nil
 }
 
 // GetIdentity implements Unlocker interface for passphrase-based unlockers
@@ -55,10 +59,11 @@ func (p *PassphraseUnlocker) GetIdentity() (*age.X25519Identity, error) {
 		slog.String("unlocker_type", p.GetType()),
 	)
 
-	passphraseStr, err := p.getPassphrase()
+	passphraseBuffer, err := p.getPassphrase()
 	if err != nil {
 		return nil, err
 	}
+	defer passphraseBuffer.Destroy()
 
 	// Read encrypted private key of unlocker
 	unlockerPrivPath := filepath.Join(p.Directory, "priv.age")
@@ -79,7 +84,7 @@ func (p *PassphraseUnlocker) GetIdentity() (*age.X25519Identity, error) {
 	Debug("Decrypting unlocker private key with passphrase", "unlocker_id", p.GetID())
 
 	// Decrypt the unlocker private key with passphrase
-	privKeyData, err := DecryptWithPassphrase(encryptedPrivKeyData, passphraseStr)
+	privKeyData, err := DecryptWithPassphrase(encryptedPrivKeyData, passphraseBuffer)
 	if err != nil {
 		Debug("Failed to decrypt unlocker private key", "error", err, "unlocker_id", p.GetID())
 
@@ -93,7 +98,17 @@ func (p *PassphraseUnlocker) GetIdentity() (*age.X25519Identity, error) {
 
 	// Parse the decrypted private key
 	Debug("Parsing decrypted unlocker identity", "unlocker_id", p.GetID())
-	identity, err := age.ParseX25519Identity(string(privKeyData))
+
+	// Create a secure buffer for the private key data
+	privKeyBuffer := memguard.NewBufferFromBytes(privKeyData)
+	defer privKeyBuffer.Destroy()
+
+	// Clear the original private key data
+	for i := range privKeyData {
+		privKeyData[i] = 0
+	}
+
+	identity, err := age.ParseX25519Identity(privKeyBuffer.String())
 	if err != nil {
 		Debug("Failed to parse unlocker private key", "error", err, "unlocker_id", p.GetID())
 
@@ -133,6 +148,11 @@ func (p *PassphraseUnlocker) GetID() string {
 
 // Remove implements Unlocker interface - removes the passphrase unlocker
 func (p *PassphraseUnlocker) Remove() error {
+	// Clean up the passphrase from memory if it exists
+	if p.Passphrase != nil && p.Passphrase.IsAlive() {
+		p.Passphrase.Destroy()
+	}
+
 	// For passphrase unlockers, we just need to remove the directory
 	// No external resources (like keychain items) to clean up
 	if err := p.fs.RemoveAll(p.Directory); err != nil {
@@ -152,7 +172,8 @@ func NewPassphraseUnlocker(fs afero.Fs, directory string, metadata UnlockerMetad
 }
 
 // CreatePassphraseUnlocker creates a new passphrase-protected unlocker
-func CreatePassphraseUnlocker(fs afero.Fs, stateDir string, passphrase string) (*PassphraseUnlocker, error) {
+// The passphrase must be provided as a LockedBuffer for security
+func CreatePassphraseUnlocker(fs afero.Fs, stateDir string, passphrase *memguard.LockedBuffer) (*PassphraseUnlocker, error) {
 	// Get current vault
 	currentVault, err := GetCurrentVault(fs, stateDir)
 	if err != nil {

internal/secret/pgpunlock_test.go

@@ -16,6 +16,7 @@ import (
 	"git.eeqj.de/sneak/secret/internal/secret"
 	"git.eeqj.de/sneak/secret/internal/vault"
 	"git.eeqj.de/sneak/secret/pkg/agehd"
+	"github.com/awnumar/memguard"
 	"github.com/spf13/afero"
 )
 
@@ -270,7 +271,9 @@ Passphrase: ` + testPassphrase + `
 		vlt.Unlock(ltIdentity)
 
 		// Create a passphrase unlocker first (to have current unlocker)
-		passUnlocker, err := vlt.CreatePassphraseUnlocker("test-passphrase")
+		passphraseBuffer := memguard.NewBufferFromBytes([]byte("test-passphrase"))
+		defer passphraseBuffer.Destroy()
+		passUnlocker, err := vlt.CreatePassphraseUnlocker(passphraseBuffer)
 		if err != nil {
 			t.Fatalf("Failed to create passphrase unlocker: %v", err)
 		}

internal/secret/secret.go

@@ -11,6 +11,7 @@ import (
 
 	"filippo.io/age"
 	"git.eeqj.de/sneak/secret/pkg/agehd"
+	"github.com/awnumar/memguard"
 	"github.com/spf13/afero"
 )
 
@@ -21,7 +22,7 @@ type VaultInterface interface {
 	GetName() string
 	GetFilesystem() afero.Fs
 	GetCurrentUnlocker() (Unlocker, error)
-	CreatePassphraseUnlocker(passphrase string) (*PassphraseUnlocker, error)
+	CreatePassphraseUnlocker(passphrase *memguard.LockedBuffer) (*PassphraseUnlocker, error)
 }
 
 // Secret represents a secret in a vault

internal/secret/secret_test.go

@@ -9,6 +9,7 @@ import (
 
 	"filippo.io/age"
 	"git.eeqj.de/sneak/secret/pkg/agehd"
+	"github.com/awnumar/memguard"
 	"github.com/spf13/afero"
 	"github.com/stretchr/testify/require"
 )
@@ -120,7 +121,7 @@ func (m *MockVault) GetCurrentUnlocker() (Unlocker, error) {
 	return nil, nil
 }
 
-func (m *MockVault) CreatePassphraseUnlocker(_ string) (*PassphraseUnlocker, error) {
+func (m *MockVault) CreatePassphraseUnlocker(_ *memguard.LockedBuffer) (*PassphraseUnlocker, error) {
 	return nil, nil
 }
 

internal/secret/version_test.go

@@ -41,6 +41,7 @@ import (
 	"time"
 
 	"filippo.io/age"
+	"github.com/awnumar/memguard"
 	"github.com/spf13/afero"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -74,7 +75,7 @@ func (m *MockVersionVault) GetCurrentUnlocker() (Unlocker, error) {
 	return nil, fmt.Errorf("not implemented in mock")
 }
 
-func (m *MockVersionVault) CreatePassphraseUnlocker(_ string) (*PassphraseUnlocker, error) {
+func (m *MockVersionVault) CreatePassphraseUnlocker(_ *memguard.LockedBuffer) (*PassphraseUnlocker, error) {
 	return nil, fmt.Errorf("not implemented in mock")
 }