Implement "gocryptfs --passwd" (pasword changing)

cryptfs/config_file.go

@@ -7,15 +7,12 @@ import (
 import "os"
 
 const (
-	// Changing this string breaks backward compatability
-	testBlockData = "gocryptfs test block"
-
 	// The dot "." is not used in base64url (RFC4648), hence
 	// we can never clash with an encrypted file.
 	ConfDefaultName = "gocryptfs.conf"
 )
 
-type confFile struct {
+type ConfFile struct {
 	// File the config is saved to. Not exported to JSON.
 	filename string
 	// Encrypted AES key, unlocked using a password hashed with scrypt
@@ -27,19 +24,14 @@ type confFile struct {
 // CreateConfFile - create a new config with a random key encrypted with
 // "password" and write it to "filename"
 func CreateConfFile(filename string, password string) error {
-	var cf confFile
+	var cf ConfFile
 	cf.filename = filename
 
 	// Generate new random master key
 	key := RandBytes(KEY_LEN)
 
-	// Generate derived key from password
-	cf.ScryptObject = NewScryptKdf()
-	scryptHash := cf.ScryptObject.DeriveKey(password)
-
-	// Lock master key using password-based key
-	cfs := NewCryptFS(scryptHash, false)
-	cf.EncryptedKey = cfs.EncryptBlock(key, 0)
+	// Encrypt it using the password
+	cf.EncryptKey(key, password)
 
 	// Write file to disk
 	err := cf.WriteFile()
@@ -49,21 +41,21 @@ func CreateConfFile(filename string, password string) error {
 
 // LoadConfFile - read config file from disk and decrypt the
 // contained key using password
-func LoadConfFile(filename string, password string) ([]byte, error) {
-	var cf confFile
+func LoadConfFile(filename string, password string) ([]byte, *ConfFile, error) {
+	var cf ConfFile
 	cf.filename = filename
 
 	// Read from disk
 	js, err := ioutil.ReadFile(filename)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
 	// Unmarshal
 	err = json.Unmarshal(js, &cf)
 	if err != nil {
 		Warn.Printf("Failed to unmarshal config file\n")
-		return nil, err
+		return nil, nil, err
 	}
 
 	// Generate derived key from password
@@ -76,15 +68,27 @@ func LoadConfFile(filename string, password string) ([]byte, error) {
 	key, err := cfs.DecryptBlock(cf.EncryptedKey, 0)
 	if err != nil {
 		Warn.Printf("Failed to unlock master key: %s\n", err.Error())
-		return nil, err
+		return nil, nil, err
 	}
 
-	return key, nil
+	return key, &cf, nil
+}
+
+// EncryptKey - encrypt "key" using an scrypt hash generated from "password"
+// and store it in cf.EncryptedKey
+func (cf *ConfFile) EncryptKey(key []byte, password string) {
+	// Generate derived key from password
+	cf.ScryptObject = NewScryptKdf()
+	scryptHash := cf.ScryptObject.DeriveKey(password)
+
+	// Lock master key using password-based key
+	cfs := NewCryptFS(scryptHash, false)
+	cf.EncryptedKey = cfs.EncryptBlock(key, 0)
 }
 
 // WriteFile - write out config in JSON format to file "filename.tmp"
 // then rename over "filename"
-func (cf *confFile) WriteFile() error {
+func (cf *ConfFile) WriteFile() error {
 	tmp := cf.filename + ".tmp"
 	fd, err := os.Create(tmp)
 	if err != nil {

cryptfs/log.go

@@ -30,6 +30,10 @@ func (l *logChannel) Enable() {
 	l.enabled = true
 }
 
+func (l *logChannel) Disable() {
+	l.enabled = false
+}
+
 // Only actually calculate the md5sum if the log channel is enabled to save
 // CPU cycles
 func (l *logChannel) Md5sum(buf []byte) string {

gocryptfs_main/main.go

@@ -13,8 +13,6 @@ import (
 	"github.com/rfjakob/gocryptfs/cryptfs"
 	"github.com/rfjakob/gocryptfs/pathfs_frontend"
 
-	"golang.org/x/crypto/ssh/terminal"
-
 	"github.com/hanwen/go-fuse/fuse"
 	"github.com/hanwen/go-fuse/fuse/nodefs"
 	"github.com/hanwen/go-fuse/fuse/pathfs"
@@ -62,7 +60,7 @@ func main() {
 	runtime.GOMAXPROCS(4)
 
 	// Parse command line arguments
-	var debug, init, zerokey, fusedebug, openssl bool
+	var debug, init, zerokey, fusedebug, openssl, passwd bool
 	var masterkey string
 
 	flag.BoolVar(&debug, "debug", false, "Enable debug output")
@@ -70,6 +68,7 @@ func main() {
 	flag.BoolVar(&init, "init", false, "Initialize encrypted directory")
 	flag.BoolVar(&zerokey, "zerokey", false, "Use all-zero dummy master key")
 	flag.BoolVar(&openssl, "openssl", true, "Use OpenSSL instead of built-in Go crypto")
+	flag.BoolVar(&passwd, "passwd", false, "Change password")
 	flag.StringVar(&masterkey, "masterkey", "", "Mount with explicit master key")
 	var cpuprofile = flag.String("cpuprofile", "", "Write cpu profile to specified file")
 
@@ -97,8 +96,12 @@ func main() {
 			os.Exit(ERREXIT_USAGE)
 		}
 		initDir(flag.Arg(0))
-	}
-	if flag.NArg() < 2 {
+	} else if passwd {
+		if flag.NArg() != 1 {
+			fmt.Printf("usage: %s --passwd CIPHERDIR\n", PROGRAM_NAME)
+			os.Exit(ERREXIT_USAGE)
+		}
+	} else if flag.NArg() < 2 {
 		fmt.Printf("usage: %s [OPTIONS] CIPHERDIR MOUNTPOINT\n", PROGRAM_NAME)
 		os.Exit(ERREXIT_USAGE)
 	}
@@ -112,6 +115,8 @@ func main() {
 		os.Exit(ERREXIT_CIPHERDIR)
 	}
 
+	var cf *cryptfs.ConfFile
+	var currentPassword string
 	key := make([]byte, cryptfs.KEY_LEN)
 	if zerokey {
 		fmt.Printf("Zerokey mode active: using all-zero dummy master key.\n")
@@ -126,16 +131,39 @@ func main() {
 			fmt.Printf("Please run \"%s --init %s\" first\n", PROGRAM_NAME, flag.Arg(0))
 			os.Exit(ERREXIT_LOADCONF)
 		}
-		fmt.Printf("Password: ")
-		password := readPassword()
+		if passwd == true {
+			fmt.Printf("Old password: ")
+		} else {
+			fmt.Printf("Password: ")
+		}
+		currentPassword = readPassword()
 		fmt.Printf("\nDecrypting master key... ")
-		key, err = cryptfs.LoadConfFile(cfname, password)
+		cryptfs.Warn.Disable() // Silence DecryptBlock() error messages on incorrect password
+		key, cf, err = cryptfs.LoadConfFile(cfname, currentPassword)
+		cryptfs.Warn.Enable()
 		if err != nil {
 			fmt.Println(err)
+			fmt.Println("Password incorrect.")
 			os.Exit(ERREXIT_LOADCONF)
 		}
 		fmt.Printf("done.\n")
 	}
+	if passwd == true {
+		fmt.Printf("Please enter the new password.\n")
+		newPassword := readPasswordTwice()
+		if newPassword == currentPassword {
+			fmt.Printf("New and old passwords are identical\n")
+			os.Exit(1)
+		}
+		cf.EncryptKey(key, newPassword)
+		err := cf.WriteFile()
+		if err != nil {
+			fmt.Println(err)
+			os.Exit(ERREXIT_INIT)
+		}
+		fmt.Printf("Password changed.\n")
+		os.Exit(0)
+	}
 
 	srv := pathfsFrontend(key, cipherdir, mountpoint, fusedebug, openssl)
 	fmt.Printf("Mounted.\n")
@@ -154,30 +182,6 @@ func main() {
 	srv.Serve()
 }
 
-func readPasswordTwice() string {
-	fmt.Printf("Password: ")
-	p1 := readPassword()
-	fmt.Printf("\nRepeat: ")
-	p2 := readPassword()
-	fmt.Printf("\n")
-	if p1 != p2 {
-		fmt.Printf("Passwords do not match\n")
-		os.Exit(ERREXIT_PASSWORD)
-	}
-	return p1
-}
-
-// Get password from terminal
-func readPassword() string {
-	fd := int(os.Stdin.Fd())
-	p, err := terminal.ReadPassword(fd)
-	if err != nil {
-		fmt.Printf("Error: Could not read password: %v\n", err)
-		os.Exit(ERREXIT_PASSWORD)
-	}
-	return string(p)
-}
-
 func dirEmpty(dir string) bool {
 	entries, err := ioutil.ReadDir(dir)
 	if err != nil {

gocryptfs_main/password.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"fmt"
+	"golang.org/x/crypto/ssh/terminal"
+	"os"
+)
+
+func readPasswordTwice() string {
+	fmt.Printf("Password: ")
+	p1 := readPassword()
+	fmt.Printf("\nRepeat: ")
+	p2 := readPassword()
+	fmt.Printf("\n")
+	if p1 != p2 {
+		fmt.Printf("Passwords do not match\n")
+		os.Exit(ERREXIT_PASSWORD)
+	}
+	return p1
+}
+
+// Get password from terminal
+func readPassword() string {
+	fd := int(os.Stdin.Fd())
+	p, err := terminal.ReadPassword(fd)
+	if err != nil {
+		fmt.Printf("Error: Could not read password: %v\n", err)
+		os.Exit(ERREXIT_PASSWORD)
+	}
+	return string(p)
+}