trezor: add skeleton for Trezor support

readpassword.Trezor() is not implemented yet and returns
a hardcoded dummy key.

10 files changed, 86 insertions, 26 deletions

diff --git a/cli_args.go b/cli_args.go
index 08b3186..7e8deeb 100644
--- a/cli_args.go
+++ b/cli_args.go
@@ -22,7 +22,7 @@ type argContainer struct {
 	plaintextnames, quiet, nosyslog, wpanic,
 	longnames, allow_other, reverse, aessiv, nonempty, raw64,
 	noprealloc, speed, hkdf, serialize_reads, forcedecode, hh, info,
-	sharedstorage, devrandom, fsck bool
+	sharedstorage, devrandom, fsck, trezor bool
 	// Mount options with opposites
 	dev, nodev, suid, nosuid, exec, noexec, rw, ro bool
 	masterkey, mountpoint, cipherdir, cpuprofile, extpass,
@@ -138,6 +138,7 @@ func parseCliOpts() (args argContainer) {
 	flagSet.BoolVar(&args.sharedstorage, "sharedstorage", false, "Make concurrent access to a shared CIPHERDIR safer")
 	flagSet.BoolVar(&args.devrandom, "devrandom", false, "Use /dev/random for generating master key")
 	flagSet.BoolVar(&args.fsck, "fsck", false, "Run a filesystem check on CIPHERDIR")
+	flagSet.BoolVar(&args.trezor, "trezor", false, "Protect the masterkey using a SatoshiLabs Trezor instead of a password")
 
 	// Mount options with opposites
 	flagSet.BoolVar(&args.dev, "dev", false, "Allow device files")
diff --git a/init_dir.go b/init_dir.go
index 0e1ad95..ea6fff4 100644
--- a/init_dir.go
+++ b/init_dir.go
@@ -43,11 +43,12 @@ func isDir(dir string) error {
 	return nil
 }
 
-// initDir prepares a directory for use as a gocryptfs storage directory.
+// initDir handles "gocryptfs -init". It prepares a directory for use as a
+// gocryptfs storage directory.
 // In forward mode, this means creating the gocryptfs.conf and gocryptfs.diriv
 // files in an empty directory.
 // In reverse mode, we create .gocryptfs.reverse.conf and the directory does
-// not to be empty.
+// not need to be empty.
 func initDir(args *argContainer) {
 	var err error
 	if args.reverse {
@@ -68,10 +69,18 @@ func initDir(args *argContainer) {
 		tlog.Info.Printf("Choose a password for protecting your files.")
 	}
 	{
+		var password []byte
+		if args.trezor {
+			// Get binary data from from Trezor
+			password = readpassword.Trezor()
+		} else {
+			// Normal password entry
+			password = readpassword.Twice(args.extpass)
+			readpassword.CheckTrailingGarbage()
+		}
 		creator := tlog.ProgramName + " " + GitVersion
-		password := readpassword.Twice(args.extpass)
-		readpassword.CheckTrailingGarbage()
-		err = configfile.CreateConfFile(args.config, password, args.plaintextnames, args.scryptn, creator, args.aessiv, args.devrandom)
+		err = configfile.CreateConfFile(args.config, password, args.plaintextnames,
+			args.scryptn, creator, args.aessiv, args.devrandom, args.trezor)
 		if err != nil {
 			tlog.Fatal.Println(err)
 			os.Exit(exitcodes.WriteConf)
@@ -81,7 +90,7 @@ func initDir(args *argContainer) {
 		}
 		// password runs out of scope here
 	}
-	// Forward mode with filename encryption enabled needs a gocryptfs.diriv
+	// Forward mode with filename encryption enabled needs a gocryptfs.diriv file
 	// in the root dir
 	if !args.plaintextnames && !args.reverse {
 		err = nametransform.WriteDirIV(nil, args.cipherdir)
diff --git a/internal/configfile/config_file.go b/internal/configfile/config_file.go
index 0d5e545..da6c4da 100644
--- a/internal/configfile/config_file.go
+++ b/internal/configfile/config_file.go
@@ -67,7 +67,8 @@ func randBytesDevRandom(n int) []byte {
 // CreateConfFile - create a new config with a random key encrypted with
 // "password" and write it to "filename".
 // Uses scrypt with cost parameter logN.
-func CreateConfFile(filename string, password []byte, plaintextNames bool, logN int, creator string, aessiv bool, devrandom bool) error {
+func CreateConfFile(filename string, password []byte, plaintextNames bool,
+	logN int, creator string, aessiv bool, devrandom bool, trezor bool) error {
 	var cf ConfFile
 	cf.filename = filename
 	cf.Creator = creator
@@ -87,6 +88,9 @@ func CreateConfFile(filename string, password []byte, plaintextNames bool, logN
 	if aessiv {
 		cf.FeatureFlags = append(cf.FeatureFlags, knownFlags[FlagAESSIV])
 	}
+	if trezor {
+		cf.FeatureFlags = append(cf.FeatureFlags, knownFlags[FlagTrezor])
+	}
 	{
 		// Generate new random master key
 		var key []byte
diff --git a/internal/configfile/config_test.go b/internal/configfile/config_test.go
index 15728c6..3152ab5 100644
--- a/internal/configfile/config_test.go
+++ b/internal/configfile/config_test.go
@@ -62,7 +62,7 @@ func TestLoadV2StrangeFeature(t *testing.T) {
 }
 
 func TestCreateConfDefault(t *testing.T) {
-	err := CreateConfFile("config_test/tmp.conf", testPw, false, 10, "test", false, false)
+	err := CreateConfFile("config_test/tmp.conf", testPw, false, 10, "test", false, false, false)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -83,14 +83,14 @@ func TestCreateConfDefault(t *testing.T) {
 }
 
 func TestCreateConfDevRandom(t *testing.T) {
-	err := CreateConfFile("config_test/tmp.conf", testPw, false, 10, "test", false, true)
+	err := CreateConfFile("config_test/tmp.conf", testPw, false, 10, "test", false, true, false)
 	if err != nil {
 		t.Fatal(err)
 	}
 }
 
 func TestCreateConfPlaintextnames(t *testing.T) {
-	err := CreateConfFile("config_test/tmp.conf", testPw, true, 10, "test", false, false)
+	err := CreateConfFile("config_test/tmp.conf", testPw, true, 10, "test", false, false, false)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -111,7 +111,7 @@ func TestCreateConfPlaintextnames(t *testing.T) {
 
 // Reverse mode uses AESSIV
 func TestCreateConfFileAESSIV(t *testing.T) {
-	err := CreateConfFile("config_test/tmp.conf", testPw, false, 10, "test", true, false)
+	err := CreateConfFile("config_test/tmp.conf", testPw, false, 10, "test", true, false, false)
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/internal/configfile/feature_flags.go b/internal/configfile/feature_flags.go
index 2d609f2..141b007 100644
--- a/internal/configfile/feature_flags.go
+++ b/internal/configfile/feature_flags.go
@@ -25,6 +25,9 @@ const (
 	// Note that this flag does not change the password hashing algorithm
 	// which always is scrypt.
 	FlagHKDF
+	// FlagTrezor means that "-trezor" was used when creating the filesystem.
+	// The masterkey is protected using a Trezor device instead of a password.
+	FlagTrezor
 )
 
 // knownFlags stores the known feature flags and their string representation
@@ -37,6 +40,7 @@ var knownFlags = map[flagIota]string{
 	FlagAESSIV:         "AESSIV",
 	FlagRaw64:          "Raw64",
 	FlagHKDF:           "HKDF",
+	FlagTrezor:         "Trezor",
 }
 
 // Filesystems that do not have these feature flags set are deprecated.
diff --git a/internal/exitcodes/exitcodes.go b/internal/exitcodes/exitcodes.go
index fc65166..3fbfdc6 100644
--- a/internal/exitcodes/exitcodes.go
+++ b/internal/exitcodes/exitcodes.go
@@ -65,6 +65,9 @@ const (
 	FsckErrors = 26
 	// DeprecatedFS - this filesystem is deprecated
 	DeprecatedFS = 27
+	// TrezorError - an error was encountered while interacting with a Trezor
+	// device
+	TrezorError = 28
 )
 
 // Err wraps an error with an associated numeric exit code
diff --git a/internal/readpassword/trezor.go b/internal/readpassword/trezor.go
new file mode 100644
index 0000000..37dde79
--- /dev/null
+++ b/internal/readpassword/trezor.go
@@ -0,0 +1,26 @@
+package readpassword
+
+import (
+	"os"
+
+	"github.com/rfjakob/gocryptfs/internal/exitcodes"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+// Trezor reads 16 deterministically derived bytes from a
+// SatoshiLabs Trezor USB security module.
+// The bytes are pseudorandom binary data and may contain null bytes.
+// This function either succeeds and returns 16 bytes or calls os.Exit to end
+// the application.
+func Trezor() []byte {
+	var err error
+	// TODO try to read bytes here....
+	// Handle errors
+	if err != nil {
+		tlog.Fatal.Printf("xxx some error was encountered...")
+		os.Exit(exitcodes.TrezorError)
+	}
+
+	tlog.Warn.Println("XXX readpassword.Trezor(): not implemented yet - returning hardcoded dummy bytes XXX")
+	return []byte("1234567890123456")
+}
diff --git a/main.go b/main.go
index 226a20a..9fdbc6e 100644
--- a/main.go
+++ b/main.go
@@ -33,26 +33,33 @@ var raceDetector bool
 
 // loadConfig loads the config file "args.config", prompting the user for the password
 func loadConfig(args *argContainer) (masterkey []byte, confFile *configfile.ConfFile, err error) {
-	// Check if the file can be opened at all before prompting for a password
-	fd, err := os.Open(args.config)
+	// First check if the file can be read at all, and find out if a Trezor should
+	// be used instead of a password.
+	_, cf1, err := configfile.LoadConfFile(args.config, nil)
 	if err != nil {
 		tlog.Fatal.Printf("Cannot open config file: %v", err)
-		return nil, nil, exitcodes.NewErr(err.Error(), exitcodes.OpenConf)
+		return nil, nil, err
 	}
-	fd.Close()
-	// The user has passed the master key (probably because he forgot the
-	// password).
+	// The user has passed the master key on the command line (probably because
+	// he forgot the password).
 	if args.masterkey != "" {
 		masterkey = parseMasterKey(args.masterkey, false)
-		_, confFile, err = configfile.LoadConfFile(args.config, nil)
+		return masterkey, cf1, nil
+	}
+	var pw []byte
+	if cf1.IsFeatureFlagSet(configfile.FlagTrezor) {
+		// Get binary data from from Trezor
+		pw = readpassword.Trezor()
 	} else {
-		pw := readpassword.Once(args.extpass, "")
-		tlog.Info.Println("Decrypting master key")
-		masterkey, confFile, err = configfile.LoadConfFile(args.config, pw)
-		for i := range pw {
-			pw[i] = 0
-		}
+		// Normal password entry
+		pw = readpassword.Once(args.extpass, "")
 	}
+	tlog.Info.Println("Decrypting master key")
+	masterkey, confFile, err = configfile.LoadConfFile(args.config, pw)
+	for i := range pw {
+		pw[i] = 0
+	}
+
 	if err != nil {
 		tlog.Fatal.Println(err)
 		return nil, nil, err
@@ -71,6 +78,9 @@ func changePassword(args *argContainer) {
 		if err != nil {
 			exitcodes.Exit(err)
 		}
+		if len(masterkey) == 0 {
+			panic("empty masterkey")
+		}
 		tlog.Info.Println("Please enter your new password.")
 		newPw := readpassword.Twice(args.extpass)
 		readpassword.CheckTrailingGarbage()
diff --git a/masterkey.go b/masterkey.go
index c67f115..1b4d9c3 100644
--- a/masterkey.go
+++ b/masterkey.go
@@ -103,7 +103,9 @@ func getMasterKey(args *argContainer) (masterkey []byte, confFile *configfile.Co
 		}
 		exitcodes.Exit(err)
 	}
-	readpassword.CheckTrailingGarbage()
+	if !args.trezor {
+		readpassword.CheckTrailingGarbage()
+	}
 	if !args.fsck {
 		// We only want to print the masterkey message on a normal mount.
 		printMasterKey(masterkey)
diff --git a/tests/fsck/fsck_test.go b/tests/fsck/fsck_test.go
index 2faed97..8e73cf7 100644
--- a/tests/fsck/fsck_test.go
+++ b/tests/fsck/fsck_test.go
@@ -69,6 +69,7 @@ func TestExampleFses(t *testing.T) {
 		fsNames = append(fsNames, e.Name())
 	}
 	for _, n := range fsNames {
+		t.Logf("Checking %q", n)
 		path := "../example_filesystems/" + n
 		cmd := exec.Command(test_helpers.GocryptfsBinary, "-fsck", "-extpass", "echo test", path)
 		outBin, err := cmd.CombinedOutput()