Use "-openssl=auto" by default

Go GCM is faster than OpenSSL if the CPU has AES instructions
and you are running Go 1.6+.

See #23 for details.

Documentation/MANPAGE.md

@@ -96,8 +96,10 @@ continue be printed to stdout and stderr.
 used internally for daemonization.
 
 **-openssl bool**
-:	Use OpenSSL instead of built-in Go crypto (default true). Using
-built-in crypto is 4x slower.
+:	Use OpenSSL instead of built-in Go crypto (default "auto"). Using
+built-in crypto is 4x slower unless you CPU has AES instructions and
+you are using Go 1.6+. In mode "auto", gocrypts chooses the faster
+option.
 
 **-passwd**
 :	Change password

internal/stupidgcm/prefer_go1.5.go

@@ -0,0 +1,9 @@
+// +build !go1.6
+// = go 1.5 or lower
+
+package stupidgcm
+
+func PreferOpenSSL() bool {
+	// OpenSSL is always faster than Go GCM on old Go versions.
+	return true
+}

internal/stupidgcm/prefer_go1.6.go

@@ -0,0 +1,31 @@
+// +build go1.6
+// = go 1.6 or higher
+
+package stupidgcm
+
+import (
+	"fmt"
+	"io/ioutil"
+	"regexp"
+	"runtime"
+)
+
+// PreferOpenSSL tells us if OpenSSL is faster than Go GCM on this machine.
+// Go GCM is fastern when the CPU has AES instructions and Go is v1.6 or higher.
+//
+// See https://github.com/rfjakob/gocryptfs/issues/23#issuecomment-218286502
+// for benchmarks.
+func PreferOpenSSL() bool {
+	runtime.G
+	ci, err := ioutil.ReadFile("/proc/cpuinfo")
+	if err != nil {
+		fmt.Println(err)
+		return true
+	}
+	match, err := regexp.Match("(?m)^flags.*\baes\b", ci)
+	if err != nil {
+		fmt.Println(err)
+		return true
+	}
+	return match
+}

internal/stupidgcm/stupidgcm_test.go

@@ -13,6 +13,7 @@ import (
 	"crypto/cipher"
 	"crypto/rand"
 	"encoding/hex"
+	"fmt"
 	"testing"
 )
 
@@ -26,6 +27,15 @@ func randBytes(n int) []byte {
 	return b
 }
 
+func TestPreferOpenSSL(t *testing.T) {
+	h := PreferOpenSSL()
+	p := "Go GCM"
+	if h {
+		p = "OpenSSL"
+	}
+	fmt.Printf("PreferOpenSSL=%v, gocryptfs will prefer %s\n", h, p)
+}
+
 // TestEncryptDecrypt encrypts and decrypts using both stupidgcm and Go's built-in
 // GCM implemenatation and verifies that the results are identical.
 func TestEncryptDecrypt(t *testing.T) {

main.go

@@ -11,6 +11,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"runtime/pprof"
+	"strconv"
 	"syscall"
 	"time"
 
@@ -25,6 +26,7 @@ import (
 	"github.com/rfjakob/gocryptfs/internal/cryptocore"
 	"github.com/rfjakob/gocryptfs/internal/fusefrontend"
 	"github.com/rfjakob/gocryptfs/internal/nametransform"
+	"github.com/rfjakob/gocryptfs/internal/stupidgcm"
 	"github.com/rfjakob/gocryptfs/internal/toggledlog"
 )
 
@@ -149,14 +151,15 @@ func main() {
 	setupColors()
 
 	// Parse command line arguments
+	var opensslAuto string
 	flagSet = flag.NewFlagSet(toggledlog.ProgramName, flag.ExitOnError)
 	flagSet.Usage = usageText
 	flagSet.BoolVar(&args.debug, "d", false, "")
 	flagSet.BoolVar(&args.debug, "debug", false, "Enable debug output")
 	flagSet.BoolVar(&args.fusedebug, "fusedebug", false, "Enable fuse library debug output")
 	flagSet.BoolVar(&args.init, "init", false, "Initialize encrypted directory")
 	flagSet.BoolVar(&args.zerokey, "zerokey", false, "Use all-zero dummy master key")
-	flagSet.BoolVar(&args.openssl, "openssl", true, "Use OpenSSL instead of built-in Go crypto")
+	flagSet.StringVar(&opensslAuto, "openssl", "auto", "Use OpenSSL instead of built-in Go crypto")
 	flagSet.BoolVar(&args.passwd, "passwd", false, "Change password")
 	flagSet.BoolVar(&args.foreground, "f", false, "Stay in the foreground")
 	flagSet.BoolVar(&args.version, "version", false, "Print version and exit")
@@ -180,6 +183,17 @@ func main() {
 		"Setting this to a lower value speeds up mounting but makes the password susceptible to brute-force attacks")
 	flagSet.Parse(os.Args[1:])
 
+	// "-openssl" needs some post-processing
+	if opensslAuto == "auto" {
+		args.openssl = stupidgcm.PreferOpenSSL()
+	} else {
+		args.openssl, err = strconv.ParseBool(opensslAuto)
+		if err != nil {
+			fmt.Printf(colorRed+"Invalid \"-openssl\" setting: %v\n"+colorReset, err)
+			os.Exit(ERREXIT_USAGE)
+		}
+	}
+
 	// Fork a child into the background if "-f" is not set AND we are mounting a filesystem
 	if !args.foreground && flagSet.NArg() == 2 {
 		forkChild() // does not return
@@ -255,7 +269,7 @@ func main() {
 	}
 	// "-openssl"
 	if args.openssl == false {
-		toggledlog.Info.Printf("Openssl disabled")
+		toggledlog.Info.Printf("OpenSSL disabled, using Go GCM")
 	}
 	// Operation flags: init, passwd or mount
 	// "-init"