cryptocore: add support for GCM-SIV

4 files changed, 40 insertions, 29 deletions

diff --git a/internal/cryptocore/cryptocore.go b/internal/cryptocore/cryptocore.go
index 1839aa2..a6708bd 100644
--- a/internal/cryptocore/cryptocore.go
+++ b/internal/cryptocore/cryptocore.go
@@ -8,17 +8,29 @@ import (
 	"fmt"
 
 	"github.com/rfjakob/gocryptfs/internal/stupidgcm"
+
+	"github.com/rfjakob/gcmsiv"
 )
 
+type BackendTypeEnum int
+
 const (
 	KeyLen     = 32 // AES-256
 	AuthTagLen = 16
+
+	_                              = iota // Skip zero
+	BackendOpenSSL BackendTypeEnum = iota
+	BackendGoGCM   BackendTypeEnum = iota
+	BackendGCMSIV  BackendTypeEnum = iota
 )
 
 type CryptoCore struct {
+	// AES-256 block cipher. This is used for EME filename encryption.
 	BlockCipher cipher.Block
-	Gcm         cipher.AEAD
-	GcmIVGen    *nonceGenerator
+	// GCM or GCM-SIV. This is used for content encryption.
+	AEADCipher cipher.AEAD
+	// GCM needs unique IVs (nonces)
+	IVGenerator *nonceGenerator
 	IVLen       int
 }
 
@@ -27,17 +39,12 @@ type CryptoCore struct {
 // Even though the "GCMIV128" feature flag is now mandatory, we must still
 // support 96-bit IVs here because they are used for encrypting the master
 // key in gocryptfs.conf.
-func New(key []byte, useOpenssl bool, GCMIV128 bool) *CryptoCore {
-
+func New(key []byte, backend BackendTypeEnum, IVBitLen int) *CryptoCore {
 	if len(key) != KeyLen {
 		panic(fmt.Sprintf("Unsupported key length %d", len(key)))
 	}
-
 	// We want the IV size in bytes
-	IVLen := 96 / 8
-	if GCMIV128 {
-		IVLen = 128 / 8
-	}
+	IVLen := IVBitLen / 8
 
 	// Name encryption always uses built-in Go AES through BlockCipher.
 	// Content encryption uses BlockCipher only if useOpenssl=false.
@@ -47,20 +54,27 @@ func New(key []byte, useOpenssl bool, GCMIV128 bool) *CryptoCore {
 	}
 
 	var gcm cipher.AEAD
-	if useOpenssl && GCMIV128 {
-		// stupidgcm only supports 128-bit IVs
+	switch backend {
+	case BackendOpenSSL:
+		if IVLen != 16 {
+			panic("stupidgcm only supports 128-bit IVs")
+		}
 		gcm = stupidgcm.New(key)
-	} else {
+	case BackendGoGCM:
 		gcm, err = goGCMWrapper(blockCipher, IVLen)
-		if err != nil {
-			panic(err)
-		}
+	case BackendGCMSIV:
+		gcm, err = gcmsiv.NewGCMSIV(key)
+	default:
+		panic("unknown backend cipher")
+	}
+	if err != nil {
+		panic(err)
 	}
 
 	return &CryptoCore{
 		BlockCipher: blockCipher,
-		Gcm:         gcm,
-		GcmIVGen:    &nonceGenerator{nonceLen: IVLen},
+		AEADCipher:  gcm,
+		IVGenerator: &nonceGenerator{nonceLen: IVLen},
 		IVLen:       IVLen,
 	}
 }
diff --git a/internal/cryptocore/cryptocore_go1.4_test.go b/internal/cryptocore/cryptocore_go1.4_test.go
index 3460d02..14e1e03 100644
--- a/internal/cryptocore/cryptocore_go1.4_test.go
+++ b/internal/cryptocore/cryptocore_go1.4_test.go
@@ -7,7 +7,8 @@ import (
 	"testing"
 )
 
-// Native Go crypto with 128-bit IVs is only supported on Go 1.5 and up
+// Native Go crypto with 128-bit IVs is only supported on Go 1.5 and up,
+// this should panic.
 func TestCryptoCoreNewGo14(t *testing.T) {
 	defer func() {
 		if r := recover(); r == nil {
@@ -15,5 +16,5 @@ func TestCryptoCoreNewGo14(t *testing.T) {
 		}
 	}()
 	key := make([]byte, 32)
-	New(key, false, true)
+	New(key, BackendGoGCM, 128)
 }
diff --git a/internal/cryptocore/cryptocore_go1.5_test.go b/internal/cryptocore/cryptocore_go1.5_test.go
index 1c93254..f9d38e9 100644
--- a/internal/cryptocore/cryptocore_go1.5_test.go
+++ b/internal/cryptocore/cryptocore_go1.5_test.go
@@ -9,7 +9,7 @@ import (
 
 func TestCryptoCoreNewGo15(t *testing.T) {
 	key := make([]byte, 32)
-	c := New(key, false, true)
+	c := New(key, BackendGoGCM, 128)
 	if c.IVLen != 16 {
 		t.Fail()
 	}
diff --git a/internal/cryptocore/cryptocore_test.go b/internal/cryptocore/cryptocore_test.go
index 1151591..9da6059 100644
--- a/internal/cryptocore/cryptocore_test.go
+++ b/internal/cryptocore/cryptocore_test.go
@@ -4,23 +4,19 @@ import (
 	"testing"
 )
 
-// "New" should accept all param combinations
+// "New" should accept at least these param combinations
 func TestCryptoCoreNew(t *testing.T) {
 	key := make([]byte, 32)
 
-	c := New(key, true, true)
+	c := New(key, BackendOpenSSL, 128)
 	if c.IVLen != 16 {
 		t.Fail()
 	}
-	c = New(key, true, false)
+	c = New(key, BackendGoGCM, 96)
 	if c.IVLen != 12 {
 		t.Fail()
 	}
-	c = New(key, false, false)
-	if c.IVLen != 12 {
-		t.Fail()
-	}
-	// "New(key, false, true)" is tested for Go 1.4 and 1.5+ seperately
+	// "New(key, BackendGoGCM, 128)" is tested for Go 1.4 and 1.5+ seperately
 }
 
 // "New" should panic on any key not 32 bytes long
@@ -32,5 +28,5 @@ func TestNewPanic(t *testing.T) {
 	}()
 
 	key := make([]byte, 16)
-	New(key, true, true)
+	New(key, BackendOpenSSL, 128)
 }