3 files changed, 20 insertions, 7 deletions
diff --git a/internal/stupidgcm/stupidgcm.go b/internal/stupidgcm/stupidgcm.go
index a1a5a14..133ee1a 100644
--- a/internal/stupidgcm/stupidgcm.go
+++ b/internal/stupidgcm/stupidgcm.go
@@ -26,17 +26,21 @@ const (
 
 // stupidGCM implements the cipher.AEAD interface
 type stupidGCM struct {
-	key []byte
+	key         []byte
+	forceDecode bool
 }
 
+//authentication error
+var AuthError error = fmt.Errorf("stupidgcm: message authentication failed")
+
 var _ cipher.AEAD = &stupidGCM{}
 
 // New returns a new cipher.AEAD implementation..
-func New(key []byte) cipher.AEAD {
+func New(key []byte, forceDecode bool) cipher.AEAD {
 	if len(key) != keyLen {
 		log.Panicf("Only %d-byte keys are supported", keyLen)
 	}
-	return stupidGCM{key: key}
+	return stupidGCM{key: key, forceDecode: forceDecode}
 }
 
 func (g stupidGCM) NonceSize() int {
@@ -186,7 +190,13 @@ func (g stupidGCM) Open(dst, iv, in, authData []byte) ([]byte, error) {
 	C.EVP_CIPHER_CTX_free(ctx)
 
 	if res != 1 {
-		return nil, fmt.Errorf("stupidgcm: message authentication failed")
+		// The error code must always be checked by the calling function, because the decrypted buffer
+		// may contain corrupted data that we are returning in case the user forced reads
+		if g.forceDecode == true {
+			return append(dst, buf...), AuthError
+		} else {
+			return nil, AuthError
+		}
 	}
 
 	return append(dst, buf...), nil
diff --git a/internal/stupidgcm/stupidgcm_test.go b/internal/stupidgcm/stupidgcm_test.go
index 3081085..eb322f2 100644
--- a/internal/stupidgcm/stupidgcm_test.go
+++ b/internal/stupidgcm/stupidgcm_test.go
@@ -27,7 +27,7 @@ func randBytes(n int) []byte {
 // GCM implemenatation and verifies that the results are identical.
 func TestEncryptDecrypt(t *testing.T) {
 	key := randBytes(32)
-	sGCM := New(key)
+	sGCM := New(key, false)
 	authData := randBytes(24)
 	iv := randBytes(16)
 	dst := make([]byte, 71) // 71 = random length
@@ -77,7 +77,7 @@ func TestEncryptDecrypt(t *testing.T) {
 // error
 func TestCorruption(t *testing.T) {
 	key := randBytes(32)
-	sGCM := New(key)
+	sGCM := New(key, false)
 	authData := randBytes(24)
 	iv := randBytes(16)
 
diff --git a/internal/stupidgcm/without_openssl.go b/internal/stupidgcm/without_openssl.go
index 18c5ddc..52d8fa0 100644
--- a/internal/stupidgcm/without_openssl.go
+++ b/internal/stupidgcm/without_openssl.go
@@ -14,12 +14,15 @@ const (
 	BuiltWithoutOpenssl = true
 )
 
+//authentication error - needed to compile as same varaible is exported when openssl is enable via stupidgcm.go
+var AuthError error = fmt.Errorf("stupidgcm: message authentication failed with openssl disabled!")
+
 func errExit() {
 	fmt.Fprintln(os.Stderr, "gocryptfs has been compiled without openssl support but you are still trying to use openssl")
 	os.Exit(2)
 }
 
-func New(_ []byte) stupidGCM {
+func New(_ []byte, _ bool) stupidGCM {
 	errExit()
 	// Never reached
 	return stupidGCM{}