reverse: implement dynamic diriv

Introduce a unique per-directory diriv that is generated
by hashing the encrypted directory path.

1 files changed, 42 insertions, 0 deletions

diff --git a/internal/fusefrontend_reverse/diriv.go b/internal/fusefrontend_reverse/diriv.go
new file mode 100644
index 0000000..c4a93e4
--- /dev/null
+++ b/internal/fusefrontend_reverse/diriv.go
@@ -0,0 +1,42 @@
+package fusefrontend_reverse
+
+import (
+	"crypto/sha256"
+
+	"github.com/hanwen/go-fuse/fuse"
+	"github.com/hanwen/go-fuse/fuse/nodefs"
+
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+)
+
+// deriveDirIV derives the DirIV from the directory path by simply hashing it
+func deriveDirIV(dirPath string) []byte {
+	hash := sha256.Sum256([]byte(dirPath))
+	return hash[:nametransform.DirIVLen]
+}
+
+type dirIVFile struct {
+	// Embed nodefs.defaultFile for a ENOSYS implementation of all methods
+	nodefs.File
+	// file content
+	content []byte
+}
+
+func NewDirIVFile(dirPath string) (nodefs.File, fuse.Status) {
+	return &dirIVFile{
+		File:    nodefs.NewDefaultFile(),
+		content: deriveDirIV(dirPath),
+	}, fuse.OK
+}
+
+// Read - FUSE call
+func (f *dirIVFile) Read(buf []byte, off int64) (resultData fuse.ReadResult, status fuse.Status) {
+	if off >= int64(len(f.content)) {
+		return nil, fuse.OK
+	}
+	end := int(off) + len(buf)
+	if end > len(f.content) {
+		end = len(f.content)
+	}
+	return fuse.ReadResultData(f.content[off:end]), fuse.OK
+}