Move away from sha1 (#2)

Use sha256 instead of sha1 for calculating the filename hash used to
derive the nonce. This is only applied to new files so that old files
can still be read.

Author: rthellend

storage.go

@@ -30,6 +30,7 @@ import (
 	"compress/gzip"
 	"crypto/rand"
 	"crypto/sha1"
+	"crypto/sha256"
 	"encoding"
 	"encoding/binary"
 	"encoding/gob"
@@ -62,6 +63,7 @@ const (
 	optEncrypted  = 0x10
 	optCompressed = 0x20
 	optPadded     = 0x40
+	optSHA256     = 0x80
 )
 
 var (
@@ -342,7 +344,11 @@ func (s *Storage) OpenManyForUpdate(files []string, objects interface{}) (func(c
 	}, nil
 }
 
-func context(s string) []byte {
+func context(s string, useSHA2 bool) []byte {
+	if useSHA2 {
+		h := sha256.Sum256([]byte(s))
+		return h[:]
+	}
 	h := sha1.Sum([]byte(s))
 	return h[:]
 }
@@ -363,6 +369,7 @@ func (s *Storage) ReadDataFile(filename string, obj interface{}) error {
 		return errors.New("wrong file type")
 	}
 	flags := hdr[4]
+	useSHA2 := flags&optSHA256 != 0
 	if flags&optEncrypted != 0 && s.masterKey == nil {
 		return errors.New("file is encrypted, but a master key was not provided")
 	}
@@ -376,7 +383,7 @@ func (s *Storage) ReadDataFile(filename string, obj interface{}) error {
 		}
 		defer k.Wipe()
 		// Use the file key to decrypt the rest of the file.
-		if r, err = k.StartReader(context(filename), f); err != nil {
+		if r, err = k.StartReader(context(filename, useSHA2), f); err != nil {
 			return err
 		}
 		// Read the header again.
@@ -463,7 +470,7 @@ func (s *Storage) ReadDataFile(filename string, obj interface{}) error {
 // SaveDataFile atomically replace an object in a file.
 func (s *Storage) SaveDataFile(filename string, obj interface{}) error {
 	t := fmt.Sprintf("%s.tmp-%d", filename, time.Now().UnixNano())
-	if err := s.writeFile(context(filename), t, obj); err != nil {
+	if err := s.writeFile(context(filename, true), t, obj); err != nil {
 		return err
 	}
 	// Atomically replace the file.
@@ -472,7 +479,7 @@ func (s *Storage) SaveDataFile(filename string, obj interface{}) error {
 
 // CreateEmptyFile creates an empty file.
 func (s *Storage) CreateEmptyFile(filename string, empty interface{}) error {
-	return s.writeFile(context(filename), filename, empty)
+	return s.writeFile(context(filename, true), filename, empty)
 }
 
 // writeFile writes obj to a file.
@@ -482,15 +489,15 @@ func (s *Storage) writeFile(ctx []byte, filename string, obj interface{}) (retEr
 		return err
 	}
 
-	var flags byte
+	flags := byte(optSHA256)
 	if _, ok := obj.(encoding.BinaryMarshaler); ok {
-		flags = optBinaryEncoded
+		flags |= optBinaryEncoded
 	} else if _, ok := obj.(*[]byte); ok {
-		flags = optRawBytes
+		flags |= optRawBytes
 	} else if s.useGOB {
-		flags = optGOBEncoded
+		flags |= optGOBEncoded
 	} else {
-		flags = optJSONEncoded
+		flags |= optJSONEncoded
 	}
 	if s.masterKey != nil {
 		flags |= optEncrypted
@@ -563,12 +570,12 @@ func (s *Storage) OpenBlobWrite(writeFileName, finalFileName string) (io.WriteCl
 	if err := createParentIfNotExist(fn); err != nil {
 		return nil, err
 	}
-	var flags byte = optRawBytes
+	var flags byte = optRawBytes | optSHA256
 	if s.masterKey != nil {
 		flags |= optEncrypted
 		flags |= optPadded
 	}
-	return s.openWriteStream(context(finalFileName), fn, flags, 1024*1024)
+	return s.openWriteStream(context(finalFileName, true), fn, flags, 1024*1024)
 }
 
 // OpenBlobRead opens a blob file for reading.
@@ -591,6 +598,7 @@ func (s *Storage) OpenBlobRead(filename string) (stream io.ReadSeekCloser, retEr
 		return nil, errors.New("wrong file type")
 	}
 	flags := hdr[4]
+	useSHA2 := flags&optSHA256 != 0
 	if flags&optRawBytes == 0 {
 		return nil, errors.New("blob files is not raw bytes")
 	}
@@ -610,7 +618,7 @@ func (s *Storage) OpenBlobRead(filename string) (stream io.ReadSeekCloser, retEr
 		}
 		defer k.Wipe()
 		// Use the file key to decrypt the rest of the file.
-		if r, err = k.StartReader(context(filename), f); err != nil {
+		if r, err = k.StartReader(context(filename, useSHA2), f); err != nil {
 			return nil, err
 		}
 		// Read the header again.

storage_test.go

@@ -403,7 +403,7 @@ func RunBenchmarkOpenForUpdate(b *testing.B, kb int, k crypto.EncryptionKey, com
 		}
 		obj.M[string(key)] = string(value)
 	}
-	if err := s.writeFile(context("testfile"), "testfile", &obj); err != nil {
+	if err := s.writeFile(context("testfile", true), "testfile", &obj); err != nil {
 		b.Fatalf("s.writeFile: %v", err)
 	}
 	fi, err := os.Stat(file)