crypt: fix directory names which look like versioned file names

The --b2-versions support added in 3fe2aaf96 strips a version string
from the last segment of a path before encrypting it, so that the
plain text version suffixes which the underlying backend appends to
encrypted file leaf names can be handled. EncryptDirName and
DecryptDirName share that code, so the last segment of a *directory*
name was version stripped too. Only file leaf names are ever given a
version string by the backend - a directory gets a
version-string-like name from the user, and such a name is encrypted
verbatim when it appears as the parent of a file name, so the same
directory ended up with two different encryptions.

Before this change, with a directory whose name matches rclone's
version format, eg dir-v2001-02-03-040506-123:

    rclone copy file.txt crypt:dir-v2001-02-03-040506-123/
    rclone ls crypt:dir-v2001-02-03-040506-123
    # => "directory not found" - the file is invisible to listings
    rclone mkdir crypt:dir-v2001-02-03-040506-123
    # => creates a second directory with the same decrypted name

After this change EncryptDirName and DecryptDirName encrypt directory
names verbatim, so a directory encrypts the same way whether it is
named on its own or as the parent of a file. Version strings are only
added to file names by the underlying backend, so --b2-versions is
unaffected and the existing version tests are untouched.

A directory which was created by the old EncryptDirName will no longer
decrypt and will be reported as undecryptable in listings. Such
directories were already unusable - anything copied into one was
written to a different encrypted directory - so nothing which worked
before is broken by this.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/crypt/cipher.go

@@ -486,7 +486,14 @@ func (c *Cipher) deobfuscateSegment(ciphertext string) (string, error) {
 }
 
 // encryptFileName encrypts a file path
-func (c *Cipher) encryptFileName(in string) string {
+//
+// If stripVersion is set then a version string on the last segment (as
+// used by --b2-versions) is removed before encryption and put back in
+// plain text afterwards. Only file leaf names are given version strings
+// by the underlying backend, so it must not be set for directory names,
+// which would otherwise encrypt differently from the same directory
+// appearing as the parent of a file name.
+func (c *Cipher) encryptFileName(in string, stripVersion bool) string {
 	segments := strings.Split(in, "/")
 	for i := range segments {
 		// Skip directory name encryption if the user chose to
@@ -499,7 +506,7 @@ func (c *Cipher) encryptFileName(in string) string {
 		// of the file name gets encrypted/obfuscated
 		hasVersion := false
 		var t time.Time
-		if i == (len(segments)-1) && version.Match(segments[i]) {
+		if stripVersion && i == (len(segments)-1) && version.Match(segments[i]) {
 			var s string
 			t, s = version.Remove(segments[i])
 			// version.Remove can fail, in which case it returns segments[i]
@@ -529,7 +536,7 @@ func (c *Cipher) EncryptFileName(in string) string {
 	if c.mode == NameEncryptionOff {
 		return in + c.encryptedSuffix
 	}
-	return c.encryptFileName(in)
+	return c.encryptFileName(in, true)
 }
 
 // EncryptDirName encrypts a directory path
@@ -537,11 +544,13 @@ func (c *Cipher) EncryptDirName(in string) string {
 	if c.mode == NameEncryptionOff || !c.dirNameEncrypt {
 		return in
 	}
-	return c.encryptFileName(in)
+	return c.encryptFileName(in, false)
 }
 
 // decryptFileName decrypts a file path
-func (c *Cipher) decryptFileName(in string) (string, error) {
+//
+// stripVersion is as for encryptFileName.
+func (c *Cipher) decryptFileName(in string, stripVersion bool) (string, error) {
 	segments := strings.Split(in, "/")
 	for i := range segments {
 		var err error
@@ -555,7 +564,7 @@ func (c *Cipher) decryptFileName(in string) (string, error) {
 		// of the file name gets decrypted/deobfuscated
 		hasVersion := false
 		var t time.Time
-		if i == (len(segments)-1) && version.Match(segments[i]) {
+		if stripVersion && i == (len(segments)-1) && version.Match(segments[i]) {
 			var s string
 			t, s = version.Remove(segments[i])
 			// version.Remove can fail, in which case it returns segments[i]
@@ -601,7 +610,7 @@ func (c *Cipher) DecryptFileName(in string) (string, error) {
 		// Leave the version string on, if it was there
 		return decrypted, nil
 	}
-	return c.decryptFileName(in)
+	return c.decryptFileName(in, true)
 }
 
 // DecryptDirName decrypts a directory path
@@ -609,7 +618,7 @@ func (c *Cipher) DecryptDirName(in string) (string, error) {
 	if c.mode == NameEncryptionOff || !c.dirNameEncrypt {
 		return in, nil
 	}
-	return c.decryptFileName(in)
+	return c.decryptFileName(in, false)
 }
 
 // NameEncryptionMode returns the encryption mode in use for names

backend/crypt/cipher_test.go

@@ -682,6 +682,28 @@ func TestNonStandardDecryptDirName(t *testing.T) {
 	}
 }
 
+// Test directories whose name looks like it has a version string -
+// these encrypt verbatim, so that EncryptDirName agrees with the same
+// directory encrypted as the parent of a file name
+func TestVersionedDirName(t *testing.T) {
+	const dir = "dir-v2001-02-03-040506-123"
+	for _, encoding := range []string{"base32", "base64", "base32768"} {
+		enc, _ := NewNameEncoding(encoding)
+		for _, mode := range []NameEncryptionMode{NameEncryptionStandard, NameEncryptionObfuscated} {
+			c, _ := newCipher(mode, "", "", true, enc)
+			what := fmt.Sprintf("Testing %q (mode=%v)", encoding, mode)
+			// Check EncryptDirName matches the parent of an encrypted file name
+			encryptedDir := c.EncryptDirName(dir)
+			encryptedFile := c.EncryptFileName(dir + "/file.txt")
+			assert.Equal(t, encryptedDir+"/", encryptedFile[:strings.LastIndex(encryptedFile, "/")+1], what)
+			// Check the encrypted directory name round trips OK
+			decryptedDir, err := c.DecryptDirName(encryptedDir)
+			assert.NoError(t, err, what)
+			assert.Equal(t, dir, decryptedDir, what)
+		}
+	}
+}
+
 func TestEncryptedSize(t *testing.T) {
 	c, _ := newCipher(NameEncryptionStandard, "", "", true, nil)
 	for _, test := range []struct {