// decryptSegment decrypts a path segment
func (c *cipher) decryptSegment(ciphertext string) (string, error) {
if ciphertext == "" {
return "", nil
}
rawCiphertext, err := decodeFileName(ciphertext)
if err != nil {
return "", err
}
if len(rawCiphertext)%nameCipherBlockSize != 0 {
return "", ErrorNotAMultipleOfBlocksize
}
if len(rawCiphertext) == 0 {
// not possible if decodeFilename() working correctly
return "", ErrorTooShortAfterDecode
}
paddedPlaintext := eme.Transform(c.block, c.nameTweak[:], rawCiphertext, eme.DirectionDecrypt)
plaintext, err := pkcs7.Unpad(nameCipherBlockSize, paddedPlaintext)
if err != nil {
return "", err
}
err = checkValidString(plaintext)
if err != nil {
return "", err
}
return string(plaintext), err
}
// decryptName - decrypt base64-encoded encrypted filename "cipherName".
// The used encryption is either CBC or EME, depending on the "EMENames" argument.
func (be *CryptFS) decryptName(cipherName string, iv []byte, EMENames bool) (string, error) {
// Make sure relative symlinks still work after encryption
// by passing these through unchanged
if cipherName == "." || cipherName == ".." {
return cipherName, nil
}
bin, err := base64.URLEncoding.DecodeString(cipherName)
if err != nil {
return "", err
}
if len(bin)%aes.BlockSize != 0 {
return "", fmt.Errorf("Decoded length %d is not a multiple of the AES block size", len(bin))
}
if EMENames {
bin = eme.Transform(be.blockCipher, iv, bin, eme.DirectionDecrypt)
} else {
cbc := cipher.NewCBCDecrypter(be.blockCipher, iv)
cbc.CryptBlocks(bin, bin)
}
bin, err = be.unPad16(bin)
if err != nil {
return "", err
}
plain := string(bin)
return plain, err
}
// EncryptName encrypts "plainName", returns a base64-encoded "cipherName64".
// Used internally by EncryptPathDirIV().
// The encryption is either CBC or EME, depending on "useEME".
//
// This function is exported because fusefrontend needs access to the full (not hashed)
// name if longname is used. Otherwise you should use EncryptPathDirIV()
func (n *NameTransform) EncryptName(plainName string, iv []byte) (cipherName64 string) {
bin := []byte(plainName)
bin = pad16(bin)
bin = eme.Transform(n.cryptoCore.BlockCipher, iv, bin, eme.DirectionEncrypt)
cipherName64 = n.b64.EncodeToString(bin)
return cipherName64
}
// encryptSegment encrypts a path segment
//
// This uses EME with AES
//
// EME (ECB-Mix-ECB) is a wide-block encryption mode presented in the
// 2003 paper "A Parallelizable Enciphering Mode" by Halevi and
// Rogaway.
//
// This makes for determinstic encryption which is what we want - the
// same filename must encrypt to the same thing.
//
// This means that
// * filenames with the same name will encrypt the same
// * filenames which start the same won't have a common prefix
func (c *cipher) encryptSegment(plaintext string) string {
if plaintext == "" {
return ""
}
paddedPlaintext := pkcs7.Pad(nameCipherBlockSize, []byte(plaintext))
ciphertext := eme.Transform(c.block, c.nameTweak[:], paddedPlaintext, eme.DirectionEncrypt)
return encodeFileName(ciphertext)
}
// encryptName - encrypt "plainName", return base64-encoded "cipherName64"
// The used encryption is either CBC or EME, depending on the "EMENames" argument.
func (be *CryptFS) encryptName(plainName string, iv []byte, EMENames bool) (cipherName64 string) {
// Make sure relative symlinks still work after encryption
// by passing these trough unchanged
if plainName == "." || plainName == ".." {
return plainName
}
bin := []byte(plainName)
bin = be.pad16(bin)
if EMENames {
bin = eme.Transform(be.blockCipher, iv, bin, eme.DirectionEncrypt)
} else {
cbc := cipher.NewCBCEncrypter(be.blockCipher, iv)
cbc.CryptBlocks(bin, bin)
}
cipherName64 = base64.URLEncoding.EncodeToString(bin)
return cipherName64
}
// DecryptName - decrypt base64-encoded encrypted filename "cipherName"
//
// This function is exported because it allows for a very efficient readdir
// implementation (read IV once, decrypt all names using this function).
func (n *NameTransform) DecryptName(cipherName string, iv []byte) (string, error) {
bin, err := n.b64.DecodeString(cipherName)
if err != nil {
return "", err
}
if len(bin)%aes.BlockSize != 0 {
tlog.Debug.Printf("DecryptName %q: decoded length %d is not a multiple of 16", cipherName, len(bin))
return "", syscall.EINVAL
}
bin = eme.Transform(n.cryptoCore.BlockCipher, iv, bin, eme.DirectionDecrypt)
bin, err = unPad16(bin)
if err != nil {
tlog.Debug.Printf("pad16 error detail: %v", err)
// unPad16 returns detailed errors including the position of the
// incorrect bytes. Kill the padding oracle by lumping everything into
// a generic error.
return "", syscall.EINVAL
}
plain := string(bin)
return plain, err
}
