Re-design of the original gocryptfs code to work as a library.
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libgocryptfs/internal/nametransform/names.go

131 lines
3.6 KiB

// Package nametransform encrypts and decrypts filenames.
package nametransform
import (
"crypto/aes"
"encoding/base64"
"path/filepath"
"syscall"
"github.com/rfjakob/eme"
)
const (
// Like ext4, we allow at most 255 bytes for a file name.
NameMax = 255
)
// NameTransform is used to transform filenames.
type NameTransform struct {
emeCipher *eme.EMECipher
longNames bool
// B64 = either base64.URLEncoding or base64.RawURLEncoding, depending
// on the Raw64 feature flag
B64 *base64.Encoding
// Patterns to bypass decryption
badnamePatterns []string
deterministicNames bool
}
// New returns a new NameTransform instance.
func New(e *eme.EMECipher, longNames bool, raw64 bool, badname []string, deterministicNames bool) *NameTransform {
b64 := base64.URLEncoding
if raw64 {
b64 = base64.RawURLEncoding
}
return &NameTransform{
emeCipher: e,
longNames: longNames,
B64: b64,
badnamePatterns: badname,
deterministicNames: deterministicNames,
}
}
// DecryptName calls decryptName to try and decrypt a base64-encoded encrypted
// filename "cipherName", and failing that checks if it can be bypassed
func (n *NameTransform) DecryptName(cipherName string, iv []byte) (string, error) {
res, err := n.decryptName(cipherName, iv)
if err != nil && n.HaveBadnamePatterns() {
return n.decryptBadname(cipherName, iv)
}
return res, err
}
// decryptName decrypts a base64-encoded encrypted filename "cipherName" using the
// initialization vector "iv".
func (n *NameTransform) decryptName(cipherName string, iv []byte) (string, error) {
bin, err := n.B64.DecodeString(cipherName)
if err != nil {
return "", err
}
if len(bin) == 0 {
return "", syscall.EBADMSG
}
if len(bin)%aes.BlockSize != 0 {
return "", syscall.EBADMSG
}
bin = n.emeCipher.Decrypt(iv, bin)
bin, err = unPad16(bin)
if err != nil {
return "", syscall.EBADMSG
}
plain := string(bin)
if err := IsValidName(plain); err != nil {
return "", syscall.EBADMSG
}
return plain, err
}
// EncryptName encrypts "plainName", returns a base64-encoded "cipherName64",
// encrypted using EME (https://github.com/rfjakob/eme).
//
// This function is exported because in some cases, fusefrontend needs access
// to the full (not hashed) name if longname is used.
func (n *NameTransform) EncryptName(plainName string, iv []byte) (cipherName64 string, err error) {
if err := IsValidName(plainName); err != nil {
return "", syscall.EBADMSG
}
bin := []byte(plainName)
bin = pad16(bin)
bin = n.emeCipher.Encrypt(iv, bin)
cipherName64 = n.B64.EncodeToString(bin)
return cipherName64, nil
}
// EncryptAndHashName encrypts "name" and hashes it to a longname if it is
// too long.
// Returns ENAMETOOLONG if "name" is longer than 255 bytes.
func (be *NameTransform) EncryptAndHashName(name string, iv []byte) (string, error) {
// Prevent the user from creating files longer than 255 chars.
if len(name) > NameMax {
return "", syscall.ENAMETOOLONG
}
cName, err := be.EncryptName(name, iv)
if err != nil {
return "", err
}
if be.longNames && len(cName) > NameMax {
return be.HashLongName(cName), nil
}
return cName, nil
}
// B64EncodeToString returns a Base64-encoded string
func (n *NameTransform) B64EncodeToString(src []byte) string {
return n.B64.EncodeToString(src)
}
// B64DecodeString decodes a Base64-encoded string
func (n *NameTransform) B64DecodeString(s string) ([]byte, error) {
return n.B64.DecodeString(s)
}
// Dir is like filepath.Dir but returns "" instead of ".".
func Dir(path string) string {
d := filepath.Dir(path)
if d == "." {
return ""
}
return d
}