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// Package nametransform encrypts and decrypts filenames.
package nametransform
import (
"bytes"
"crypto/aes"
"encoding/base64"
"syscall"
"github.com/rfjakob/eme"
"github.com/rfjakob/gocryptfs/internal/nametransform/dirivcache"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
// NameTransform is used to transform filenames.
type NameTransform struct {
emeCipher *eme.EMECipher
longNames bool
DirIVCache dirivcache.DirIVCache
// B64 = either base64.URLEncoding or base64.RawURLEncoding, depending
// on the Raw64 feature flag
B64 *base64.Encoding
}
// New returns a new NameTransform instance.
func New(e *eme.EMECipher, longNames bool, raw64 bool) *NameTransform {
b64 := base64.URLEncoding
if raw64 {
b64 = base64.RawURLEncoding
}
return &NameTransform{
emeCipher: e,
longNames: longNames,
B64: b64,
}
}
// 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 {
tlog.Warn.Printf("DecryptName: empty input")
return "", syscall.EBADMSG
}
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.EBADMSG
}
bin = n.emeCipher.Decrypt(iv, bin)
bin, err = unPad16(bin)
if err != nil {
tlog.Debug.Printf("DecryptName: unPad16 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.EBADMSG
}
// A name can never contain a null byte or "/". Make sure we never return those
// to the kernel, even when we read a corrupted (or fuzzed) filesystem.
if bytes.Contains(bin, []byte{0}) || bytes.Contains(bin, []byte("/")) {
return "", syscall.EBADMSG
}
// The name should never be "." or "..".
if bytes.Equal(bin, []byte(".")) || bytes.Equal(bin, []byte("..")) {
return "", syscall.EBADMSG
}
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 = n.emeCipher.Encrypt(iv, bin)
cipherName64 = n.B64.EncodeToString(bin)
return cipherName64
}
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