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// Package nametransform encrypts and decrypts filenames.
package nametransform
import (
"crypto/aes"
"encoding/base64"
"math"
"path/filepath"
"syscall"
"github.com/rfjakob/eme"
"github.com/rfjakob/gocryptfs/v2/internal/tlog"
)
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
// Names longer than `longNameMax` are hashed. Set to MaxInt when
// longnames are disabled.
longNameMax int
// 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.
//
// If `longNames` is set, names longer than `longNameMax` are hashed to
// `gocryptfs.longname.[sha256]`.
// Pass `longNameMax = 0` to use the default value (255).
func New(e *eme.EMECipher, longNames bool, longNameMax uint8, raw64 bool, badname []string, deterministicNames bool) *NameTransform {
tlog.Debug.Printf("nametransform.New: longNameMax=%v, raw64=%v, badname=%q",
longNameMax, raw64, badname)
b64 := base64.URLEncoding
if raw64 {
b64 = base64.RawURLEncoding
}
var effectiveLongNameMax int = math.MaxInt32
if longNames {
if longNameMax == 0 {
effectiveLongNameMax = NameMax
} else {
effectiveLongNameMax = int(longNameMax)
}
}
return &NameTransform{
emeCipher: e,
longNameMax: effectiveLongNameMax,
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() {
res, err = n.decryptBadname(cipherName, iv)
}
if err != nil {
return "", err
}
if err := IsValidName(res); err != nil {
tlog.Warn.Printf("DecryptName %q: invalid name after decryption: %v", cipherName, err)
return "", syscall.EBADMSG
}
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 {
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.Warn.Printf("decryptName %q: unPad16 error: %v", cipherName, err)
return "", syscall.EBADMSG
}
plain := string(bin)
return plain, err
}
// EncryptName encrypts a file name "plainName" and returns a base64-encoded "cipherName64",
// encrypted using EME (https://github.com/rfjakob/eme).
//
// plainName is checked for null bytes, slashes etc. and such names are rejected
// with an error.
//
// 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 {
tlog.Warn.Printf("EncryptName %q: invalid plainName: %v", plainName, err)
return "", syscall.EBADMSG
}
return n.encryptName(plainName, iv), nil
}
// encryptName encrypts "plainName" and returns a base64-encoded "cipherName64",
// encrypted using EME (https://github.com/rfjakob/eme).
//
// No checks for null bytes etc are performed against plainName.
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
}
// 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 len(cName) > be.longNameMax {
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
}
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