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// Package nametransform encrypts and decrypts filenames.
package nametransform
import (
"crypto/aes"
"encoding/base64"
"syscall"
"github.com/rfjakob/eme"
"github.com/rfjakob/gocryptfs/internal/cryptocore"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
// NameTransform is used to transform filenames.
type NameTransform struct {
cryptoCore *cryptocore.CryptoCore
longNames bool
DirIVCache dirIVCache
// b64 = either base64.URLEncoding or base64.RawURLEncoding
b64 *base64.Encoding
}
// New returns a new NameTransform instance.
func New(c *cryptocore.CryptoCore, longNames bool, raw64 bool) *NameTransform {
b64 := base64.URLEncoding
if raw64 {
b64 = base64.RawURLEncoding
}
return &NameTransform{
cryptoCore: c,
longNames: longNames,
b64: b64,
}
}
// 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
}
// 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
}
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