package cryptfs // Filename encryption / decryption function import ( "crypto/aes" "crypto/cipher" "encoding/base64" "errors" "fmt" "strings" ) const ( OpEncrypt = iota OpDecrypt ) // DecryptName - decrypt base64-encoded encrypted filename "cipherName" func (be *CryptFS) DecryptName(cipherName string, iv []byte) (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)) } 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 - encrypt filename func (be *CryptFS) encryptName(plainName string, iv []byte) 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) cbc := cipher.NewCBCEncrypter(be.blockCipher, iv) cbc.CryptBlocks(bin, bin) cipherName64 := base64.URLEncoding.EncodeToString(bin) return cipherName64 } // TranslatePathZeroIV - encrypt or decrypt path using CBC with a constant all-zero IV. // Just splits the string on "/" and hands the parts to encryptName() / decryptName() func (be *CryptFS) TranslatePathZeroIV(path string, op int) (string, error) { var err error // Empty string means root directory if path == "" { return path, err } zeroIV := make([]byte, DIRIV_LEN) // Run operation on each path component var translatedParts []string parts := strings.Split(path, "/") for _, part := range parts { if part == "" { // This happens on "/foo/bar/" on the front and on the end. // Don't panic. translatedParts = append(translatedParts, "") continue } var newPart string if op == OpEncrypt { newPart = be.encryptName(part, zeroIV) } else { newPart, err = be.DecryptName(part, zeroIV) if err != nil { return "", err } } translatedParts = append(translatedParts, newPart) } return strings.Join(translatedParts, "/"), err } // pad16 - pad filename to 16 byte blocks using standard PKCS#7 padding // https://tools.ietf.org/html/rfc5652#section-6.3 func (be *CryptFS) pad16(orig []byte) (padded []byte) { oldLen := len(orig) if oldLen == 0 { panic("Padding zero-length string makes no sense") } padLen := aes.BlockSize - oldLen%aes.BlockSize if padLen == 0 { padLen = aes.BlockSize } newLen := oldLen + padLen padded = make([]byte, newLen) copy(padded, orig) padByte := byte(padLen) for i := oldLen; i < newLen; i++ { padded[i] = padByte } return padded } // unPad16 - remove padding func (be *CryptFS) unPad16(orig []byte) ([]byte, error) { oldLen := len(orig) if oldLen%aes.BlockSize != 0 { return nil, errors.New("Unaligned size") } // The last byte is always a padding byte padByte := orig[oldLen-1] // The padding byte's value is the padding length padLen := int(padByte) // Padding must be at least 1 byte if padLen <= 0 { return nil, errors.New("Padding cannot be zero-length") } // Larger paddings make no sense if padLen > aes.BlockSize { return nil, errors.New("Padding cannot be larger than 16") } // All padding bytes must be identical for i := oldLen - padLen; i < oldLen; i++ { if orig[i] != padByte { return nil, errors.New(fmt.Sprintf("Padding byte at i=%d is invalid", i)) } } newLen := oldLen - padLen // Padding an empty string makes no sense if newLen == 0 { return nil, errors.New("Unpadded length is zero") } return orig[0:newLen], nil }