2abfae283c
This happened when the underlying reader returned io.ErrUnexpectedEOF. The error handling for the call to io.ReadFull failed to take this into account. io.ErrUnexpectedEOF is reasonably common when SSL connections go wrong when communicating with ACD, so it manifested itself as transfers from non-encrypted ACD to encrypted ACD getting stuck.
792 lines
20 KiB
Go
792 lines
20 KiB
Go
package crypt
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import (
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"bytes"
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"crypto/aes"
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gocipher "crypto/cipher"
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"crypto/rand"
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"encoding/base32"
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"fmt"
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"io"
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"strings"
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"sync"
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"unicode/utf8"
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"github.com/ncw/rclone/crypt/pkcs7"
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"github.com/pkg/errors"
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"golang.org/x/crypto/nacl/secretbox"
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"golang.org/x/crypto/scrypt"
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"github.com/rfjakob/eme"
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)
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// Constants
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const (
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nameCipherBlockSize = aes.BlockSize
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fileMagic = "RCLONE\x00\x00"
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fileMagicSize = len(fileMagic)
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fileNonceSize = 24
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fileHeaderSize = fileMagicSize + fileNonceSize
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blockHeaderSize = secretbox.Overhead
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blockDataSize = 64 * 1024
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blockSize = blockHeaderSize + blockDataSize
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encryptedSuffix = ".bin" // when file name encryption is off we add this suffix to make sure the cloud provider doesn't process the file
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)
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// Errors returned by cipher
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var (
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ErrorBadDecryptUTF8 = errors.New("bad decryption - utf-8 invalid")
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ErrorBadDecryptControlChar = errors.New("bad decryption - contains control chars")
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ErrorNotAMultipleOfBlocksize = errors.New("not a multiple of blocksize")
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ErrorTooShortAfterDecode = errors.New("too short after base32 decode")
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ErrorEncryptedFileTooShort = errors.New("file is too short to be encrypted")
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ErrorEncryptedFileBadHeader = errors.New("file has truncated block header")
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ErrorEncryptedBadMagic = errors.New("not an encrypted file - bad magic string")
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ErrorEncryptedBadBlock = errors.New("failed to authenticate decrypted block - bad password?")
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ErrorBadBase32Encoding = errors.New("bad base32 filename encoding")
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ErrorFileClosed = errors.New("file already closed")
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ErrorNotAnEncryptedFile = errors.New("not an encrypted file - no \"" + encryptedSuffix + "\" suffix")
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ErrorBadSeek = errors.New("Seek beyond end of file")
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defaultSalt = []byte{0xA8, 0x0D, 0xF4, 0x3A, 0x8F, 0xBD, 0x03, 0x08, 0xA7, 0xCA, 0xB8, 0x3E, 0x58, 0x1F, 0x86, 0xB1}
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)
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// Global variables
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var (
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fileMagicBytes = []byte(fileMagic)
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)
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// ReadSeekCloser is the interface of the read handles
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type ReadSeekCloser interface {
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io.Reader
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io.Seeker
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io.Closer
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}
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// OpenAtOffset opens the file handle at the offset given
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type OpenAtOffset func(offset int64) (io.ReadCloser, error)
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// Cipher is used to swap out the encryption implementations
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type Cipher interface {
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// EncryptFileName encrypts a file path
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EncryptFileName(string) string
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// DecryptFileName decrypts a file path, returns error if decrypt was invalid
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DecryptFileName(string) (string, error)
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// EncryptDirName encrypts a directory path
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EncryptDirName(string) string
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// DecryptDirName decrypts a directory path, returns error if decrypt was invalid
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DecryptDirName(string) (string, error)
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// EncryptData
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EncryptData(io.Reader) (io.Reader, error)
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// DecryptData
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DecryptData(io.ReadCloser) (io.ReadCloser, error)
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// DecryptDataSeek decrypt at a given position
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DecryptDataSeek(open OpenAtOffset, offset int64) (ReadSeekCloser, error)
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// EncryptedSize calculates the size of the data when encrypted
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EncryptedSize(int64) int64
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// DecryptedSize calculates the size of the data when decrypted
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DecryptedSize(int64) (int64, error)
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}
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// NameEncryptionMode is the type of file name encryption in use
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type NameEncryptionMode int
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// NameEncryptionMode levels
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const (
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NameEncryptionOff NameEncryptionMode = iota
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NameEncryptionStandard
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)
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// NewNameEncryptionMode turns a string into a NameEncryptionMode
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func NewNameEncryptionMode(s string) (mode NameEncryptionMode, err error) {
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s = strings.ToLower(s)
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switch s {
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case "off":
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mode = NameEncryptionOff
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case "standard":
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mode = NameEncryptionStandard
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default:
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err = errors.Errorf("Unknown file name encryption mode %q", s)
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}
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return mode, err
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}
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// String turns mode into a human readable string
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func (mode NameEncryptionMode) String() (out string) {
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switch mode {
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case NameEncryptionOff:
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out = "off"
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case NameEncryptionStandard:
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out = "standard"
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default:
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out = fmt.Sprintf("Unknown mode #%d", mode)
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}
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return out
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}
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type cipher struct {
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dataKey [32]byte // Key for secretbox
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nameKey [32]byte // 16,24 or 32 bytes
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nameTweak [nameCipherBlockSize]byte // used to tweak the name crypto
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block gocipher.Block
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mode NameEncryptionMode
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buffers sync.Pool // encrypt/decrypt buffers
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cryptoRand io.Reader // read crypto random numbers from here
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}
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// newCipher initialises the cipher. If salt is "" then it uses a built in salt val
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func newCipher(mode NameEncryptionMode, password, salt string) (*cipher, error) {
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c := &cipher{
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mode: mode,
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cryptoRand: rand.Reader,
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}
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c.buffers.New = func() interface{} {
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return make([]byte, blockSize)
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}
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err := c.Key(password, salt)
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if err != nil {
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return nil, err
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}
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return c, nil
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}
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// Key creates all the internal keys from the password passed in using
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// scrypt.
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//
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// If salt is "" we use a fixed salt just to make attackers lives
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// slighty harder than using no salt.
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//
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// Note that empty passsword makes all 0x00 keys which is used in the
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// tests.
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func (c *cipher) Key(password, salt string) (err error) {
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const keySize = len(c.dataKey) + len(c.nameKey) + len(c.nameTweak)
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var saltBytes = defaultSalt
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if salt != "" {
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saltBytes = []byte(salt)
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}
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var key []byte
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if password == "" {
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key = make([]byte, keySize)
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} else {
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key, err = scrypt.Key([]byte(password), saltBytes, 16384, 8, 1, keySize)
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if err != nil {
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return err
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}
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}
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copy(c.dataKey[:], key)
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copy(c.nameKey[:], key[len(c.dataKey):])
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copy(c.nameTweak[:], key[len(c.dataKey)+len(c.nameKey):])
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// Key the name cipher
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c.block, err = aes.NewCipher(c.nameKey[:])
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return err
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}
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// getBlock gets a block from the pool of size blockSize
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func (c *cipher) getBlock() []byte {
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return c.buffers.Get().([]byte)
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}
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// putBlock returns a block to the pool of size blockSize
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func (c *cipher) putBlock(buf []byte) {
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if len(buf) != blockSize {
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panic("bad blocksize returned to pool")
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}
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c.buffers.Put(buf)
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}
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// check to see if the byte string is valid with no control characters
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// from 0x00 to 0x1F and is a valid UTF-8 string
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func checkValidString(buf []byte) error {
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for i := range buf {
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c := buf[i]
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if c >= 0x00 && c < 0x20 || c == 0x7F {
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return ErrorBadDecryptControlChar
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}
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}
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if !utf8.Valid(buf) {
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return ErrorBadDecryptUTF8
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}
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return nil
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}
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// encodeFileName encodes a filename using a modified version of
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// standard base32 as described in RFC4648
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//
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// The standard encoding is modified in two ways
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// * it becomes lower case (no-one likes upper case filenames!)
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// * we strip the padding character `=`
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func encodeFileName(in []byte) string {
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encoded := base32.HexEncoding.EncodeToString(in)
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encoded = strings.TrimRight(encoded, "=")
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return strings.ToLower(encoded)
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}
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// decodeFileName decodes a filename as encoded by encodeFileName
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func decodeFileName(in string) ([]byte, error) {
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if strings.HasSuffix(in, "=") {
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return nil, ErrorBadBase32Encoding
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}
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// First figure out how many padding characters to add
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roundUpToMultipleOf8 := (len(in) + 7) &^ 7
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equals := roundUpToMultipleOf8 - len(in)
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in = strings.ToUpper(in) + "========"[:equals]
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return base32.HexEncoding.DecodeString(in)
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}
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// encryptSegment encrypts a path segment
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//
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// This uses EME with AES
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//
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// EME (ECB-Mix-ECB) is a wide-block encryption mode presented in the
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// 2003 paper "A Parallelizable Enciphering Mode" by Halevi and
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// Rogaway.
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//
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// This makes for determinstic encryption which is what we want - the
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// same filename must encrypt to the same thing.
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//
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// This means that
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// * filenames with the same name will encrypt the same
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// * filenames which start the same won't have a common prefix
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func (c *cipher) encryptSegment(plaintext string) string {
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if plaintext == "" {
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return ""
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}
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paddedPlaintext := pkcs7.Pad(nameCipherBlockSize, []byte(plaintext))
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ciphertext := eme.Transform(c.block, c.nameTweak[:], paddedPlaintext, eme.DirectionEncrypt)
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return encodeFileName(ciphertext)
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}
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// decryptSegment decrypts a path segment
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func (c *cipher) decryptSegment(ciphertext string) (string, error) {
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if ciphertext == "" {
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return "", nil
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}
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rawCiphertext, err := decodeFileName(ciphertext)
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if err != nil {
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return "", err
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}
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if len(rawCiphertext)%nameCipherBlockSize != 0 {
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return "", ErrorNotAMultipleOfBlocksize
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}
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if len(rawCiphertext) == 0 {
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// not possible if decodeFilename() working correctly
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return "", ErrorTooShortAfterDecode
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}
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paddedPlaintext := eme.Transform(c.block, c.nameTweak[:], rawCiphertext, eme.DirectionDecrypt)
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plaintext, err := pkcs7.Unpad(nameCipherBlockSize, paddedPlaintext)
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if err != nil {
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return "", err
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}
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err = checkValidString(plaintext)
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if err != nil {
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return "", err
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}
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return string(plaintext), err
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}
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// encryptFileName encrypts a file path
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func (c *cipher) encryptFileName(in string) string {
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segments := strings.Split(in, "/")
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for i := range segments {
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segments[i] = c.encryptSegment(segments[i])
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}
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return strings.Join(segments, "/")
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}
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// EncryptFileName encrypts a file path
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func (c *cipher) EncryptFileName(in string) string {
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if c.mode == NameEncryptionOff {
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return in + encryptedSuffix
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}
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return c.encryptFileName(in)
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}
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// EncryptDirName encrypts a directory path
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func (c *cipher) EncryptDirName(in string) string {
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if c.mode == NameEncryptionOff {
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return in
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}
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return c.encryptFileName(in)
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}
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// decryptFileName decrypts a file path
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func (c *cipher) decryptFileName(in string) (string, error) {
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segments := strings.Split(in, "/")
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for i := range segments {
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var err error
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segments[i], err = c.decryptSegment(segments[i])
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if err != nil {
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return "", err
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}
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}
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return strings.Join(segments, "/"), nil
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}
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// DecryptFileName decrypts a file path
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func (c *cipher) DecryptFileName(in string) (string, error) {
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if c.mode == NameEncryptionOff {
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remainingLength := len(in) - len(encryptedSuffix)
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if remainingLength > 0 && strings.HasSuffix(in, encryptedSuffix) {
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return in[:remainingLength], nil
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}
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return "", ErrorNotAnEncryptedFile
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}
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return c.decryptFileName(in)
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}
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// DecryptDirName decrypts a directory path
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func (c *cipher) DecryptDirName(in string) (string, error) {
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if c.mode == NameEncryptionOff {
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return in, nil
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}
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return c.decryptFileName(in)
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}
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// nonce is an NACL secretbox nonce
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type nonce [fileNonceSize]byte
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// pointer returns the nonce as a *[24]byte for secretbox
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func (n *nonce) pointer() *[fileNonceSize]byte {
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return (*[fileNonceSize]byte)(n)
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}
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// fromReader fills the nonce from an io.Reader - normally the OSes
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// crypto random number generator
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func (n *nonce) fromReader(in io.Reader) error {
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read, err := io.ReadFull(in, (*n)[:])
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if read != fileNonceSize {
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return errors.Wrap(err, "short read of nonce")
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}
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return nil
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}
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// fromBuf fills the nonce from the buffer passed in
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func (n *nonce) fromBuf(buf []byte) {
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read := copy((*n)[:], buf)
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if read != fileNonceSize {
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panic("buffer to short to read nonce")
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}
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}
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// carry 1 up the nonce from position i
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func (n *nonce) carry(i int) {
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for ; i < len(*n); i++ {
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digit := (*n)[i]
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newDigit := digit + 1
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(*n)[i] = newDigit
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if newDigit >= digit {
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// exit if no carry
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break
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}
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}
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}
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// increment to add 1 to the nonce
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func (n *nonce) increment() {
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n.carry(0)
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}
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// add an uint64 to the nonce
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func (n *nonce) add(x uint64) {
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carry := uint16(0)
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for i := 0; i < 8; i++ {
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digit := (*n)[i]
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xDigit := byte(x)
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x >>= 8
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carry += uint16(digit) + uint16(xDigit)
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(*n)[i] = byte(carry)
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carry >>= 8
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}
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if carry != 0 {
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n.carry(8)
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}
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}
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// encrypter encrypts an io.Reader on the fly
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type encrypter struct {
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mu sync.Mutex
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in io.Reader
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c *cipher
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nonce nonce
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buf []byte
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readBuf []byte
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bufIndex int
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bufSize int
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err error
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}
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// newEncrypter creates a new file handle encrypting on the fly
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func (c *cipher) newEncrypter(in io.Reader) (*encrypter, error) {
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fh := &encrypter{
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in: in,
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c: c,
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buf: c.getBlock(),
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readBuf: c.getBlock(),
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bufSize: fileHeaderSize,
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}
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// Initialise nonce
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err := fh.nonce.fromReader(c.cryptoRand)
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if err != nil {
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return nil, err
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}
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// Copy magic into buffer
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copy(fh.buf, fileMagicBytes)
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// Copy nonce into buffer
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copy(fh.buf[fileMagicSize:], fh.nonce[:])
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return fh, nil
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}
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// Read as per io.Reader
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func (fh *encrypter) Read(p []byte) (n int, err error) {
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fh.mu.Lock()
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defer fh.mu.Unlock()
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if fh.err != nil {
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return 0, fh.err
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}
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if fh.bufIndex >= fh.bufSize {
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// Read data
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// FIXME should overlap the reads with a go-routine and 2 buffers?
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readBuf := fh.readBuf[:blockDataSize]
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n, err = io.ReadFull(fh.in, readBuf)
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if n == 0 {
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// err can't be nil since:
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// n == len(buf) if and only if err == nil.
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return fh.finish(err)
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}
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// possibly err != nil here, but we will process the
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// data and the next call to ReadFull will return 0, err
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// Write nonce to start of block
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copy(fh.buf, fh.nonce[:])
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// Encrypt the block using the nonce
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block := fh.buf
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secretbox.Seal(block[:0], readBuf[:n], fh.nonce.pointer(), &fh.c.dataKey)
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fh.bufIndex = 0
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fh.bufSize = blockHeaderSize + n
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fh.nonce.increment()
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}
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n = copy(p, fh.buf[fh.bufIndex:fh.bufSize])
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fh.bufIndex += n
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return n, nil
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}
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// finish sets the final error and tidies up
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func (fh *encrypter) finish(err error) (int, error) {
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if fh.err != nil {
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return 0, fh.err
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}
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fh.err = err
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fh.c.putBlock(fh.buf)
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fh.buf = nil
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fh.c.putBlock(fh.readBuf)
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fh.readBuf = nil
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return 0, err
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}
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// Encrypt data encrypts the data stream
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func (c *cipher) EncryptData(in io.Reader) (io.Reader, error) {
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out, err := c.newEncrypter(in)
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if err != nil {
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return nil, err
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}
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return out, nil
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}
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// decrypter decrypts an io.ReaderCloser on the fly
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type decrypter struct {
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mu sync.Mutex
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rc io.ReadCloser
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nonce nonce
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initialNonce nonce
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c *cipher
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buf []byte
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readBuf []byte
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bufIndex int
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bufSize int
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err error
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open OpenAtOffset
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}
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// newDecrypter creates a new file handle decrypting on the fly
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func (c *cipher) newDecrypter(rc io.ReadCloser) (*decrypter, error) {
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fh := &decrypter{
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rc: rc,
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c: c,
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buf: c.getBlock(),
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readBuf: c.getBlock(),
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}
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// Read file header (magic + nonce)
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readBuf := fh.readBuf[:fileHeaderSize]
|
|
_, err := io.ReadFull(fh.rc, readBuf)
|
|
if err == io.EOF || err == io.ErrUnexpectedEOF {
|
|
// This read from 0..fileHeaderSize-1 bytes
|
|
return nil, fh.finishAndClose(ErrorEncryptedFileTooShort)
|
|
} else if err != nil {
|
|
return nil, fh.finishAndClose(err)
|
|
}
|
|
// check the magic
|
|
if !bytes.Equal(readBuf[:fileMagicSize], fileMagicBytes) {
|
|
return nil, fh.finishAndClose(ErrorEncryptedBadMagic)
|
|
}
|
|
// retreive the nonce
|
|
fh.nonce.fromBuf(readBuf[fileMagicSize:])
|
|
fh.initialNonce = fh.nonce
|
|
return fh, nil
|
|
}
|
|
|
|
// newDecrypterSeek creates a new file handle decrypting on the fly
|
|
func (c *cipher) newDecrypterSeek(open OpenAtOffset, offset int64) (fh *decrypter, err error) {
|
|
// Open initially with no seek
|
|
rc, err := open(0)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
// Open the stream which fills in the nonce
|
|
fh, err = c.newDecrypter(rc)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
fh.open = open // will be called by fh.Seek
|
|
if offset != 0 {
|
|
_, err = fh.Seek(offset, 0)
|
|
if err != nil {
|
|
_ = fh.Close()
|
|
return nil, err
|
|
}
|
|
}
|
|
return fh, nil
|
|
}
|
|
|
|
// read data into internal buffer - call with fh.mu held
|
|
func (fh *decrypter) fillBuffer() (err error) {
|
|
// FIXME should overlap the reads with a go-routine and 2 buffers?
|
|
readBuf := fh.readBuf
|
|
n, err := io.ReadFull(fh.rc, readBuf)
|
|
if n == 0 {
|
|
// err can't be nil since:
|
|
// n == len(buf) if and only if err == nil.
|
|
return err
|
|
}
|
|
// possibly err != nil here, but we will process the data and
|
|
// the next call to ReadFull will return 0, err
|
|
|
|
// Check header + 1 byte exists
|
|
if n <= blockHeaderSize {
|
|
if err != nil {
|
|
return err // return pending error as it is likely more accurate
|
|
}
|
|
return ErrorEncryptedFileBadHeader
|
|
}
|
|
// Decrypt the block using the nonce
|
|
block := fh.buf
|
|
_, ok := secretbox.Open(block[:0], readBuf[:n], fh.nonce.pointer(), &fh.c.dataKey)
|
|
if !ok {
|
|
if err != nil {
|
|
return err // return pending error as it is likely more accurate
|
|
}
|
|
return ErrorEncryptedBadBlock
|
|
}
|
|
fh.bufIndex = 0
|
|
fh.bufSize = n - blockHeaderSize
|
|
fh.nonce.increment()
|
|
return nil
|
|
}
|
|
|
|
// Read as per io.Reader
|
|
func (fh *decrypter) Read(p []byte) (n int, err error) {
|
|
fh.mu.Lock()
|
|
defer fh.mu.Unlock()
|
|
|
|
if fh.err != nil {
|
|
return 0, fh.err
|
|
}
|
|
if fh.bufIndex >= fh.bufSize {
|
|
err = fh.fillBuffer()
|
|
if err != nil {
|
|
return 0, fh.finish(err)
|
|
}
|
|
}
|
|
n = copy(p, fh.buf[fh.bufIndex:fh.bufSize])
|
|
fh.bufIndex += n
|
|
return n, nil
|
|
}
|
|
|
|
// Seek as per io.Seeker
|
|
func (fh *decrypter) Seek(offset int64, whence int) (int64, error) {
|
|
fh.mu.Lock()
|
|
defer fh.mu.Unlock()
|
|
|
|
if fh.open == nil {
|
|
return 0, fh.finish(errors.New("can't seek - not initialised with newDecrypterSeek"))
|
|
}
|
|
if whence != 0 {
|
|
return 0, fh.finish(errors.New("can only seek from the start"))
|
|
}
|
|
|
|
// Reset error or return it if not EOF
|
|
if fh.err == io.EOF {
|
|
fh.unFinish()
|
|
} else if fh.err != nil {
|
|
return 0, fh.err
|
|
}
|
|
|
|
// blocks we need to seek, plus bytes we need to discard
|
|
blocks, discard := offset/blockDataSize, offset%blockDataSize
|
|
|
|
// Offset in underlying stream we need to seek
|
|
underlyingOffset := int64(fileHeaderSize) + blocks*(blockHeaderSize+blockDataSize)
|
|
|
|
// Move the nonce on the correct number of blocks from the start
|
|
fh.nonce = fh.initialNonce
|
|
fh.nonce.add(uint64(blocks))
|
|
|
|
// Can we seek underlying stream directly?
|
|
if do, ok := fh.rc.(io.Seeker); ok {
|
|
// Seek underlying stream directly
|
|
_, err := do.Seek(underlyingOffset, 0)
|
|
if err != nil {
|
|
return 0, fh.finish(err)
|
|
}
|
|
} else {
|
|
// if not reopen with seek
|
|
_ = fh.rc.Close() // close underlying file
|
|
fh.rc = nil
|
|
|
|
// Re-open the underlying object with the offset given
|
|
rc, err := fh.open(underlyingOffset)
|
|
if err != nil {
|
|
return 0, fh.finish(errors.Wrap(err, "couldn't reopen file with offset"))
|
|
}
|
|
|
|
// Set the file handle
|
|
fh.rc = rc
|
|
}
|
|
|
|
// Fill the buffer
|
|
err := fh.fillBuffer()
|
|
if err != nil {
|
|
return 0, fh.finish(err)
|
|
}
|
|
|
|
// Discard bytes from the buffer
|
|
if int(discard) > fh.bufSize {
|
|
return 0, fh.finish(ErrorBadSeek)
|
|
}
|
|
fh.bufIndex = int(discard)
|
|
|
|
return offset, nil
|
|
}
|
|
|
|
// finish sets the final error and tidies up
|
|
func (fh *decrypter) finish(err error) error {
|
|
if fh.err != nil {
|
|
return fh.err
|
|
}
|
|
fh.err = err
|
|
fh.c.putBlock(fh.buf)
|
|
fh.buf = nil
|
|
fh.c.putBlock(fh.readBuf)
|
|
fh.readBuf = nil
|
|
return err
|
|
}
|
|
|
|
// unFinish undoes the effects of finish
|
|
func (fh *decrypter) unFinish() {
|
|
// Clear error
|
|
fh.err = nil
|
|
|
|
// reinstate the buffers
|
|
fh.buf = fh.c.getBlock()
|
|
fh.readBuf = fh.c.getBlock()
|
|
|
|
// Empty the buffer
|
|
fh.bufIndex = 0
|
|
fh.bufSize = 0
|
|
}
|
|
|
|
// Close
|
|
func (fh *decrypter) Close() error {
|
|
fh.mu.Lock()
|
|
defer fh.mu.Unlock()
|
|
|
|
// Check already closed
|
|
if fh.err == ErrorFileClosed {
|
|
return fh.err
|
|
}
|
|
// Closed before reading EOF so not finish()ed yet
|
|
if fh.err == nil {
|
|
_ = fh.finish(io.EOF)
|
|
}
|
|
// Show file now closed
|
|
fh.err = ErrorFileClosed
|
|
if fh.rc == nil {
|
|
return nil
|
|
}
|
|
return fh.rc.Close()
|
|
}
|
|
|
|
// finishAndClose does finish then Close()
|
|
//
|
|
// Used when we are returning a nil fh from new
|
|
func (fh *decrypter) finishAndClose(err error) error {
|
|
_ = fh.finish(err)
|
|
_ = fh.Close()
|
|
return err
|
|
}
|
|
|
|
// DecryptData decrypts the data stream
|
|
func (c *cipher) DecryptData(rc io.ReadCloser) (io.ReadCloser, error) {
|
|
out, err := c.newDecrypter(rc)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
return out, nil
|
|
}
|
|
|
|
// DecryptDataSeek decrypts the data stream from offset
|
|
//
|
|
// The open function must return a ReadCloser opened to the offset supplied
|
|
//
|
|
// You must use this form of DecryptData if you might want to Seek the file handle
|
|
func (c *cipher) DecryptDataSeek(open OpenAtOffset, offset int64) (ReadSeekCloser, error) {
|
|
out, err := c.newDecrypterSeek(open, offset)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
return out, nil
|
|
}
|
|
|
|
// EncryptedSize calculates the size of the data when encrypted
|
|
func (c *cipher) EncryptedSize(size int64) int64 {
|
|
blocks, residue := size/blockDataSize, size%blockDataSize
|
|
encryptedSize := int64(fileHeaderSize) + blocks*(blockHeaderSize+blockDataSize)
|
|
if residue != 0 {
|
|
encryptedSize += blockHeaderSize + residue
|
|
}
|
|
return encryptedSize
|
|
}
|
|
|
|
// DecryptedSize calculates the size of the data when decrypted
|
|
func (c *cipher) DecryptedSize(size int64) (int64, error) {
|
|
size -= int64(fileHeaderSize)
|
|
if size < 0 {
|
|
return 0, ErrorEncryptedFileTooShort
|
|
}
|
|
blocks, residue := size/blockSize, size%blockSize
|
|
decryptedSize := blocks * blockDataSize
|
|
if residue != 0 {
|
|
residue -= blockHeaderSize
|
|
if residue <= 0 {
|
|
return 0, ErrorEncryptedFileBadHeader
|
|
}
|
|
}
|
|
decryptedSize += residue
|
|
return decryptedSize, nil
|
|
}
|
|
|
|
// check interfaces
|
|
var (
|
|
_ Cipher = (*cipher)(nil)
|
|
_ io.ReadCloser = (*decrypter)(nil)
|
|
_ io.Reader = (*encrypter)(nil)
|
|
)
|