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|
package main
import (
"bufio"
"bytes"
"crypto/cipher"
"crypto/rand"
"errors"
"io"
"golang.org/x/crypto/chacha20poly1305"
)
const (
nonceSize = chacha20poly1305.NonceSize
aeadOverhead = chacha20poly1305.Overhead
segmentSize = 1024 * 1024
plaintextSegmentSize = segmentSize - aeadOverhead
saltSize = 16
)
type segmentEncrypter struct {
password string
aead cipher.AEAD
nonce [nonceSize]byte
}
func (se *segmentEncrypter) initialize(salt []byte) error {
key := hashPassword(se.password, salt)
var err error
se.aead, err = chacha20poly1305.New(key)
return err
}
func (se *segmentEncrypter) ad(lastSegment bool) []byte {
// Increment counter
for i := 0; ; i++ {
if i == len(se.nonce) {
panic("counter overflowed")
}
se.nonce[i]++
if se.nonce[i] != 0 {
break
}
}
if lastSegment {
return []byte{1}
}
return []byte{0}
}
func (se *segmentEncrypter) encrypt(out, buf []byte, lastSegment bool) []byte {
ad := se.ad(lastSegment)
return se.aead.Seal(out, se.nonce[:], buf, ad)
}
func (se *segmentEncrypter) decrypt(out, buf []byte, lastSegment bool) ([]byte, error) {
ad := se.ad(lastSegment)
return se.aead.Open(out, se.nonce[:], buf, ad)
}
type encryptingWriter struct {
w io.Writer
encrypter segmentEncrypter
buf []byte
initialized bool
}
func newEncryptingWriter(w io.Writer, password string) *encryptingWriter {
return &encryptingWriter{
w: w,
encrypter: segmentEncrypter{
password: password,
},
}
}
func (w *encryptingWriter) initialize() error {
if w.initialized {
return nil
}
header := make([]byte, saltSize)
rand.Read(header)
if err := w.encrypter.initialize(header); err != nil {
return err
}
if _, err := w.w.Write(header); err != nil {
return err
}
w.buf = make([]byte, 0, segmentSize)
w.initialized = true
return nil
}
func (w *encryptingWriter) writeBuf(lastSegment bool) error {
if _, err := w.w.Write(w.encrypter.encrypt(w.buf[:0], w.buf, lastSegment)); err != nil {
return err
}
w.buf = w.buf[:0]
return nil
}
func (w *encryptingWriter) Write(buf []byte) (int, error) {
if err := w.initialize(); err != nil {
return 0, err
}
nn := 0
for len(buf) > 0 {
if len(w.buf) == plaintextSegmentSize {
if err := w.writeBuf(false); err != nil {
return nn, err
}
}
n := copy(w.buf[len(w.buf):plaintextSegmentSize], buf)
nn += n
w.buf = w.buf[:len(w.buf)+n]
buf = buf[n:]
}
return nn, nil
}
func (w *encryptingWriter) close() error {
if err := w.initialize(); err != nil {
return err
}
return w.writeBuf(true)
}
func (w *encryptingWriter) ReadFrom(r io.Reader) (int64, error) {
if err := w.initialize(); err != nil {
return 0, err
}
var nn int64
for {
n, err := io.ReadFull(r, w.buf[len(w.buf):plaintextSegmentSize+1])
nn += int64(n)
w.buf = w.buf[:len(w.buf)+n]
if err != nil {
if err == io.EOF || err == io.ErrUnexpectedEOF {
return nn, nil
}
return nn, err
}
nextByte := w.buf[plaintextSegmentSize]
w.buf = w.buf[:plaintextSegmentSize]
if err := w.writeBuf(false); err != nil {
return nn, err
}
w.buf = w.buf[:1]
w.buf[0] = nextByte
}
}
type decryptingReader struct {
r *bufio.Reader
decrypter segmentEncrypter
buf bytes.Buffer
initialized bool
readFinalBlock bool
}
func newDecryptingReader(r io.Reader, password string) *decryptingReader {
return &decryptingReader{
r: bufio.NewReaderSize(r, 0), // we only need .UnreadByte
decrypter: segmentEncrypter{
password: password,
},
}
}
func (r *decryptingReader) initialize() error {
if r.initialized {
return nil
}
header := make([]byte, saltSize)
if _, err := io.ReadFull(r.r, header); err != nil {
if err == io.EOF {
return io.ErrUnexpectedEOF
}
return err
}
if err := r.decrypter.initialize(header); err != nil {
return err
}
r.buf = *bytes.NewBuffer(make([]byte, 0, segmentSize+1))
r.initialized = true
return nil
}
func (r *decryptingReader) fillBuf() error {
r.buf.Reset()
// Read 1 extra byte to make sure if we're at EOF.
buf := r.buf.AvailableBuffer()[:segmentSize+1]
n, err := io.ReadFull(r.r, buf)
if err == io.ErrUnexpectedEOF {
r.readFinalBlock = true
} else if err != nil {
if err == io.EOF && !r.readFinalBlock {
return errors.New("premature EOF")
}
return err
}
buf = buf[:n]
if len(buf) == int(segmentSize)+1 {
r.r.UnreadByte()
buf = buf[:segmentSize]
}
buf, err = r.decrypter.decrypt(buf[:0], buf, r.readFinalBlock)
if err != nil {
return err
}
r.buf.Write(buf)
return nil
}
func (r *decryptingReader) Read(buf []byte) (int, error) {
if err := r.initialize(); err != nil {
return 0, err
}
if r.buf.Len() == 0 {
if err := r.fillBuf(); err != nil {
return 0, err
}
}
return r.buf.Read(buf)
}
func (r *decryptingReader) WriteTo(w io.Writer) (int64, error) {
if err := r.initialize(); err != nil {
return 0, err
}
var nn int64
for {
n, err := r.buf.WriteTo(w)
nn += n
if err != nil {
return nn, err
}
if err := r.fillBuf(); err != nil {
if err == io.EOF {
return nn, nil
}
return nn, err
}
}
}
|
