/
stream.go
250 lines (228 loc) · 5.87 KB
/
stream.go
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package crypto
import (
"crypto/cipher"
"crypto/rand"
"crypto/sha512"
"encoding/binary"
"errors"
"io"
"math"
"unsafe"
"golang.org/x/crypto/chacha20poly1305"
"golang.org/x/crypto/curve25519"
"golang.org/x/crypto/hkdf"
)
type writer struct {
dst io.Writer
n int
encBuf []byte
buf []byte // slice of encBuf
err error
aead cipher.AEAD
nonce []byte
nonceRnd []byte // slice of nonce
nonceCnt []byte // slice of nonce, sizeof(counter)
counter uint64
}
// NewWriter implements encryption for an io.Writer object. Encryption is done
// in chunks of bufsiz plaintext. Writing is buffered, and the object should be
// closed to flush remaining buffered plaintext (by encrypting a smaller last
// chunk). The AEAD nonce is 16 bytes randomly generated followed by an 8-byte
// counter (incrementing for each chunk).
//
// Ciphertext size = len(plaintext) + curve25519.ScalarSize + sha512.Size +
// ((len(plaintext) - 1)/bufsiz + 1) * (chacha20poly1305.NonceSizeX +
// poly1305.TagSize).
func NewWriter(w io.Writer, publ []byte, bufsiz int) (io.WriteCloser, error) {
if len(publ) != curve25519.ScalarSize {
return nil, errors.New("bad publ length")
}
ePubl, ePriv, err := newX25519Keypair()
if err != nil {
return nil, err
}
shared, err := curve25519.X25519(ePriv, publ)
if err != nil {
return nil, err
}
// TODO: hkdf-sha512 vs hsalsa20 (from crypto_box)
salt := make([]byte, sha512.Size)
if _, err = rand.Read(salt); err != nil {
return nil, err
}
h := hkdf.New(sha512.New, shared, salt, nil)
key := make([]byte, chacha20poly1305.KeySize)
if _, err = io.ReadFull(h, key); err != nil {
return nil, err
}
aead, err := chacha20poly1305.NewX(key)
if err != nil {
return nil, err
}
if _, err = w.Write(ePubl); err != nil {
return nil, err
}
if _, err = w.Write(salt); err != nil {
return nil, err
}
sw := &writer{
dst: w,
encBuf: make([]byte, bufsiz+aead.Overhead()),
aead: aead,
nonce: make([]byte, aead.NonceSize()),
}
sw.buf = sw.encBuf[:bufsiz]
if len(sw.nonce) < int(unsafe.Sizeof(sw.counter))*2 {
return nil, errors.New("aead nonce cannot safely hold counter")
}
cind := len(sw.nonce) - int(unsafe.Sizeof(sw.counter))
sw.nonceRnd, sw.nonceCnt = sw.nonce[:cind], sw.nonce[cind:]
return sw, nil
}
// Write p to the destination with strict buffering.
func (w *writer) Write(p []byte) (n int, err error) {
// Based on bufio.Writer.Write. Removed large write shortcut to ensure
// all writes are exactly bufsiz except the last one.
for len(p) > len(w.buf)-w.n && w.err == nil {
nn := copy(w.buf[w.n:], p)
w.n += nn
w.flush()
n += nn
p = p[nn:]
}
if w.err != nil {
return n, w.err
}
nn := copy(w.buf[w.n:], p)
w.n += nn
n += nn
return n, nil
}
func (w *writer) flush() {
if w.n == 0 {
return
}
if _, w.err = rand.Read(w.nonceRnd); w.err != nil {
return
}
binary.BigEndian.PutUint64(w.nonceCnt, w.counter)
if w.counter == math.MaxUint64 {
w.err = errors.New("counter overflow, maximum writes exceeded")
return
}
w.counter++
if _, w.err = w.dst.Write(w.nonce); w.err != nil {
return
}
ciphertext := w.aead.Seal(w.encBuf[:0], w.nonce, w.buf[:w.n], nil)
w.n = 0
_, w.err = w.dst.Write(ciphertext)
}
func (w *writer) Close() error {
if w.err != nil {
return w.err
}
w.flush()
if w.err != nil {
return w.err
}
w.err = errors.New("writer closed")
return nil
}
type reader struct {
src io.Reader
plain []byte
// r=read index, w=write index, plain[r:w] is valid
r, w int
aead cipher.AEAD
cipher []byte
cn int
counter uint64
err error
}
// NewReader implements decryption for an io.Reader object. Decryption is done
// in chunks of bufsiz plaintext. Reading is buffered, and only reading until
// EOF is gauranteed to result in an empty ciphertext buffer.
func NewReader(r io.Reader, priv []byte, bufsiz int) (io.Reader, error) {
if len(priv) != curve25519.ScalarSize {
return nil, errors.New("bad priv length")
}
buf := make([]byte, curve25519.ScalarSize+sha512.Size)
if _, err := io.ReadFull(r, buf); err != nil {
return nil, err
}
ePubl, salt := buf[:curve25519.ScalarSize], buf[curve25519.ScalarSize:]
shared, err := curve25519.X25519(priv, ePubl)
if err != nil {
return nil, err
}
h := hkdf.New(sha512.New, shared, salt, nil)
var key []byte
// Try to reuse buf
if len(buf) < chacha20poly1305.KeySize {
key = make([]byte, chacha20poly1305.KeySize)
} else {
key = buf[:chacha20poly1305.KeySize]
}
if _, err = io.ReadFull(h, key); err != nil {
return nil, err
}
aead, err := chacha20poly1305.NewX(key)
return &reader{
src: r,
plain: make([]byte, bufsiz),
aead: aead,
cipher: make([]byte, bufsiz+aead.NonceSize()+aead.Overhead()),
}, nil
}
func (r *reader) Read(p []byte) (int, error) {
var n int
if r.w-r.r > 0 {
// Copy buffered plaintext
n += copy(p, r.plain[r.r:r.w])
p = p[n:]
r.r += n
}
if len(p) == 0 || r.err != nil {
return n, r.err
}
var nn int
nn, r.err = r.src.Read(r.cipher[r.cn:])
r.cn += nn
if r.cn < len(r.cipher) && r.err != io.EOF {
// Under-read but the stream hasn't ended.
return n, r.err
}
if r.cn < r.aead.NonceSize()+r.aead.Overhead() {
if r.err == io.EOF {
r.err = io.ErrUnexpectedEOF
}
return n, r.err
}
ciphertext := r.cipher[:r.cn]
nonce := ciphertext[:r.aead.NonceSize()]
counter := nonce[len(nonce)-8:]
ciphertext = ciphertext[r.aead.NonceSize():]
if binary.BigEndian.Uint64(counter) != r.counter {
r.err = errors.New("invalid nonce counter")
return n, r.err
}
if r.counter == math.MaxUint64 {
r.err = errors.New("counter overflow, maximum writes exceeded")
return n, r.err
}
r.counter++
r.plain, r.err = r.aead.Open(r.plain[:0], nonce, ciphertext, nil)
r.r = 0
r.w = len(r.plain)
r.plain = r.plain[:cap(r.plain)]
// Only the last block may be truncated, set EOF to avoid reading more.
if r.cn < len(r.cipher) {
r.err = io.EOF
}
r.cn = 0
nn = copy(p, r.plain[r.r:r.w])
n += nn
r.r += nn
return n, r.err
}