--- /dev/null
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package packet
+
+import (
+ "crypto/cipher"
+ "crypto/sha1"
+ "crypto/subtle"
+ "golang.org/x/crypto/openpgp/errors"
+ "hash"
+ "io"
+ "strconv"
+)
+
+// SymmetricallyEncrypted represents a symmetrically encrypted byte string. The
+// encrypted contents will consist of more OpenPGP packets. See RFC 4880,
+// sections 5.7 and 5.13.
+type SymmetricallyEncrypted struct {
+ MDC bool // true iff this is a type 18 packet and thus has an embedded MAC.
+ contents io.Reader
+ prefix []byte
+}
+
+const symmetricallyEncryptedVersion = 1
+
+func (se *SymmetricallyEncrypted) parse(r io.Reader) error {
+ if se.MDC {
+ // See RFC 4880, section 5.13.
+ var buf [1]byte
+ _, err := readFull(r, buf[:])
+ if err != nil {
+ return err
+ }
+ if buf[0] != symmetricallyEncryptedVersion {
+ return errors.UnsupportedError("unknown SymmetricallyEncrypted version")
+ }
+ }
+ se.contents = r
+ return nil
+}
+
+// Decrypt returns a ReadCloser, from which the decrypted contents of the
+// packet can be read. An incorrect key can, with high probability, be detected
+// immediately and this will result in a KeyIncorrect error being returned.
+func (se *SymmetricallyEncrypted) Decrypt(c CipherFunction, key []byte) (io.ReadCloser, error) {
+ keySize := c.KeySize()
+ if keySize == 0 {
+ return nil, errors.UnsupportedError("unknown cipher: " + strconv.Itoa(int(c)))
+ }
+ if len(key) != keySize {
+ return nil, errors.InvalidArgumentError("SymmetricallyEncrypted: incorrect key length")
+ }
+
+ if se.prefix == nil {
+ se.prefix = make([]byte, c.blockSize()+2)
+ _, err := readFull(se.contents, se.prefix)
+ if err != nil {
+ return nil, err
+ }
+ } else if len(se.prefix) != c.blockSize()+2 {
+ return nil, errors.InvalidArgumentError("can't try ciphers with different block lengths")
+ }
+
+ ocfbResync := OCFBResync
+ if se.MDC {
+ // MDC packets use a different form of OCFB mode.
+ ocfbResync = OCFBNoResync
+ }
+
+ s := NewOCFBDecrypter(c.new(key), se.prefix, ocfbResync)
+ if s == nil {
+ return nil, errors.ErrKeyIncorrect
+ }
+
+ plaintext := cipher.StreamReader{S: s, R: se.contents}
+
+ if se.MDC {
+ // MDC packets have an embedded hash that we need to check.
+ h := sha1.New()
+ h.Write(se.prefix)
+ return &seMDCReader{in: plaintext, h: h}, nil
+ }
+
+ // Otherwise, we just need to wrap plaintext so that it's a valid ReadCloser.
+ return seReader{plaintext}, nil
+}
+
+// seReader wraps an io.Reader with a no-op Close method.
+type seReader struct {
+ in io.Reader
+}
+
+func (ser seReader) Read(buf []byte) (int, error) {
+ return ser.in.Read(buf)
+}
+
+func (ser seReader) Close() error {
+ return nil
+}
+
+const mdcTrailerSize = 1 /* tag byte */ + 1 /* length byte */ + sha1.Size
+
+// An seMDCReader wraps an io.Reader, maintains a running hash and keeps hold
+// of the most recent 22 bytes (mdcTrailerSize). Upon EOF, those bytes form an
+// MDC packet containing a hash of the previous contents which is checked
+// against the running hash. See RFC 4880, section 5.13.
+type seMDCReader struct {
+ in io.Reader
+ h hash.Hash
+ trailer [mdcTrailerSize]byte
+ scratch [mdcTrailerSize]byte
+ trailerUsed int
+ error bool
+ eof bool
+}
+
+func (ser *seMDCReader) Read(buf []byte) (n int, err error) {
+ if ser.error {
+ err = io.ErrUnexpectedEOF
+ return
+ }
+ if ser.eof {
+ err = io.EOF
+ return
+ }
+
+ // If we haven't yet filled the trailer buffer then we must do that
+ // first.
+ for ser.trailerUsed < mdcTrailerSize {
+ n, err = ser.in.Read(ser.trailer[ser.trailerUsed:])
+ ser.trailerUsed += n
+ if err == io.EOF {
+ if ser.trailerUsed != mdcTrailerSize {
+ n = 0
+ err = io.ErrUnexpectedEOF
+ ser.error = true
+ return
+ }
+ ser.eof = true
+ n = 0
+ return
+ }
+
+ if err != nil {
+ n = 0
+ return
+ }
+ }
+
+ // If it's a short read then we read into a temporary buffer and shift
+ // the data into the caller's buffer.
+ if len(buf) <= mdcTrailerSize {
+ n, err = readFull(ser.in, ser.scratch[:len(buf)])
+ copy(buf, ser.trailer[:n])
+ ser.h.Write(buf[:n])
+ copy(ser.trailer[:], ser.trailer[n:])
+ copy(ser.trailer[mdcTrailerSize-n:], ser.scratch[:])
+ if n < len(buf) {
+ ser.eof = true
+ err = io.EOF
+ }
+ return
+ }
+
+ n, err = ser.in.Read(buf[mdcTrailerSize:])
+ copy(buf, ser.trailer[:])
+ ser.h.Write(buf[:n])
+ copy(ser.trailer[:], buf[n:])
+
+ if err == io.EOF {
+ ser.eof = true
+ }
+ return
+}
+
+// This is a new-format packet tag byte for a type 19 (MDC) packet.
+const mdcPacketTagByte = byte(0x80) | 0x40 | 19
+
+func (ser *seMDCReader) Close() error {
+ if ser.error {
+ return errors.SignatureError("error during reading")
+ }
+
+ for !ser.eof {
+ // We haven't seen EOF so we need to read to the end
+ var buf [1024]byte
+ _, err := ser.Read(buf[:])
+ if err == io.EOF {
+ break
+ }
+ if err != nil {
+ return errors.SignatureError("error during reading")
+ }
+ }
+
+ if ser.trailer[0] != mdcPacketTagByte || ser.trailer[1] != sha1.Size {
+ return errors.SignatureError("MDC packet not found")
+ }
+ ser.h.Write(ser.trailer[:2])
+
+ final := ser.h.Sum(nil)
+ if subtle.ConstantTimeCompare(final, ser.trailer[2:]) != 1 {
+ return errors.SignatureError("hash mismatch")
+ }
+ return nil
+}
+
+// An seMDCWriter writes through to an io.WriteCloser while maintains a running
+// hash of the data written. On close, it emits an MDC packet containing the
+// running hash.
+type seMDCWriter struct {
+ w io.WriteCloser
+ h hash.Hash
+}
+
+func (w *seMDCWriter) Write(buf []byte) (n int, err error) {
+ w.h.Write(buf)
+ return w.w.Write(buf)
+}
+
+func (w *seMDCWriter) Close() (err error) {
+ var buf [mdcTrailerSize]byte
+
+ buf[0] = mdcPacketTagByte
+ buf[1] = sha1.Size
+ w.h.Write(buf[:2])
+ digest := w.h.Sum(nil)
+ copy(buf[2:], digest)
+
+ _, err = w.w.Write(buf[:])
+ if err != nil {
+ return
+ }
+ return w.w.Close()
+}
+
+// noOpCloser is like an ioutil.NopCloser, but for an io.Writer.
+type noOpCloser struct {
+ w io.Writer
+}
+
+func (c noOpCloser) Write(data []byte) (n int, err error) {
+ return c.w.Write(data)
+}
+
+func (c noOpCloser) Close() error {
+ return nil
+}
+
+// SerializeSymmetricallyEncrypted serializes a symmetrically encrypted packet
+// to w and returns a WriteCloser to which the to-be-encrypted packets can be
+// written.
+// If config is nil, sensible defaults will be used.
+func SerializeSymmetricallyEncrypted(w io.Writer, c CipherFunction, key []byte, config *Config) (contents io.WriteCloser, err error) {
+ if c.KeySize() != len(key) {
+ return nil, errors.InvalidArgumentError("SymmetricallyEncrypted.Serialize: bad key length")
+ }
+ writeCloser := noOpCloser{w}
+ ciphertext, err := serializeStreamHeader(writeCloser, packetTypeSymmetricallyEncryptedMDC)
+ if err != nil {
+ return
+ }
+
+ _, err = ciphertext.Write([]byte{symmetricallyEncryptedVersion})
+ if err != nil {
+ return
+ }
+
+ block := c.new(key)
+ blockSize := block.BlockSize()
+ iv := make([]byte, blockSize)
+ _, err = config.Random().Read(iv)
+ if err != nil {
+ return
+ }
+ s, prefix := NewOCFBEncrypter(block, iv, OCFBNoResync)
+ _, err = ciphertext.Write(prefix)
+ if err != nil {
+ return
+ }
+ plaintext := cipher.StreamWriter{S: s, W: ciphertext}
+
+ h := sha1.New()
+ h.Write(iv)
+ h.Write(iv[blockSize-2:])
+ contents = &seMDCWriter{w: plaintext, h: h}
+ return
+}
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