1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
// 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/openpgp/error"
"crypto/sha1"
"crypto/subtle"
"hash"
"io"
"os"
"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
}
func (se *SymmetricallyEncrypted) parse(r io.Reader) os.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] != 1 {
return error.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, os.Error) {
keySize := c.keySize()
if keySize == 0 {
return nil, error.UnsupportedError("unknown cipher: " + strconv.Itoa(int(c)))
}
if len(key) != keySize {
return nil, error.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, error.InvalidArgumentError("can't try ciphers with different block lengths")
}
ocfbResync := cipher.OCFBResync
if se.MDC {
// MDC packets use a different form of OCFB mode.
ocfbResync = cipher.OCFBNoResync
}
s := cipher.NewOCFBDecrypter(c.new(key), se.prefix, ocfbResync)
if s == nil {
return nil, error.KeyIncorrectError
}
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, os.Error) {
return ser.in.Read(buf)
}
func (ser seReader) Close() os.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 os.Error) {
if ser.error {
err = io.ErrUnexpectedEOF
return
}
if ser.eof {
err = os.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 == os.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 = os.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 == os.EOF {
ser.eof = true
}
return
}
func (ser *seMDCReader) Close() os.Error {
if ser.error {
return error.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 == os.EOF {
break
}
if err != nil {
return error.SignatureError("error during reading")
}
}
// This is a new-format packet tag byte for a type 19 (MDC) packet.
const mdcPacketTagByte = byte(0x80) | 0x40 | 19
if ser.trailer[0] != mdcPacketTagByte || ser.trailer[1] != sha1.Size {
return error.SignatureError("MDC packet not found")
}
ser.h.Write(ser.trailer[:2])
final := ser.h.Sum()
if subtle.ConstantTimeCompare(final, ser.trailer[2:]) == 1 {
return error.SignatureError("hash mismatch")
}
return nil
}