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
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
|
package cryptfs
import (
"fmt"
"os"
"io"
"errors"
"crypto/cipher"
)
type CryptFile struct {
file *os.File
gcm cipher.AEAD
plainBS int64
cipherBS int64
}
// decryptBlock - Verify and decrypt GCM block
func (be *CryptFS) DecryptBlock(ciphertext []byte) ([]byte, error) {
// Empty block?
if len(ciphertext) == 0 {
return ciphertext, nil
}
if len(ciphertext) < NONCE_LEN {
warn.Printf("decryptBlock: Block is too short: %d bytes\n", len(ciphertext))
return nil, errors.New("Block is too short")
}
// Extract nonce
nonce := ciphertext[:NONCE_LEN]
ciphertext = ciphertext[NONCE_LEN:]
// Decrypt
var plaintext []byte
plaintext, err := be.gcm.Open(plaintext, nonce, ciphertext, nil)
if err != nil {
return nil, err
}
return plaintext, nil
}
// encryptBlock - Encrypt and add MAC using GCM
func (be *CryptFS) EncryptBlock(plaintext []byte) []byte {
// Empty block?
if len(plaintext) == 0 {
return plaintext
}
// Get fresh nonce
nonce := gcmNonce.Get()
// Encrypt plaintext and append to nonce
ciphertext := be.gcm.Seal(nonce, nonce, plaintext, nil)
return ciphertext
}
// readCipherBlock - Read ciphertext block number "blockNo", decrypt,
// return plaintext
func (be *CryptFile) readCipherBlock(blockNo int64) ([]byte, error) {
off := blockNo * int64(be.cipherBS)
buf := make([]byte, be.cipherBS)
readN, err := be.file.ReadAt(buf, off)
if err != nil && err != io.EOF {
return nil, err
}
// Truncate buffer to actually read bytes
buf = buf[:readN]
// Empty block?
if len(buf) == 0 {
return buf, nil
}
if len(buf) < NONCE_LEN {
warn.Printf("readCipherBlock: Block is too short: %d bytes\n", len(buf))
return nil, errors.New("Block is too short")
}
// Extract nonce
nonce := buf[:NONCE_LEN]
buf = buf[NONCE_LEN:]
// Decrypt
var plainBuf []byte
plainBuf, err = be.gcm.Open(plainBuf, nonce, buf, nil)
if err != nil {
fmt.Printf("gcm.Open() failed: %d\n", err)
return nil, err
}
return plainBuf, nil
}
// intraBlock identifies a part of a file block
type intraBlock struct {
BlockNo int64 // Block number in file
Offset int64 // Offset into block plaintext
Length int64 // Length of data from this block
fs *CryptFS
}
// isPartial - is the block partial? This means we have to do read-modify-write.
func (ib *intraBlock) IsPartial() bool {
if ib.Offset > 0 || ib.Length < ib.fs.plainBS {
return true
}
return false
}
// CiphertextRange - get byte range in ciphertext file corresponding to BlockNo
// (complete block)
func (ib *intraBlock) CiphertextRange() (offset int64, length int64) {
return ib.BlockNo * ib.fs.cipherBS, ib.fs.cipherBS
}
// PlaintextRange - get byte range in plaintext corresponding to BlockNo
// (complete block)
func (ib *intraBlock) PlaintextRange() (offset int64, length int64) {
return ib.BlockNo * ib.fs.plainBS, ib.fs.plainBS
}
// CropBlock - crop a potentially larger plaintext block down to the relevant part
func (ib *intraBlock) CropBlock(d []byte) []byte{
lenHave := len(d)
lenWant := int(ib.Offset+ib.Length)
if lenHave < lenWant {
return d[ib.Offset:lenHave]
}
return d[ib.Offset:lenWant]
}
// Split a plaintext byte range into (possible partial) blocks
func (be *CryptFS) SplitRange(offset int64, length int64) []intraBlock {
var b intraBlock
var parts []intraBlock
b.fs = be
for length > 0 {
b.BlockNo = offset / be.plainBS
b.Offset = offset % be.plainBS
b.Length = be.min64(length, be.plainBS - b.Offset)
parts = append(parts, b)
offset += b.Length
length -= b.Length
}
return parts
}
func (be *CryptFS) min64(x int64, y int64) int64 {
if x < y {
return x
}
return y
}
// writeCipherBlock - Encrypt plaintext and write it to file block "blockNo"
func (be *CryptFile) writeCipherBlock(blockNo int64, plain []byte) error {
if int64(len(plain)) > be.plainBS {
panic("writeCipherBlock: Cannot write block that is larger than plainBS")
}
// Get fresh nonce
nonce := gcmNonce.Get()
// Encrypt data and append to nonce
cipherBuf := be.gcm.Seal(nonce, nonce, plain, nil)
// WriteAt retries short writes autmatically
written, err := be.file.WriteAt(cipherBuf, blockNo * be.cipherBS)
debug.Printf("writeCipherBlock: wrote %d ciphertext bytes to block %d\n",
written, blockNo)
return err
}
// Perform RMW cycle on block
// Write "data" into file location specified in "b"
func (be *CryptFile) rmwWrite(b intraBlock, data []byte, f *os.File) error {
if b.Length != int64(len(data)) {
panic("Length mismatch")
}
oldBlock, err := be.readCipherBlock(b.BlockNo)
if err != nil {
return err
}
newBlockLen := b.Offset + b.Length
debug.Printf("newBlockLen := %d + %d\n", b.Offset, b.Length)
var newBlock []byte
// Write goes beyond the old block and grows the file?
// Must create a bigger newBlock
if newBlockLen > int64(len(oldBlock)) {
newBlock = make([]byte, newBlockLen)
} else {
newBlock = make([]byte, len(oldBlock))
}
// Fill with old data
copy(newBlock, oldBlock)
// Then overwrite the relevant parts with new data
copy(newBlock[b.Offset:b.Offset + b.Length], data)
// Actual write
err = be.writeCipherBlock(b.BlockNo, newBlock)
if err != nil {
// An incomplete write to a ciphertext block means that the whole block
// is destroyed.
fmt.Printf("rmwWrite: Write error: %s\n", err)
}
return err
}
|
