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
|
package cryptfs
// File content encryption / decryption
import (
"bytes"
"os"
"errors"
"crypto/cipher"
"crypto/md5"
"encoding/hex"
)
const (
// A block of 4124 zero bytes has this md5
ZeroBlockMd5 = "64331af89bd15a987b39855338336237"
)
// md5sum - debug helper, return md5 hex string
func md5sum(buf []byte) string {
rawHash := md5.Sum(buf)
hash := hex.EncodeToString(rawHash[:])
return hash
}
type CryptFile struct {
file *os.File
gcm cipher.AEAD
}
// DecryptBlocks - Decrypt a number of blocks
func (be *CryptFS) DecryptBlocks(ciphertext []byte) ([]byte, error) {
cBuf := bytes.NewBuffer(ciphertext)
var err error
var pBuf bytes.Buffer
for cBuf.Len() > 0 {
cBlock := cBuf.Next(int(be.cipherBS))
var pBlock []byte
pBlock, err = be.DecryptBlock(cBlock)
if err != nil {
break
}
pBuf.Write(pBlock)
}
return pBuf.Bytes(), err
}
// DecryptBlock - Verify and decrypt GCM block
//
// Corner case: A full-sized block of all-zero ciphertext bytes is translated
// to an all-zero plaintext block, i.e. file hole passtrough.
func (be *CryptFS) DecryptBlock(ciphertext []byte) ([]byte, error) {
// Empty block?
if len(ciphertext) == 0 {
return ciphertext, nil
}
// All-zero block?
if bytes.Equal(ciphertext, be.allZeroBlock) {
Debug.Printf("DecryptBlock: file hole encountered\n")
return make([]byte, be.plainBS), 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]
ciphertextOrig := ciphertext
ciphertext = ciphertext[NONCE_LEN:]
// Decrypt
var plaintext []byte
plaintext, err := be.gcm.Open(plaintext, nonce, ciphertext, nil)
if err != nil {
Warn.Printf("DecryptBlock: %s, len=%d, md5=%s\n", err.Error(), len(ciphertextOrig), Warn.Md5sum(ciphertextOrig))
Debug.Println(hex.Dump(ciphertextOrig))
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
}
// Split a plaintext byte range into (possibly partial) blocks
func (be *CryptFS) SplitRange(offset uint64, length uint64) []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.minu64(length, be.plainBS - b.Offset)
parts = append(parts, b)
offset += b.Length
length -= b.Length
}
return parts
}
// PlainSize - calculate plaintext size from ciphertext size
func (be *CryptFS) PlainSize(size uint64) uint64 {
// Zero sized files stay zero-sized
if size == 0 {
return 0
}
overhead := be.cipherBS - be.plainBS
nBlocks := (size + be.cipherBS - 1) / be.cipherBS
if nBlocks * overhead > size {
Warn.Printf("PlainSize: Negative size, returning 0 instead\n")
return 0
}
size -= nBlocks * overhead
return size
}
// CipherSize - calculate ciphertext size from plaintext size
func (be *CryptFS) CipherSize(size uint64) uint64 {
overhead := be.cipherBS - be.plainBS
nBlocks := (size + be.plainBS - 1) / be.plainBS
size += nBlocks * overhead
return size
}
func (be *CryptFS) minu64(x uint64, y uint64) uint64 {
if x < y {
return x
}
return y
}
// CiphertextRange - Get byte range in backing ciphertext corresponding
// to plaintext range. Returns a range aligned to ciphertext blocks.
func (be *CryptFS) CiphertextRange(offset uint64, length uint64) (alignedOffset uint64, alignedLength uint64, skipBytes int) {
// Decrypting the ciphertext will yield too many plaintext bytes. Skip this number
// of bytes from the front.
skip := offset % be.plainBS
firstBlockNo := offset / be.plainBS
lastBlockNo := ( offset + length - 1 ) / be.plainBS
alignedOffset = firstBlockNo * be.cipherBS
alignedLength = (lastBlockNo - firstBlockNo + 1) * be.cipherBS
skipBytes = int(skip)
return alignedOffset, alignedLength, skipBytes
}
// Get the byte range in the ciphertext corresponding to blocks
// (full blocks!)
func (be *CryptFS) JoinCiphertextRange(blocks []intraBlock) (uint64, uint64) {
offset, _ := blocks[0].CiphertextRange()
last := blocks[len(blocks)-1]
length := (last.BlockNo - blocks[0].BlockNo + 1) * be.cipherBS
return offset, length
}
// Crop plaintext that correspons to complete cipher blocks down to what is
// requested according to "iblocks"
func (be *CryptFS) CropPlaintext(plaintext []byte, blocks []intraBlock) []byte {
offset := blocks[0].Offset
last := blocks[len(blocks)-1]
length := (last.BlockNo - blocks[0].BlockNo + 1) * be.plainBS
var cropped []byte
if offset + length > uint64(len(plaintext)) {
cropped = plaintext[offset:len(plaintext)]
} else {
cropped = plaintext[offset:offset+length]
}
return cropped
}
// MergeBlocks - Merge newData into oldData at offset
// New block may be bigger than both newData and oldData
func (be *CryptFS) MergeBlocks(oldData []byte, newData []byte, offset int) []byte {
// Make block of maximum size
out := make([]byte, be.plainBS)
// Copy old and new data into it
copy(out, oldData)
l := len(newData)
copy(out[offset:offset + l], newData)
// Crop to length
outLen := len(oldData)
newLen := offset + len(newData)
if outLen < newLen {
outLen = newLen
}
return out[0:outLen]
}
|
