summaryrefslogtreecommitdiff
path: root/cryptfs/cryptfs_content.go
blob: 0494b69e71b52951441206b68ebaf174ee742ed3 (plain)
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
package cryptfs

// File content encryption / decryption

import (
	"bytes"
	"os"
	"errors"
	"crypto/cipher"
)

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
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 {
		Warn.Printf("DecryptBlock: %s\n", err.Error())
		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]
}