1. 1
2. 2
3. 3
4. 4
5. 5
6. 6
7. 7
8. 8
9. 9
10. 10
11. 11
12. 12
13. 13
14. 14
15. 15
16. 16
17. 17
18. 18
19. 19
20. 20
21. 21
22. 22
23. 23
24. 24
25. 25
26. 26
27. 27
28. 28
29. 29
30. 30
31. 31
32. 32
33. 33
34. 34
35. 35
36. 36
37. 37
38. 38
39. 39
40. 40
41. 41
42. 42
43. 43
44. 44
45. 45
46. 46
47. 47
48. 48
49. 49
50. 50
51. 51
52. 52
53. 53
54. 54
55. 55
56. 56
57. 57
58. 58
59. 59
60. 60
61. 61
62. 62
63. 63
64. 64
65. 65
66. 66
67. 67
68. 68
69. 69
70. 70
71. 71
72. 72
73. 73
74. 74
75. 75
76. 76
77. 77
78. 78
79. 79
80. 80
81. 81
82. 82
83. 83
84. 84
85. 85
86. 86
87. 87
88. 88
89. 89
90. 90
91. 91
92. 92
93. 93
94. 94
95. 95
96. 96
97. 97
98. 98
99. 99
100. 100
101. 101
102. 102
103. 103
104. 104
105. 105
106. 106
107. 107
108. 108
109. 109
110. 110
111. 111
112. 112
113. 113
114. 114
115. 115
116. 116
117. 117
118. 118
119. 119
120. 120
121. 121
122. 122
123. 123
124. 124
125. 125
126. 126
127. 127
128. 128
129. 129
130. 130
131. 131
132. 132
133. 133
134. 134
135. 135
136. 136
137. 137
138. 138
139. 139
140. 140
141. 141
142. 142
143. 143

// Copyright 2010 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.

// OpenPGP CFB Mode. http://tools.ietf.org/html/rfc4880#section-13.9

package packet

import (
	"crypto/cipher"
)

type ocfbEncrypter struct {
	b       cipher.Block
	fre     []byte
	outUsed int
}

// An OCFBResyncOption determines if the "resynchronization step" of OCFB is
// performed.
type OCFBResyncOption bool

const (
	OCFBResync   OCFBResyncOption = true
	OCFBNoResync OCFBResyncOption = false
)

// NewOCFBEncrypter returns a cipher.Stream which encrypts data with OpenPGP's
// cipher feedback mode using the given cipher.Block, and an initial amount of
// ciphertext.  randData must be random bytes and be the same length as the
// cipher.Block's block size. Resync determines if the "resynchronization step"
// from RFC 4880, 13.9 step 7 is performed. Different parts of OpenPGP vary on
// this point.
func NewOCFBEncrypter(block cipher.Block, randData []byte, resync OCFBResyncOption) (cipher.Stream, []byte) {
	blockSize := block.BlockSize()
	if len(randData) != blockSize {
		return nil, nil
	}

	x := &ocfbEncrypter{
		b:       block,
		fre:     make([]byte, blockSize),
		outUsed: 0,
	}
	prefix := make([]byte, blockSize+2)

	block.Encrypt(x.fre, x.fre)
	for i := 0; i < blockSize; i++ {
		prefix[i] = randData[i] ^ x.fre[i]
	}

	block.Encrypt(x.fre, prefix[:blockSize])
	prefix[blockSize] = x.fre[0] ^ randData[blockSize-2]
	prefix[blockSize+1] = x.fre[1] ^ randData[blockSize-1]

	if resync {
		block.Encrypt(x.fre, prefix[2:])
	} else {
		x.fre[0] = prefix[blockSize]
		x.fre[1] = prefix[blockSize+1]
		x.outUsed = 2
	}
	return x, prefix
}

func (x *ocfbEncrypter) XORKeyStream(dst, src []byte) {
	for i := 0; i < len(src); i++ {
		if x.outUsed == len(x.fre) {
			x.b.Encrypt(x.fre, x.fre)
			x.outUsed = 0
		}

		x.fre[x.outUsed] ^= src[i]
		dst[i] = x.fre[x.outUsed]
		x.outUsed++
	}
}

type ocfbDecrypter struct {
	b       cipher.Block
	fre     []byte
	outUsed int
}

// NewOCFBDecrypter returns a cipher.Stream which decrypts data with OpenPGP's
// cipher feedback mode using the given cipher.Block. Prefix must be the first
// blockSize + 2 bytes of the ciphertext, where blockSize is the cipher.Block's
// block size. If an incorrect key is detected then nil is returned. On
// successful exit, blockSize+2 bytes of decrypted data are written into
// prefix. Resync determines if the "resynchronization step" from RFC 4880,
// 13.9 step 7 is performed. Different parts of OpenPGP vary on this point.
func NewOCFBDecrypter(block cipher.Block, prefix []byte, resync OCFBResyncOption) cipher.Stream {
	blockSize := block.BlockSize()
	if len(prefix) != blockSize+2 {
		return nil
	}

	x := &ocfbDecrypter{
		b:       block,
		fre:     make([]byte, blockSize),
		outUsed: 0,
	}
	prefixCopy := make([]byte, len(prefix))
	copy(prefixCopy, prefix)

	block.Encrypt(x.fre, x.fre)
	for i := 0; i < blockSize; i++ {
		prefixCopy[i] ^= x.fre[i]
	}

	block.Encrypt(x.fre, prefix[:blockSize])
	prefixCopy[blockSize] ^= x.fre[0]
	prefixCopy[blockSize+1] ^= x.fre[1]

	if prefixCopy[blockSize-2] != prefixCopy[blockSize] ||
		prefixCopy[blockSize-1] != prefixCopy[blockSize+1] {
		return nil
	}

	if resync {
		block.Encrypt(x.fre, prefix[2:])
	} else {
		x.fre[0] = prefix[blockSize]
		x.fre[1] = prefix[blockSize+1]
		x.outUsed = 2
	}
	copy(prefix, prefixCopy)
	return x
}

func (x *ocfbDecrypter) XORKeyStream(dst, src []byte) {
	for i := 0; i < len(src); i++ {
		if x.outUsed == len(x.fre) {
			x.b.Encrypt(x.fre, x.fre)
			x.outUsed = 0
		}

		c := src[i]
		dst[i] = x.fre[x.outUsed] ^ src[i]
		x.fre[x.outUsed] = c
		x.outUsed++
	}
}