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
|
// Copyright (C) 2019 ProtonTech AG
package packet
import "math/bits"
// CipherSuite contains a combination of Cipher and Mode
type CipherSuite struct {
// The cipher function
Cipher CipherFunction
// The AEAD mode of operation.
Mode AEADMode
}
// AEADConfig collects a number of AEAD parameters along with sensible defaults.
// A nil AEADConfig is valid and results in all default values.
type AEADConfig struct {
// The AEAD mode of operation.
DefaultMode AEADMode
// Amount of octets in each chunk of data
ChunkSize uint64
}
// Mode returns the AEAD mode of operation.
func (conf *AEADConfig) Mode() AEADMode {
// If no preference is specified, OCB is used (which is mandatory to implement).
if conf == nil || conf.DefaultMode == 0 {
return AEADModeOCB
}
mode := conf.DefaultMode
if mode != AEADModeEAX && mode != AEADModeOCB && mode != AEADModeGCM {
panic("AEAD mode unsupported")
}
return mode
}
// ChunkSizeByte returns the byte indicating the chunk size. The effective
// chunk size is computed with the formula uint64(1) << (chunkSizeByte + 6)
// limit to 16 = 4 MiB
// https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-07.html#section-5.13.2
func (conf *AEADConfig) ChunkSizeByte() byte {
if conf == nil || conf.ChunkSize == 0 {
return 12 // 1 << (12 + 6) == 262144 bytes
}
chunkSize := conf.ChunkSize
exponent := bits.Len64(chunkSize) - 1
switch {
case exponent < 6:
exponent = 6
case exponent > 16:
exponent = 16
}
return byte(exponent - 6)
}
// decodeAEADChunkSize returns the effective chunk size. In 32-bit systems, the
// maximum returned value is 1 << 30.
func decodeAEADChunkSize(c byte) int {
size := uint64(1 << (c + 6))
if size != uint64(int(size)) {
return 1 << 30
}
return int(size)
}
|
