/
aes.go
93 lines (74 loc) · 1.97 KB
/
aes.go
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
// (c) 2018 EPFL
// This code is licensed under MIT license (see LICENSE.txt for details)
package encryption
import (
"bytes"
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"io"
)
// aesKeySize designates the fixed 128-bit AES key size.
const aesKeySize = 16
// AES is the AES-CBC object handler.
type AES struct{}
// NewAES returns a fresh AES-CBC instance.
func NewAES() *AES {
return &AES{}
}
// Generate creates a fresh 16-byte AES-CBC symmetric key. If seed is nil
// crypto.rand is used as the random stream.
func (a AES) Generate(seed []byte) ([]byte, error) {
var reader io.Reader
if seed == nil {
reader = rand.Reader
} else {
reader = bytes.NewReader(seed)
}
k := make([]byte, aesKeySize)
if _, err := io.ReadFull(reader, k); err != nil {
return nil, err
}
return k, nil
}
// Encrypt invokes the AES-CBC encryption routine.
func (a AES) Encrypt(key, msg []byte) ([]byte, error) {
block, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
// The message has to be padded to be a multiple of the block size.
padded := pad(msg)
ct := make([]byte, aes.BlockSize+len(padded))
iv := ct[:aes.BlockSize]
if _, err := rand.Read(iv); err != nil {
return nil, err
}
cbc := cipher.NewCBCEncrypter(block, iv)
cbc.CryptBlocks(ct[aes.BlockSize:], padded)
return ct, nil
}
// Decrypt invokes the AES-CBC decryption routine.
func (a AES) Decrypt(key, ct []byte) ([]byte, error) {
block, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
iv := ct[:aes.BlockSize]
ct = ct[aes.BlockSize:]
cbc := cipher.NewCBCDecrypter(block, iv)
cbc.CryptBlocks(ct, ct)
return unpad(ct), nil
}
// pad a byte slice to a multiple of the AES block size.
func pad(src []byte) []byte {
padding := aes.BlockSize - len(src)%aes.BlockSize
padtext := bytes.Repeat([]byte{byte(padding)}, padding)
return append(src, padtext...)
}
// unpad a byte slice.
func unpad(src []byte) []byte {
length := len(src)
unpadding := int(src[length-1])
return src[:(length - unpadding)]
}