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
|
// Package padding adds and removes padding for AES-CBC mode.
//
// Copyright (c) 2013 CloudFlare, Inc.
package padding
import "errors"
// The final byte of a padded []byte indicates the number of padding
// bytes that were added. The padding bytes are always NUL bytes and
// up to 16 bytes may be added.
//
// Examples:
//
// 1. Data to be padded has a length divisible by 16. 16 bytes will be
// added where the first 15 are 0x00 and the final byte is 0x10.
//
// 2. Data to be padded has a length with remainder 15 when divided by
// 16. One byte will be added and that byte will be 0x01 (indicating
// one byte of padding).
//
// 3. Data to be padded has a length with remainder 2 when divided by
// 16. 14 bytes will be added. The first 13 will be 0x00 and then final
// byte will be 0x0e.
//
// Removing padding is trivial: the number of bytes specified by the
// final byte are removed.
// RemovePadding removes padding from data that was added with
// AddPadding
func RemovePadding(b []byte) ([]byte, error) {
l := int(b[len(b)-1])
if l > 16 {
return nil, errors.New("Padding incorrect")
}
return b[:len(b)-l], nil
}
// AddPadding adds padding to a block of data
func AddPadding(b []byte) []byte {
l := 16 - len(b)%16
padding := make([]byte, l)
padding[l-1] = byte(l)
return append(b, padding...)
}
|
