Documentation
¶
Overview ¶
Package padding provides functions for padding blocks of plain text in the context of block cipher mode of encryption like ECB or CBC.
Index ¶
Examples ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
This section is empty.
Types ¶
type Padder ¶
type Padder struct {
// contains filtered or unexported fields
}
Padder struct embeds attributes necessary for the padding calculation (e.g. block size). It implements the Padding interface.
func (*Padder) Pad ¶
Pad returns the byte array passed as a parameter padded with bytes such that the new byte array will be an exact multiple of the expected block size. For example, if the expected block size is 8 bytes (e.g. PKCS #5) and that the initial byte array is:
[]byte{0x0A, 0x0B, 0x0C, 0x0D}
the returned array will be:
[]byte{0x0A, 0x0B, 0x0C, 0x0D, 0x04, 0x04, 0x04, 0x04}
The value of each octet of the padding is the size of the padding. If the array passed as a parameter is already an exact multiple of the block size, the original array will be padded with a full block.
Example ¶
p := []byte{0x0A, 0x0B, 0x0C, 0x0D}
fmt.Printf("%X\n", p)
padder := NewPkcs5Padding()
p, err := padder.Pad(p)
if err != nil {
panic(err.Error())
}
fmt.Printf("%X\n", p)
Output: 0A0B0C0D 0A0B0C0D04040404
Example (Second) ¶
p := []byte{0x0A, 0x0B, 0x0C, 0x0D, 0x0A, 0x0B, 0x0C, 0x0D}
fmt.Printf("%X\n", p)
padder := NewPkcs5Padding()
p, err := padder.Pad(p)
if err != nil {
panic(err.Error())
}
fmt.Printf("%X\n", p)
Output: 0A0B0C0D0A0B0C0D 0A0B0C0D0A0B0C0D0808080808080808
Example (Third) ¶
p := []byte{0x0A, 0x0B, 0x0C, 0x0D}
fmt.Printf("%X\n", p)
padder := NewPkcs7Padding(16) // 16-byte block size
p, err := padder.Pad(p)
if err != nil {
panic(err.Error())
}
fmt.Printf("%X\n", p)
Output: 0A0B0C0D 0A0B0C0D0C0C0C0C0C0C0C0C0C0C0C0C
func (*Padder) Unpad ¶
Unpad removes the padding of a given byte array, according to the same rules as described in the Pad function. For example if the byte array passed as a parameter is:
[]byte{0x0A, 0x0B, 0x0C, 0x0D, 0x04, 0x04, 0x04, 0x04}
the returned array will be:
[]byte{0x0A, 0x0B, 0x0C, 0x0D}
Example ¶
p := []byte{0x0A, 0x0B, 0x0C, 0x0D, 0x04, 0x04, 0x04, 0x04}
fmt.Printf("%X\n", p)
padder := NewPkcs5Padding()
p, err := padder.Unpad(p)
if err != nil {
panic(err.Error())
}
fmt.Printf("%X\n", p)
Output: 0A0B0C0D04040404 0A0B0C0D
Example (Empty) ¶
p := []byte{0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08}
fmt.Printf("%X\n", p)
padder := NewPkcs7Padding(8) // 8-byte block size
p, err := padder.Unpad(p)
if err != nil {
panic(err.Error())
}
fmt.Printf("%v\n", p)
Output: 0808080808080808 []
Example (Lastzero) ¶
p := []byte{0x0A, 0x0B, 0x0C, 0x0D, 0x04, 0x04, 0x04, 0x00}
fmt.Printf("%X\n", p)
padder := NewPkcs5Padding()
p, err := padder.Unpad(p)
if err != nil {
fmt.Println(err)
} else {
fmt.Printf("%X\n", p)
}
Output: 0A0B0C0D04040400 crypto/padding: invalid last byte of padding
Example (Second) ¶
p := []byte{0x0A, 0x0B, 0x0C, 0x0D, 0x0A, 0x0B, 0x0C, 0x0D,
0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08, 0x08}
fmt.Printf("%X\n", p)
padder := NewPkcs5Padding()
p, err := padder.Unpad(p)
if err != nil {
panic(err.Error())
}
fmt.Printf("%X\n", p)
Output: 0A0B0C0D0A0B0C0D0808080808080808 0A0B0C0D0A0B0C0D
Example (Third) ¶
p := []byte{0x0A, 0x0B, 0x0C, 0x0D, 0x0C, 0x0C, 0x0C, 0x0C,
0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C}
fmt.Printf("%X\n", p)
padder := NewPkcs7Padding(16) // 16-byte block size
p, err := padder.Unpad(p)
if err != nil {
panic(err.Error())
}
fmt.Printf("%X\n", p)
Output: 0A0B0C0D0C0C0C0C0C0C0C0C0C0C0C0C 0A0B0C0D
type Padding ¶
Padding interface defines functions Pad and Unpad implemented for PKCS #5 and PKCS #7 types of padding.
func NewPkcs5Padding ¶
func NewPkcs5Padding() Padding
NewPkcs5Padding returns a PKCS5 padding type structure. The blocksize defaults to 8 bytes (64-bit). See https://tools.ietf.org/html/rfc2898 PKCS #5: Password-Based Cryptography. Specification Version 2.0
func NewPkcs7Padding ¶
NewPkcs7Padding returns a PKCS7 padding type structure. The blocksize is passed as a parameter. See https://tools.ietf.org/html/rfc2315 PKCS #7: Cryptographic Message Syntax Version 1.5. For example the block size for AES is 16 bytes (128 bits).
Source Files