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key.go
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key.go
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package superdog
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"encoding/binary"
"errors"
"io"
)
type CipherBlockMode uint8
type Cipher uint8
const (
CFB CipherBlockMode = iota
CTR
OFB
GCM
)
const (
AES Cipher = iota
)
type Key struct {
Cipher Cipher
CipherBlockMode CipherBlockMode
block cipher.Block
ivlen int
Version uint64
}
func NewKey(version uint64, c Cipher, bm CipherBlockMode, key []byte) (*Key, error) {
k := &Key{
Cipher: c,
CipherBlockMode: bm,
Version: version,
}
switch c {
case AES:
var err error
k.block, err = aes.NewCipher(key)
if err != nil {
return k, err
}
}
k.ivlen = k.block.BlockSize()
if k.CipherBlockMode == GCM {
k.ivlen = 12
}
return k, nil
}
func (k *Key) Encrypt(dst, src []byte) ([]byte, error) {
if len(dst) != len(src)+8+k.ivlen {
dst = make([]byte, len(src)+8+k.ivlen)
}
// Place encryption KeyID at the beginning of cipher text
binary.PutUvarint(dst[:8], k.Version)
// Followed by the IV
iv := dst[8 : k.ivlen+8]
if _, err := io.ReadAtLeast(rand.Reader, iv, k.ivlen); err != nil {
return src, err
}
switch k.CipherBlockMode {
case CFB:
stream := cipher.NewCFBEncrypter(k.block, iv)
stream.XORKeyStream(dst[8+k.ivlen:], src)
case CTR:
stream := cipher.NewCTR(k.block, iv)
stream.XORKeyStream(dst[8+k.ivlen:], src)
case OFB:
stream := cipher.NewOFB(k.block, iv)
stream.XORKeyStream(dst[8+k.ivlen:], src)
case GCM:
aead, err := cipher.NewGCM(k.block)
if err != nil {
return dst, err
}
dst = aead.Seal(dst[:8+k.ivlen], iv, src, nil)
}
return dst, nil
}
func (k *Key) Decrypt(dst, src []byte) ([]byte, error) {
if len(src) == 0 {
return []byte{}, nil
}
if len(src) < k.block.BlockSize() {
return nil, errors.New("Insufficient length")
}
iv := src[:k.ivlen]
text := src[k.ivlen:]
switch k.CipherBlockMode {
case CFB:
stream := cipher.NewCFBDecrypter(k.block, iv)
dst = dst[:len(text)]
stream.XORKeyStream(dst, text)
case CTR:
stream := cipher.NewCTR(k.block, iv)
dst = dst[:len(text)]
stream.XORKeyStream(dst, text)
case OFB:
stream := cipher.NewOFB(k.block, iv)
dst = dst[:len(text)]
stream.XORKeyStream(dst, text)
case GCM:
aead, err := cipher.NewGCM(k.block)
if err != nil {
return dst, err
}
return aead.Open(dst[:0], iv, text, nil)
}
return dst, nil
}