mirror of
https://github.com/octoleo/restic.git
synced 2024-11-25 22:27:35 +00:00
372 lines
8.7 KiB
Go
372 lines
8.7 KiB
Go
package crypto
|
|
|
|
import (
|
|
"crypto/aes"
|
|
"crypto/cipher"
|
|
"crypto/rand"
|
|
"encoding/json"
|
|
"fmt"
|
|
|
|
"github.com/restic/restic/internal/errors"
|
|
|
|
"golang.org/x/crypto/poly1305"
|
|
)
|
|
|
|
const (
|
|
aesKeySize = 32 // for AES-256
|
|
macKeySizeK = 16 // for AES-128
|
|
macKeySizeR = 16 // for Poly1305
|
|
macKeySize = macKeySizeK + macKeySizeR // for Poly1305-AES128
|
|
ivSize = aes.BlockSize
|
|
|
|
macSize = poly1305.TagSize
|
|
|
|
// Extension is the number of bytes a plaintext is enlarged by encrypting it.
|
|
Extension = ivSize + macSize
|
|
)
|
|
|
|
var (
|
|
// ErrUnauthenticated is returned when ciphertext verification has failed.
|
|
ErrUnauthenticated = errors.New("ciphertext verification failed")
|
|
)
|
|
|
|
// Key holds encryption and message authentication keys for a repository. It is stored
|
|
// encrypted and authenticated as a JSON data structure in the Data field of the Key
|
|
// structure.
|
|
type Key struct {
|
|
MACKey `json:"mac"`
|
|
EncryptionKey `json:"encrypt"`
|
|
}
|
|
|
|
// EncryptionKey is key used for encryption
|
|
type EncryptionKey [32]byte
|
|
|
|
// MACKey is used to sign (authenticate) data.
|
|
type MACKey struct {
|
|
K [16]byte // for AES-128
|
|
R [16]byte // for Poly1305
|
|
|
|
masked bool // remember if the MAC key has already been masked
|
|
}
|
|
|
|
// mask for key, (cf. http://cr.yp.to/mac/poly1305-20050329.pdf)
|
|
var poly1305KeyMask = [16]byte{
|
|
0xff,
|
|
0xff,
|
|
0xff,
|
|
0x0f, // 3: top four bits zero
|
|
0xfc, // 4: bottom two bits zero
|
|
0xff,
|
|
0xff,
|
|
0x0f, // 7: top four bits zero
|
|
0xfc, // 8: bottom two bits zero
|
|
0xff,
|
|
0xff,
|
|
0x0f, // 11: top four bits zero
|
|
0xfc, // 12: bottom two bits zero
|
|
0xff,
|
|
0xff,
|
|
0x0f, // 15: top four bits zero
|
|
}
|
|
|
|
func poly1305MAC(msg []byte, nonce []byte, key *MACKey) []byte {
|
|
k := poly1305PrepareKey(nonce, key)
|
|
|
|
var out [16]byte
|
|
poly1305.Sum(&out, msg, &k)
|
|
|
|
return out[:]
|
|
}
|
|
|
|
// mask poly1305 key
|
|
func maskKey(k *MACKey) {
|
|
if k == nil || k.masked {
|
|
return
|
|
}
|
|
|
|
for i := 0; i < poly1305.TagSize; i++ {
|
|
k.R[i] = k.R[i] & poly1305KeyMask[i]
|
|
}
|
|
|
|
k.masked = true
|
|
}
|
|
|
|
// construct mac key from slice (k||r), with masking
|
|
func macKeyFromSlice(mk *MACKey, data []byte) {
|
|
copy(mk.K[:], data[:16])
|
|
copy(mk.R[:], data[16:32])
|
|
maskKey(mk)
|
|
}
|
|
|
|
// prepare key for low-level poly1305.Sum(): r||n
|
|
func poly1305PrepareKey(nonce []byte, key *MACKey) [32]byte {
|
|
var k [32]byte
|
|
|
|
maskKey(key)
|
|
|
|
cipher, err := aes.NewCipher(key.K[:])
|
|
if err != nil {
|
|
panic(err)
|
|
}
|
|
cipher.Encrypt(k[16:], nonce[:])
|
|
|
|
copy(k[:16], key.R[:])
|
|
|
|
return k
|
|
}
|
|
|
|
func poly1305Verify(msg []byte, nonce []byte, key *MACKey, mac []byte) bool {
|
|
k := poly1305PrepareKey(nonce, key)
|
|
|
|
var m [16]byte
|
|
copy(m[:], mac)
|
|
|
|
return poly1305.Verify(&m, msg, &k)
|
|
}
|
|
|
|
// NewRandomKey returns new encryption and message authentication keys.
|
|
func NewRandomKey() *Key {
|
|
k := &Key{}
|
|
|
|
n, err := rand.Read(k.EncryptionKey[:])
|
|
if n != aesKeySize || err != nil {
|
|
panic("unable to read enough random bytes for encryption key")
|
|
}
|
|
|
|
n, err = rand.Read(k.MACKey.K[:])
|
|
if n != macKeySizeK || err != nil {
|
|
panic("unable to read enough random bytes for MAC encryption key")
|
|
}
|
|
|
|
n, err = rand.Read(k.MACKey.R[:])
|
|
if n != macKeySizeR || err != nil {
|
|
panic("unable to read enough random bytes for MAC key")
|
|
}
|
|
|
|
maskKey(&k.MACKey)
|
|
return k
|
|
}
|
|
|
|
// NewRandomNonce returns a new random nonce. It panics on error so that the
|
|
// program is safely terminated.
|
|
func NewRandomNonce() []byte {
|
|
iv := make([]byte, ivSize)
|
|
n, err := rand.Read(iv)
|
|
if n != ivSize || err != nil {
|
|
panic("unable to read enough random bytes for iv")
|
|
}
|
|
return iv
|
|
}
|
|
|
|
type jsonMACKey struct {
|
|
K []byte `json:"k"`
|
|
R []byte `json:"r"`
|
|
}
|
|
|
|
// MarshalJSON converts the MACKey to JSON.
|
|
func (m *MACKey) MarshalJSON() ([]byte, error) {
|
|
return json.Marshal(jsonMACKey{K: m.K[:], R: m.R[:]})
|
|
}
|
|
|
|
// UnmarshalJSON fills the key m with data from the JSON representation.
|
|
func (m *MACKey) UnmarshalJSON(data []byte) error {
|
|
j := jsonMACKey{}
|
|
err := json.Unmarshal(data, &j)
|
|
if err != nil {
|
|
return errors.Wrap(err, "Unmarshal")
|
|
}
|
|
copy(m.K[:], j.K)
|
|
copy(m.R[:], j.R)
|
|
|
|
return nil
|
|
}
|
|
|
|
// Valid tests whether the key k is valid (i.e. not zero).
|
|
func (m *MACKey) Valid() bool {
|
|
nonzeroK := false
|
|
for i := 0; i < len(m.K); i++ {
|
|
if m.K[i] != 0 {
|
|
nonzeroK = true
|
|
}
|
|
}
|
|
|
|
if !nonzeroK {
|
|
return false
|
|
}
|
|
|
|
for i := 0; i < len(m.R); i++ {
|
|
if m.R[i] != 0 {
|
|
return true
|
|
}
|
|
}
|
|
|
|
return false
|
|
}
|
|
|
|
// MarshalJSON converts the EncryptionKey to JSON.
|
|
func (k *EncryptionKey) MarshalJSON() ([]byte, error) {
|
|
return json.Marshal(k[:])
|
|
}
|
|
|
|
// UnmarshalJSON fills the key k with data from the JSON representation.
|
|
func (k *EncryptionKey) UnmarshalJSON(data []byte) error {
|
|
d := make([]byte, aesKeySize)
|
|
err := json.Unmarshal(data, &d)
|
|
if err != nil {
|
|
return errors.Wrap(err, "Unmarshal")
|
|
}
|
|
copy(k[:], d)
|
|
|
|
return nil
|
|
}
|
|
|
|
// Valid tests whether the key k is valid (i.e. not zero).
|
|
func (k *EncryptionKey) Valid() bool {
|
|
for i := 0; i < len(k); i++ {
|
|
if k[i] != 0 {
|
|
return true
|
|
}
|
|
}
|
|
|
|
return false
|
|
}
|
|
|
|
// ErrInvalidCiphertext is returned when trying to encrypt into the slice that
|
|
// holds the plaintext.
|
|
var ErrInvalidCiphertext = errors.New("invalid ciphertext, same slice used for plaintext")
|
|
|
|
// validNonce checks that nonce is not all zero.
|
|
func validNonce(nonce []byte) bool {
|
|
var sum byte
|
|
for _, b := range nonce {
|
|
sum |= b
|
|
}
|
|
return sum > 0
|
|
}
|
|
|
|
// statically ensure that *Key implements crypto/cipher.AEAD
|
|
var _ cipher.AEAD = &Key{}
|
|
|
|
// NonceSize returns the size of the nonce that must be passed to Seal
|
|
// and Open.
|
|
func (k *Key) NonceSize() int {
|
|
return ivSize
|
|
}
|
|
|
|
// Overhead returns the maximum difference between the lengths of a
|
|
// plaintext and its ciphertext.
|
|
func (k *Key) Overhead() int {
|
|
return macSize
|
|
}
|
|
|
|
// sliceForAppend takes a slice and a requested number of bytes. It returns a
|
|
// slice with the contents of the given slice followed by that many bytes and a
|
|
// second slice that aliases into it and contains only the extra bytes. If the
|
|
// original slice has sufficient capacity then no allocation is performed.
|
|
//
|
|
// taken from the stdlib, crypto/aes/aes_gcm.go
|
|
func sliceForAppend(in []byte, n int) (head, tail []byte) {
|
|
if total := len(in) + n; cap(in) >= total {
|
|
head = in[:total]
|
|
} else {
|
|
head = make([]byte, total)
|
|
copy(head, in)
|
|
}
|
|
tail = head[len(in):]
|
|
return
|
|
}
|
|
|
|
// Seal encrypts and authenticates plaintext, authenticates the
|
|
// additional data and appends the result to dst, returning the updated
|
|
// slice. The nonce must be NonceSize() bytes long and unique for all
|
|
// time, for a given key.
|
|
//
|
|
// The plaintext and dst may alias exactly or not at all. To reuse
|
|
// plaintext's storage for the encrypted output, use plaintext[:0] as dst.
|
|
func (k *Key) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
|
|
if !k.Valid() {
|
|
panic("key is invalid")
|
|
}
|
|
|
|
if len(additionalData) > 0 {
|
|
panic("additional data is not supported")
|
|
}
|
|
|
|
if len(nonce) != ivSize {
|
|
panic("incorrect nonce length")
|
|
}
|
|
|
|
if !validNonce(nonce) {
|
|
panic("nonce is invalid")
|
|
}
|
|
|
|
ret, out := sliceForAppend(dst, len(plaintext)+k.Overhead())
|
|
|
|
c, err := aes.NewCipher(k.EncryptionKey[:])
|
|
if err != nil {
|
|
panic(fmt.Sprintf("unable to create cipher: %v", err))
|
|
}
|
|
e := cipher.NewCTR(c, nonce)
|
|
e.XORKeyStream(out, plaintext)
|
|
|
|
mac := poly1305MAC(out[:len(plaintext)], nonce, &k.MACKey)
|
|
copy(out[len(plaintext):], mac)
|
|
|
|
return ret
|
|
}
|
|
|
|
// Open decrypts and authenticates ciphertext, authenticates the
|
|
// additional data and, if successful, appends the resulting plaintext
|
|
// to dst, returning the updated slice. The nonce must be NonceSize()
|
|
// bytes long and both it and the additional data must match the
|
|
// value passed to Seal.
|
|
//
|
|
// The ciphertext and dst may alias exactly or not at all. To reuse
|
|
// ciphertext's storage for the decrypted output, use ciphertext[:0] as dst.
|
|
//
|
|
// Even if the function fails, the contents of dst, up to its capacity,
|
|
// may be overwritten.
|
|
func (k *Key) Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
|
|
if !k.Valid() {
|
|
return nil, errors.New("invalid key")
|
|
}
|
|
|
|
// check parameters
|
|
if len(nonce) != ivSize {
|
|
panic("incorrect nonce length")
|
|
}
|
|
|
|
if !validNonce(nonce) {
|
|
return nil, errors.New("nonce is invalid")
|
|
}
|
|
|
|
// check for plausible length
|
|
if len(ciphertext) < k.Overhead() {
|
|
return nil, errors.Errorf("trying to decrypt invalid data: ciphertext too small")
|
|
}
|
|
|
|
l := len(ciphertext) - macSize
|
|
ct, mac := ciphertext[:l], ciphertext[l:]
|
|
|
|
// verify mac
|
|
if !poly1305Verify(ct, nonce, &k.MACKey, mac) {
|
|
return nil, ErrUnauthenticated
|
|
}
|
|
|
|
ret, out := sliceForAppend(dst, len(ct))
|
|
|
|
c, err := aes.NewCipher(k.EncryptionKey[:])
|
|
if err != nil {
|
|
panic(fmt.Sprintf("unable to create cipher: %v", err))
|
|
}
|
|
e := cipher.NewCTR(c, nonce)
|
|
e.XORKeyStream(out, ct)
|
|
|
|
return ret, nil
|
|
}
|
|
|
|
// Valid tests if the key is valid.
|
|
func (k *Key) Valid() bool {
|
|
return k.EncryptionKey.Valid() && k.MACKey.Valid()
|
|
}
|