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encrypt.go
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encrypt.go
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/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package sec
import (
"bytes"
"crypto/aes"
"crypto/cipher"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/hmac"
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/base64"
"golang.org/x/crypto/hkdf"
"io"
keywrap "github.com/NickBall/go-aes-key-wrap"
"github.com/apache/mynewt-artifact/errors"
)
type EncType int
const (
ENC_TYPE_AES_128 EncType = iota
ENC_TYPE_AES_256
ENC_TYPE_RSA_2048
)
// XXX: Only RSA supported for now.
type PrivEncKey struct {
Rsa *rsa.PrivateKey
}
type PubEncKey struct {
Rsa *rsa.PublicKey
Ec *ecdsa.PublicKey
Aes cipher.Block
}
var encTypeNameMap = map[EncType]string{
ENC_TYPE_AES_128: "aes128",
ENC_TYPE_AES_256: "aes256",
ENC_TYPE_RSA_2048: "rsa2048",
}
func EncTypeString(typ EncType) string {
s := encTypeNameMap[typ]
if s == "" {
return "unknown"
} else {
return s
}
}
func EncStringType(s string) (EncType, error) {
for k, v := range encTypeNameMap {
if s == v {
return k, nil
}
}
return 0, errors.Errorf("unknown enc type name: \"%s\"", s)
}
func parsePubKePem(b []byte) (PubEncKey, error) {
key := PubEncKey{}
itf, err := parsePubPemKey(b)
if err != nil {
return key, err
}
switch pub := itf.(type) {
case *rsa.PublicKey:
key.Rsa = pub
case *ecdsa.PublicKey:
key.Ec = pub
default:
return key, errors.Errorf(
"unknown public encryption key type: %T", pub)
}
return key, nil
}
func parsePubKeBase64(keyBytes []byte) (PubEncKey, error) {
if len(keyBytes) != 16 && len(keyBytes) != 32 {
return PubEncKey{}, errors.Errorf(
"unexpected key size: %d != 16 or 32", len(keyBytes))
}
cipher, err := aes.NewCipher(keyBytes)
if err != nil {
return PubEncKey{}, errors.Wrapf(err,
"error creating keywrap cipher")
}
return PubEncKey{
Aes: cipher,
}, nil
}
func ParsePubEncKey(keyBytes []byte) (PubEncKey, error) {
b, err := base64.StdEncoding.DecodeString(string(keyBytes))
if err == nil {
return parsePubKeBase64(b)
}
// Not base64-encoded; assume it is PEM.
return parsePubKePem(keyBytes)
}
func (key *PrivEncKey) PubEncKey() PubEncKey {
return PubEncKey{
Rsa: key.Rsa.Public().(*rsa.PublicKey),
}
}
func (key *PubEncKey) AssertValid() {
if key.Rsa == nil && key.Aes == nil && key.Ec == nil {
panic("invalid public encryption key; neither RSA nor AES nor EC-P256")
}
}
func (key *PubEncKey) EncType() (EncType, error) {
if key.Rsa != nil {
return ENC_TYPE_RSA_2048, nil
} else if key.Aes != nil {
switch key.Aes.BlockSize() {
case 128 / 8:
return ENC_TYPE_AES_128, nil
case 256 / 8:
return ENC_TYPE_AES_256, nil
default:
return 0, errors.Errorf("illegal AES key block size: %d", key.Aes.BlockSize())
}
} else {
return 0, errors.Errorf("invalid enc key: all members nil")
}
}
func encryptRsa(pubk *rsa.PublicKey, plainSecret []byte) ([]byte, error) {
rng := rand.Reader
cipherSecret, err := rsa.EncryptOAEP(
sha256.New(), rng, pubk, plainSecret, nil)
if err != nil {
return nil, errors.Wrapf(err, "Error from encryption")
}
return cipherSecret, nil
}
func encryptEc256(peerPubK *ecdsa.PublicKey, plainSecret []byte) ([]byte, error) {
pk, x, y, err := elliptic.GenerateKey(elliptic.P256(), rand.Reader)
if err != nil {
return nil, errors.Wrapf(err, "Could not generate ephemeral EC keypair")
}
pubk := elliptic.Marshal(elliptic.P256(), x, y)
shared, _ := elliptic.P256().ScalarMult(peerPubK.X, peerPubK.Y, pk)
kdf := hkdf.New(sha256.New, shared.Bytes(), nil, []byte("MCUBoot_ECIES_v1"))
derived := make([]byte, 48)
_, err = kdf.Read(derived)
if err != nil {
return nil, errors.Wrapf(err, "Error during key derivation")
}
cipherSecret, err := EncryptAES(plainSecret, derived[:16], nil)
if err != nil {
return nil, errors.Wrapf(err, "Error encrypting key")
}
h := hmac.New(sha256.New, derived[16:])
h.Write(cipherSecret)
mac := h.Sum(nil)
var tlv []byte
tlv = append(tlv, pubk...)
tlv = append(tlv, mac...)
tlv = append(tlv, cipherSecret...)
return tlv, nil
}
func encryptAes(c cipher.Block, plain []byte) ([]byte, error) {
ciph, err := keywrap.Wrap(c, plain)
if err != nil {
return nil, errors.Wrapf(err, "error key-wrapping")
}
return ciph, nil
}
func (k *PubEncKey) Encrypt(plain []byte) ([]byte, error) {
k.AssertValid()
if k.Rsa != nil {
return encryptRsa(k.Rsa, plain)
} else if k.Ec != nil {
return encryptEc256(k.Ec, plain)
} else {
return encryptAes(k.Aes, plain)
}
}
func ParsePrivEncKey(keyBytes []byte) (PrivEncKey, error) {
rpk, err := x509.ParsePKCS1PrivateKey(keyBytes)
if err != nil {
return PrivEncKey{}, errors.Wrapf(err, "error parsing private key file")
}
return PrivEncKey{
Rsa: rpk,
}, nil
}
func decryptRsa(privk *rsa.PrivateKey, ciph []byte) ([]byte, error) {
rng := rand.Reader
plain, err := rsa.DecryptOAEP(sha256.New(), rng, privk, ciph, nil)
if err != nil {
return nil, errors.Wrapf(err, "error from encryption")
}
return plain, nil
}
func (k *PrivEncKey) Decrypt(ciph []byte) ([]byte, error) {
return decryptRsa(k.Rsa, ciph)
}
func EncryptAES(plain []byte, secret []byte, nonce []byte) ([]byte, error) {
blk, err := aes.NewCipher(secret)
if err != nil {
return nil, errors.Errorf("Failed to create block cipher")
}
var iv []byte
if nonce == nil {
iv = make([]byte, 16)
} else {
zeros := make([]byte, 8)
iv = append(nonce, zeros...)
}
stream := cipher.NewCTR(blk, iv)
dataBuf := make([]byte, 16)
encBuf := make([]byte, 16)
r := bytes.NewReader(plain)
w := bytes.Buffer{}
for {
cnt, err := r.Read(dataBuf)
if err != nil && err != io.EOF {
return nil, errors.Wrapf(err, "Failed to read from plaintext")
}
if cnt == 0 {
break
}
stream.XORKeyStream(encBuf, dataBuf[0:cnt])
if _, err = w.Write(encBuf[0:cnt]); err != nil {
return nil, errors.Wrapf(err, "failed to write ciphertext")
}
}
return w.Bytes(), nil
}