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/*
*
* Copyright 2018 gRPC authors.
*
* Licensed 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 conn
import (
"crypto/cipher"
core "google.golang.org/grpc/credentials/alts/internal"
)
const (
// Overflow length n in bytes, never encrypt more than 2^(n*8) frames (in
// each direction).
overflowLenAES128GCMRekey = 8
nonceLen = 12
aeadKeyLen = 16
kdfKeyLen = 32
kdfCounterOffset = 2
kdfCounterLen = 6
sizeUint64 = 8
)
// aes128gcmRekey is the struct that holds necessary information for ALTS record.
// The counter value is NOT included in the payload during the encryption and
// decryption operations.
type aes128gcmRekey struct {
// inCounter is used in ALTS record to check that incoming counters are
// as expected, since ALTS record guarantees that messages are unwrapped
// in the same order that the peer wrapped them.
inCounter Counter
outCounter Counter
inAEAD cipher.AEAD
outAEAD cipher.AEAD
}
// NewAES128GCMRekey creates an instance that uses aes128gcm with rekeying
// for ALTS record. The key argument should be 44 bytes, the first 32 bytes
// are used as a key for HKDF-expand and the remainining 12 bytes are used
// as a random mask for the counter.
func NewAES128GCMRekey(side core.Side, key []byte) (ALTSRecordCrypto, error) {
inCounter := NewInCounter(side, overflowLenAES128GCMRekey)
outCounter := NewOutCounter(side, overflowLenAES128GCMRekey)
inAEAD, err := newRekeyAEAD(key)
if err != nil {
return nil, err
}
outAEAD, err := newRekeyAEAD(key)
if err != nil {
return nil, err
}
return &aes128gcmRekey{
inCounter,
outCounter,
inAEAD,
outAEAD,
}, nil
}
// Encrypt is the encryption function. dst can contain bytes at the beginning of
// the ciphertext that will not be encrypted but will be authenticated. If dst
// has enough capacity to hold these bytes, the ciphertext and the tag, no
// allocation and copy operations will be performed. dst and plaintext do not
// overlap.
func (s *aes128gcmRekey) Encrypt(dst, plaintext []byte) ([]byte, error) {
// If we need to allocate an output buffer, we want to include space for
// GCM tag to avoid forcing ALTS record to reallocate as well.
dlen := len(dst)
dst, out := SliceForAppend(dst, len(plaintext)+GcmTagSize)
seq, err := s.outCounter.Value()
if err != nil {
return nil, err
}
data := out[:len(plaintext)]
copy(data, plaintext) // data may alias plaintext
// Seal appends the ciphertext and the tag to its first argument and
// returns the updated slice. However, SliceForAppend above ensures that
// dst has enough capacity to avoid a reallocation and copy due to the
// append.
dst = s.outAEAD.Seal(dst[:dlen], seq, data, nil)
s.outCounter.Inc()
return dst, nil
}
func (s *aes128gcmRekey) EncryptionOverhead() int {
return GcmTagSize
}
func (s *aes128gcmRekey) Decrypt(dst, ciphertext []byte) ([]byte, error) {
seq, err := s.inCounter.Value()
if err != nil {
return nil, err
}
plaintext, err := s.inAEAD.Open(dst, seq, ciphertext, nil)
if err != nil {
return nil, ErrAuth
}
s.inCounter.Inc()
return plaintext, nil
}
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