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blockcipher_aes_ctr.go
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blockcipher_aes_ctr.go
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/*
Copyright The ocicrypt 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 blockcipher
import (
"crypto/aes"
"crypto/cipher"
"crypto/hmac"
"crypto/rand"
"crypto/sha256"
"fmt"
"hash"
"io"
"github.com/containers/ocicrypt/utils"
"github.com/pkg/errors"
)
// AESCTRLayerBlockCipher implements the AES CTR stream cipher
type AESCTRLayerBlockCipher struct {
keylen int // in bytes
reader io.Reader
encrypt bool
stream cipher.Stream
err error
hmac hash.Hash
expHmac []byte
doneEncrypting bool
}
type aesctrcryptor struct {
bc *AESCTRLayerBlockCipher
}
// NewAESCTRLayerBlockCipher returns a new AES SIV block cipher of 256 or 512 bits
func NewAESCTRLayerBlockCipher(bits int) (LayerBlockCipher, error) {
if bits != 256 {
return nil, errors.New("AES CTR bit count not supported")
}
return &AESCTRLayerBlockCipher{keylen: bits / 8}, nil
}
func (r *aesctrcryptor) Read(p []byte) (int, error) {
var (
o int
)
if r.bc.err != nil {
return 0, r.bc.err
}
o, err := utils.FillBuffer(r.bc.reader, p)
if err != nil {
if err == io.EOF {
r.bc.err = err
} else {
return 0, err
}
}
if !r.bc.encrypt {
if _, err := r.bc.hmac.Write(p[:o]); err != nil {
r.bc.err = errors.Wrapf(err, "could not write to hmac")
return 0, r.bc.err
}
if r.bc.err == io.EOF {
// Before we return EOF we let the HMAC comparison
// provide a verdict
if !hmac.Equal(r.bc.hmac.Sum(nil), r.bc.expHmac) {
r.bc.err = fmt.Errorf("could not properly decrypt byte stream; exp hmac: '%x', actual hmac: '%s'", r.bc.expHmac, r.bc.hmac.Sum(nil))
return 0, r.bc.err
}
}
}
r.bc.stream.XORKeyStream(p[:o], p[:o])
if r.bc.encrypt {
if _, err := r.bc.hmac.Write(p[:o]); err != nil {
r.bc.err = errors.Wrapf(err, "could not write to hmac")
return 0, r.bc.err
}
if r.bc.err == io.EOF {
// Final data encrypted; Do the 'then-MAC' part
r.bc.doneEncrypting = true
}
}
return o, r.bc.err
}
// init initializes an instance
func (bc *AESCTRLayerBlockCipher) init(encrypt bool, reader io.Reader, opts LayerBlockCipherOptions) (LayerBlockCipherOptions, error) {
var (
err error
)
key := opts.Private.SymmetricKey
if len(key) != bc.keylen {
return LayerBlockCipherOptions{}, fmt.Errorf("invalid key length of %d bytes; need %d bytes", len(key), bc.keylen)
}
nonce, ok := opts.GetOpt("nonce")
if !ok {
nonce = make([]byte, aes.BlockSize)
if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
return LayerBlockCipherOptions{}, errors.Wrap(err, "unable to generate random nonce")
}
}
block, err := aes.NewCipher(key)
if err != nil {
return LayerBlockCipherOptions{}, errors.Wrap(err, "aes.NewCipher failed")
}
bc.reader = reader
bc.encrypt = encrypt
bc.stream = cipher.NewCTR(block, nonce)
bc.err = nil
bc.hmac = hmac.New(sha256.New, key)
bc.expHmac = opts.Public.Hmac
bc.doneEncrypting = false
if !encrypt && len(bc.expHmac) == 0 {
return LayerBlockCipherOptions{}, errors.New("HMAC is not provided for decryption process")
}
lbco := LayerBlockCipherOptions{
Private: PrivateLayerBlockCipherOptions{
SymmetricKey: key,
CipherOptions: map[string][]byte{
"nonce": nonce,
},
},
}
return lbco, nil
}
// GenerateKey creates a synmmetric key
func (bc *AESCTRLayerBlockCipher) GenerateKey() ([]byte, error) {
key := make([]byte, bc.keylen)
if _, err := io.ReadFull(rand.Reader, key); err != nil {
return nil, err
}
return key, nil
}
// Encrypt takes in layer data and returns the ciphertext and relevant LayerBlockCipherOptions
func (bc *AESCTRLayerBlockCipher) Encrypt(plainDataReader io.Reader, opt LayerBlockCipherOptions) (io.Reader, Finalizer, error) {
lbco, err := bc.init(true, plainDataReader, opt)
if err != nil {
return nil, nil, err
}
finalizer := func() (LayerBlockCipherOptions, error) {
if !bc.doneEncrypting {
return LayerBlockCipherOptions{}, errors.New("Read()ing not complete, unable to finalize")
}
if lbco.Public.CipherOptions == nil {
lbco.Public.CipherOptions = map[string][]byte{}
}
lbco.Public.Hmac = bc.hmac.Sum(nil)
return lbco, nil
}
return &aesctrcryptor{bc}, finalizer, nil
}
// Decrypt takes in layer ciphertext data and returns the plaintext and relevant LayerBlockCipherOptions
func (bc *AESCTRLayerBlockCipher) Decrypt(encDataReader io.Reader, opt LayerBlockCipherOptions) (io.Reader, LayerBlockCipherOptions, error) {
lbco, err := bc.init(false, encDataReader, opt)
if err != nil {
return nil, LayerBlockCipherOptions{}, err
}
return utils.NewDelayedReader(&aesctrcryptor{bc}, 1024*10), lbco, nil
}