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aes_gcm.go
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aes_gcm.go
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// Copyright 2015-present, Cyrill @ Schumacher.fm and the CoreStore contributors
//
// 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 observer
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"io"
"os"
"github.com/corestoreio/errors"
"github.com/corestoreio/pkg/config"
)
// AESGCMOptions sets the Key and Nonce from this struct or from environment
// variables.
type AESGCMOptions struct {
// The key argument should be the AES key, either 16, 24, or 32 bytes to
// select AES-128, AES-192, or AES-256. If empty, a random key will be
// generated and discarded once the service gets shut down.
Key string
// KeyEnvironmentVariableName defines the name of the environment variable
// which contains the key used for encryption and decryption.
KeyEnvironmentVariableName string
Nonce []byte // max 12 bytes
NonceEnvironmentVariableName string
}
const nonceLength = 12
type aesGCM struct {
o AESGCMOptions
aead cipher.AEAD
eventType uint8
}
// NewAESGCM creates a new observer which can encrypt or decrypt a value with
// the AES-GCM mode. Only two events are supported: config.EventOnBeforeSet for
// encryption and config.EventOnAfterGet for decryption. For security reasons
// this function cannot be accessed via JSON or protocol buffers.
func NewAESGCM(eventType uint8, eo *AESGCMOptions) (config.Observer, error) {
if eventType != config.EventOnBeforeSet && eventType != config.EventOnAfterGet {
return nil, errors.NotValid.Newf("[config/observer] Event type can only be: EventOnBeforeSet (encryption) or EventOnAfterGet (decryption)")
}
key := []byte(eo.Key)
if k, ok := os.LookupEnv(eo.KeyEnvironmentVariableName); ok && eo.KeyEnvironmentVariableName != "" && k != "" {
key = []byte(k)
}
if len(key) == 0 {
key = make([]byte, 32) // AES-256
if _, err := io.ReadFull(rand.Reader, key); err != nil {
return nil, errors.ReadFailed.New(err, "[config/observer] ReadFull failed")
}
eo.Key = string(key)
}
block, err := aes.NewCipher(key)
if err != nil {
return nil, errors.NotValid.New(err, "[config/observer] The encryption key has a wrong format.")
}
// Never use more than 2^32 = [12]byte random nonces with a given key
// because of the risk of a repeat.
nonce := eo.Nonce
if k, ok := os.LookupEnv(eo.NonceEnvironmentVariableName); ok && eo.NonceEnvironmentVariableName != "" && k != "" {
nonce = []byte(k)
}
if len(eo.Nonce) != nonceLength {
nonce = make([]byte, nonceLength)
if _, err2 := io.ReadFull(rand.Reader, nonce); err2 != nil {
return nil, errors.ReadFailed.New(err2, "[config/observer] ReadFull failed")
}
}
eo.Nonce = append(eo.Nonce[:0], nonce...)
aead, err := cipher.NewGCM(block)
if err != nil {
return nil, errors.Fatal.New(err, "[config/observer] cipher GCM failed")
}
enc := &aesGCM{
o: *eo,
aead: aead,
eventType: eventType,
}
return enc, nil
}
// MustNewAESGCM same as NewAESGCM but panics on error.
func MustNewAESGCM(eventType uint8, eo *AESGCMOptions) config.Observer {
enc, err := NewAESGCM(eventType, eo)
if err != nil {
panic(err)
}
return enc
}
func (v *aesGCM) Observe(p config.Path, rawData []byte, found bool) ([]byte, error) {
switch v.eventType {
case config.EventOnBeforeSet:
return v.aead.Seal(nil, v.o.Nonce, rawData, nil), nil
case config.EventOnAfterGet:
if !found {
return nil, nil
}
plaintext, err := v.aead.Open(nil, v.o.Nonce, rawData, nil)
if err != nil {
return nil, errors.Wrapf(err, "[config/observer] For Path %q", p.String())
}
return plaintext, nil
}
return nil, errors.Fatal.Newf("[config/observer] A programmer made an error")
}