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// Copyright 2020 Google LLC
//
// 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 subtle
import (
"bytes"
"errors"
"github.com/tink-crypto/tink-go/v2/tink"
)
// ECIESAEADHKDFHybridEncrypt is an instance of ECIES encryption with HKDF-KEM (key encapsulation mechanism)
// and AEAD-DEM (data encapsulation mechanism).
type ECIESAEADHKDFHybridEncrypt struct {
publicKey *ECPublicKey
hkdfSalt []byte
hkdfHMACAlgo string
pointFormat string
demHelper EciesAEADHKDFDEMHelper
}
// NewECIESAEADHKDFHybridEncrypt returns ECIES encryption construct with HKDF-KEM (key encapsulation mechanism)
// and AEAD-DEM (data encapsulation mechanism).
func NewECIESAEADHKDFHybridEncrypt(pub *ECPublicKey, hkdfSalt []byte, hkdfHMACAlgo string, ptFormat string, demHelper EciesAEADHKDFDEMHelper) (*ECIESAEADHKDFHybridEncrypt, error) {
c, err := GetCurve(pub.Curve.Params().Name)
if err != nil {
return nil, err
}
return &ECIESAEADHKDFHybridEncrypt{
publicKey: &ECPublicKey{
Curve: c,
Point: pub.Point,
},
hkdfSalt: hkdfSalt,
hkdfHMACAlgo: hkdfHMACAlgo,
pointFormat: ptFormat,
demHelper: demHelper,
}, nil
}
// Encrypt is used to encrypt using ECIES with a HKDF-KEM and AEAD-DEM mechanisms.
func (e *ECIESAEADHKDFHybridEncrypt) Encrypt(plaintext, contextInfo []byte) ([]byte, error) {
var b bytes.Buffer
sKem := &ECIESHKDFSenderKem{
recipientPublicKey: e.publicKey,
}
kemKey, err := sKem.encapsulate(e.hkdfHMACAlgo, e.hkdfSalt, contextInfo, e.demHelper.GetSymmetricKeySize(), e.pointFormat)
if err != nil {
return nil, err
}
prim, err := e.demHelper.GetAEADOrDAEAD(kemKey.SymmetricKey)
if err != nil {
return nil, err
}
var ct []byte
switch a := prim.(type) {
case tink.AEAD:
ct, err = a.Encrypt(plaintext, []byte{})
case tink.DeterministicAEAD:
ct, err = a.EncryptDeterministically(plaintext, []byte{})
default:
err = errors.New("Internal error: unexpected primitive type")
}
if err != nil {
return nil, err
}
b.Write(kemKey.Kem)
b.Write(ct)
return b.Bytes(), nil
}
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