| // 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 hybrid |
| |
| import ( |
| "errors" |
| |
| "github.com/google/tink/go/tink" |
| ) |
| |
| // ECIESAEADHKDFHybridDecrypt is an instance of ECIES decryption with HKDF-KEM (key encapsulation mechanism) |
| // and AEAD-DEM (data encapsulation mechanism). |
| type ECIESAEADHKDFHybridDecrypt struct { |
| privateKey *ECPrivateKey |
| hkdfSalt []byte |
| hkdfHMACAlgo string |
| pointFormat string |
| demHelper EciesAEADHKDFDEMHelper |
| } |
| |
| var _ tink.HybridDecrypt = (*ECIESAEADHKDFHybridDecrypt)(nil) |
| |
| // NewECIESAEADHKDFHybridDecrypt returns ECIES decryption construct with HKDF-KEM (key encapsulation mechanism) |
| // and AEAD-DEM (data encapsulation mechanism). |
| func NewECIESAEADHKDFHybridDecrypt(pvt *ECPrivateKey, hkdfSalt []byte, hkdfHMACAlgo string, ptFormat string, demHelper EciesAEADHKDFDEMHelper) (*ECIESAEADHKDFHybridDecrypt, error) { |
| return &ECIESAEADHKDFHybridDecrypt{ |
| privateKey: pvt, |
| hkdfSalt: hkdfSalt, |
| hkdfHMACAlgo: hkdfHMACAlgo, |
| pointFormat: ptFormat, |
| demHelper: demHelper, |
| }, nil |
| } |
| |
| // Decrypt is used to decrypt using ECIES with a HKDF-KEM and AEAD-DEM mechanisms. |
| func (e *ECIESAEADHKDFHybridDecrypt) Decrypt(ciphertext, contextInfo []byte) ([]byte, error) { |
| curve := e.privateKey.PublicKey.Curve |
| headerSize, err := encodingSizeInBytes(curve, e.pointFormat) |
| if err != nil { |
| return nil, err |
| } |
| if len(ciphertext) < headerSize { |
| return nil, errors.New("ciphertext too short") |
| } |
| var kemBytes = make([]byte, headerSize) |
| var ct = make([]byte, len(ciphertext)-headerSize) |
| copy(kemBytes, ciphertext[:headerSize]) |
| copy(ct, ciphertext[headerSize:]) |
| rKem := &ECIESHKDFRecipientKem{ |
| recipientPrivateKey: e.privateKey, |
| } |
| symmetricKey, err := rKem.decapsulate(kemBytes, e.hkdfHMACAlgo, e.hkdfSalt, contextInfo, e.demHelper.GetSymmetricKeySize(), e.pointFormat) |
| if err != nil { |
| return nil, err |
| } |
| aead, err := e.demHelper.GetAEAD(symmetricKey) |
| if err != nil { |
| return nil, err |
| } |
| return aead.Decrypt(ct, []byte{}) |
| } |