1// Copyright 2020 Google LLC 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// http://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14// 15//////////////////////////////////////////////////////////////////////////////// 16 17package subtle 18 19import "github.com/google/tink/go/subtle" 20 21// KEMKey represents a KEM managed key. 22type KEMKey struct { 23 Kem, SymmetricKey []byte 24} 25 26// ECIESHKDFSenderKem represents HKDF-based ECIES-KEM (key encapsulation mechanism) 27// for ECIES sender. 28type ECIESHKDFSenderKem struct { 29 recipientPublicKey *ECPublicKey 30} 31 32// encapsulate generates an HKDF-based KEMKey. 33func (s *ECIESHKDFSenderKem) encapsulate(hashAlg string, salt []byte, info []byte, keySize uint32, pointFormat string) (*KEMKey, error) { 34 35 pvt, err := GenerateECDHKeyPair(s.recipientPublicKey.Curve) 36 if err != nil { 37 return nil, err 38 } 39 pub := pvt.PublicKey 40 secret, err := ComputeSharedSecret(&s.recipientPublicKey.Point, pvt) 41 if err != nil { 42 return nil, err 43 } 44 45 sdata, err := PointEncode(pub.Curve, pointFormat, pub.Point) 46 if err != nil { 47 return nil, err 48 } 49 i := make([]byte, 0, len(sdata)+len(secret)) 50 i = append(i, sdata...) 51 i = append(i, secret...) 52 53 sKey, err := subtle.ComputeHKDF(hashAlg, i, salt, info, keySize) 54 if err != nil { 55 return nil, err 56 } 57 58 return &KEMKey{ 59 Kem: sdata, 60 SymmetricKey: sKey, 61 }, nil 62 63} 64