1 // Copyright 2017 Google Inc. 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 17 package com.google.crypto.tink.subtle; 18 19 import java.security.GeneralSecurityException; 20 import java.security.interfaces.ECPrivateKey; 21 import java.security.interfaces.ECPublicKey; 22 23 /** 24 * HKDF-based KEM (key encapsulation mechanism) for ECIES recipient. 25 * 26 * @since 1.0.0 27 */ 28 public final class EciesHkdfRecipientKem { 29 private ECPrivateKey recipientPrivateKey; 30 EciesHkdfRecipientKem(final ECPrivateKey recipientPrivateKey)31 public EciesHkdfRecipientKem(final ECPrivateKey recipientPrivateKey) { 32 this.recipientPrivateKey = recipientPrivateKey; 33 } 34 generateKey( byte[] kemBytes, String hmacAlgo, final byte[] hkdfSalt, final byte[] hkdfInfo, int keySizeInBytes, EllipticCurves.PointFormatType pointFormat)35 public byte[] generateKey( 36 byte[] kemBytes, 37 String hmacAlgo, 38 final byte[] hkdfSalt, 39 final byte[] hkdfInfo, 40 int keySizeInBytes, 41 EllipticCurves.PointFormatType pointFormat) 42 throws GeneralSecurityException { 43 ECPublicKey ephemeralPublicKey = EllipticCurves.getEcPublicKey( 44 recipientPrivateKey.getParams(), pointFormat, kemBytes); 45 byte[] sharedSecret = EllipticCurves.computeSharedSecret( 46 recipientPrivateKey, ephemeralPublicKey); 47 return Hkdf.computeEciesHkdfSymmetricKey( 48 kemBytes, sharedSecret, hmacAlgo, hkdfSalt, hkdfInfo, keySizeInBytes); 49 } 50 } 51