package com.google.crypto.tink.subtle;
import java.security.GeneralSecurityException;
import java.security.KeyPair;
import java.security.interfaces.ECPrivateKey;
import java.security.interfaces.ECPublicKey;
public final class EciesHkdfSenderKem {
private ECPublicKey recipientPublicKey;
public static final class KemKey {
private final ImmutableByteArray kemBytes;
private final ImmutableByteArray symmetricKey;
public KemKey(final byte[] kemBytes, final byte[] symmetricKey) {
this.kemBytes = ImmutableByteArray.of(kemBytes);
this.symmetricKey = ImmutableByteArray.of(symmetricKey);
}
public byte[] getKemBytes() {
if (kemBytes == null) {
return null;
} else {
return kemBytes.getBytes();
}
}
public byte[] getSymmetricKey() {
if (symmetricKey == null) {
return null;
} else {
return symmetricKey.getBytes();
}
}
}
public EciesHkdfSenderKem(final ECPublicKey recipientPublicKey) {
this.recipientPublicKey = recipientPublicKey;
}
public KemKey generateKey(
String hmacAlgo,
final byte[] hkdfSalt,
final byte[] hkdfInfo,
int keySizeInBytes,
EllipticCurves.PointFormatType pointFormat)
throws GeneralSecurityException {
KeyPair ephemeralKeyPair = EllipticCurves.generateKeyPair(recipientPublicKey.getParams());
ECPublicKey ephemeralPublicKey = (ECPublicKey) ephemeralKeyPair.getPublic();
ECPrivateKey ephemeralPrivateKey = (ECPrivateKey) ephemeralKeyPair.getPrivate();
byte[] sharedSecret = EllipticCurves.computeSharedSecret(
ephemeralPrivateKey, recipientPublicKey);
byte[] kemBytes =
EllipticCurves.pointEncode(
ephemeralPublicKey.getParams().getCurve(), pointFormat, ephemeralPublicKey.getW());
byte[] symmetricKey =
Hkdf.computeEciesHkdfSymmetricKey(
kemBytes, sharedSecret, hmacAlgo, hkdfSalt, hkdfInfo, keySizeInBytes);
return new KemKey(kemBytes, symmetricKey);
}
}