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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
//
// https://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 com.google.security.cryptauth.lib.securegcm;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
import javax.crypto.SecretKey;
/**
* Implementation of {@link D2DConnectionContext} for version 1 of the D2D protocol. In this
* version, communication is fully duplex, as separate keys and sequence nubmers are used for
* encoding and decoding.
*/
public class D2DConnectionContextV1 extends D2DConnectionContext {
public static final int PROTOCOL_VERSION = 1;
private final SecretKey encodeKey;
private final SecretKey decodeKey;
private int encodeSequenceNumber;
private int decodeSequenceNumber;
/**
* Package private constructor. Should never be called directly except by the
* {@link D2DHandshakeContext}
*
* @param encodeKey
* @param decodeKey
* @param initialEncodeSequenceNumber
* @param initialDecodeSequenceNumber
*/
D2DConnectionContextV1(
SecretKey encodeKey,
SecretKey decodeKey,
int initialEncodeSequenceNumber,
int initialDecodeSequenceNumber) {
super(PROTOCOL_VERSION);
this.encodeKey = encodeKey;
this.decodeKey = decodeKey;
this.encodeSequenceNumber = initialEncodeSequenceNumber;
this.decodeSequenceNumber = initialDecodeSequenceNumber;
}
@Override
public byte[] getSessionUnique() throws NoSuchAlgorithmException {
if (encodeKey == null || decodeKey == null) {
throw new IllegalStateException(
"Connection has not been correctly initialized; encode key or decode key is null");
}
// Ensure that the initator and responder keys are hashed in a deterministic order, so they have
// the same session unique code.
byte[] encodeKeyBytes = encodeKey.getEncoded();
byte[] decodeKeyBytes = decodeKey.getEncoded();
int encodeKeyHash = Arrays.hashCode(encodeKeyBytes);
int decodeKeyHash = Arrays.hashCode(decodeKeyBytes);
byte[] firstKeyBytes = encodeKeyHash < decodeKeyHash ? encodeKeyBytes : decodeKeyBytes;
byte[] secondKeyBytes = firstKeyBytes == encodeKeyBytes ? decodeKeyBytes : encodeKeyBytes;
MessageDigest md = MessageDigest.getInstance("SHA-256");
md.update(D2DCryptoOps.SALT);
md.update(firstKeyBytes);
md.update(secondKeyBytes);
return md.digest();
}
@Override
protected void incrementSequenceNumberForEncoding() {
encodeSequenceNumber++;
}
@Override
protected void incrementSequenceNumberForDecoding() {
decodeSequenceNumber++;
}
@Override
int getSequenceNumberForEncoding() {
return encodeSequenceNumber;
}
@Override
int getSequenceNumberForDecoding() {
return decodeSequenceNumber;
}
@Override
SecretKey getEncodeKey() {
return encodeKey;
}
@Override
SecretKey getDecodeKey() {
return decodeKey;
}
/**
* Structure of saved session is:
* +------------------------------------------------------------------------------------------+
* | 1 Byte | 4 Bytes (big endian) | 4 Bytes (big endian) | 32 Bytes | 32 Bytes |
* +------------------------------------------------------------------------------------------+
* | Protocol Version | encode seq number | decode seq number | encode key | decode key |
* +------------------------------------------------------------------------------------------+
*/
@Override
public byte[] saveSession() {
ByteArrayOutputStream bytes = new ByteArrayOutputStream();
try {
// Protocol version
bytes.write(1);
// Encode sequence number
bytes.write(signedIntToBytes(encodeSequenceNumber));
// Decode sequence number
bytes.write(signedIntToBytes(decodeSequenceNumber));
// Encode Key
bytes.write(encodeKey.getEncoded());
// Decode Key
bytes.write(decodeKey.getEncoded());
} catch (IOException e) {
// should not happen
e.printStackTrace();
return null;
}
return bytes.toByteArray();
}
}
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