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/* Copyright 2018 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 javax.crypto.SecretKey;
/**
* Implementation of {@link D2DConnectionContext} for version 0 of the D2D protocol. In this
* version, communication is half-duplex, as there is a shared key and a shared sequence number
* between the two sides.
*/
public class D2DConnectionContextV0 extends D2DConnectionContext {
public static final int PROTOCOL_VERSION = 0;
private final SecretKey sharedKey;
private int sequenceNumber;
/**
* Package private constructor. Should never be called directly except by the
* {@link D2DHandshakeContext}
*
* @param sharedKey
* @param initialSequenceNumber
*/
D2DConnectionContextV0(SecretKey sharedKey, int initialSequenceNumber) {
super(PROTOCOL_VERSION);
this.sharedKey = sharedKey;
this.sequenceNumber = initialSequenceNumber;
}
@Override
public byte[] getSessionUnique() throws NoSuchAlgorithmException {
if (sharedKey == null) {
throw new IllegalStateException(
"Connection has not been correctly initialized; shared key is null");
}
MessageDigest md = MessageDigest.getInstance("SHA-256");
md.update(D2DCryptoOps.SALT);
return md.digest(sharedKey.getEncoded());
}
@Override
protected void incrementSequenceNumberForEncoding() {
sequenceNumber++;
}
@Override
protected void incrementSequenceNumberForDecoding() {
sequenceNumber++;
}
@Override
int getSequenceNumberForEncoding() {
return sequenceNumber;
}
@Override
int getSequenceNumberForDecoding() {
return sequenceNumber;
}
@Override
SecretKey getEncodeKey() {
return sharedKey;
}
@Override
SecretKey getDecodeKey() {
return sharedKey;
}
/**
* Structure of saved session is:
* +-----------------------------------------------------+
* | 1 Byte | 4 Bytes (big endian) | 32 Bytes |
* +-----------------------------------------------------+
* | Protocol Version | sequence number | key |
* +-----------------------------------------------------+
*/
@Override
public byte[] saveSession() {
ByteArrayOutputStream bytes = new ByteArrayOutputStream();
try {
// Protocol version
bytes.write(0);
// Sequence number
bytes.write(signedIntToBytes(sequenceNumber));
// Key
bytes.write(sharedKey.getEncoded());
} catch (IOException e) {
// should not happen
e.printStackTrace();
return null;
}
return bytes.toByteArray();
}
}
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