src/main/java/org/whispersystems/libaxolotl/kdf/DerivedMessageSecrets.java


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/**
 * Copyright (C) 2014 Open Whisper Systems
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.whispersystems.libaxolotl.kdf;

import org.whispersystems.libaxolotl.util.ByteUtil;

import java.text.ParseException;

import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class DerivedMessageSecrets {

  public  static final int SIZE              = 80;
  private static final int CIPHER_KEY_LENGTH = 32;
  private static final int MAC_KEY_LENGTH    = 32;
  private static final int IV_LENGTH         = 16;

  private final SecretKeySpec   cipherKey;
  private final SecretKeySpec   macKey;
  private final IvParameterSpec iv;

  public DerivedMessageSecrets(byte[] okm) {
    try {
      byte[][] keys = ByteUtil.split(okm, CIPHER_KEY_LENGTH, MAC_KEY_LENGTH, IV_LENGTH);

      this.cipherKey = new SecretKeySpec(keys[0], "AES");
      this.macKey    = new SecretKeySpec(keys[1], "HmacSHA256");
      this.iv        = new IvParameterSpec(keys[2]);
    } catch (ParseException e) {
      throw new AssertionError(e);
    }
  }

  public SecretKeySpec getCipherKey() {
    return cipherKey;
  }

  public SecretKeySpec getMacKey() {
    return macKey;
  }

  public IvParameterSpec getIv() {
    return iv;
  }
}