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JSch is a pure Java implementation of SSH2
There is a newer version: 0.2.21
/*
 * Copyright (c) 2012-2018 ymnk, JCraft,Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted
 * provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this list of conditions
 * and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
 * conditions and the following disclaimer in the documentation and/or other materials provided with
 * the distribution.
 *
 * 3. The names of the authors may not be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL JCRAFT, INC. OR ANY CONTRIBUTORS TO THIS SOFTWARE BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.jcraft.jsch.jce;

import com.jcraft.jsch.JSch;
import com.jcraft.jsch.Logger;
import com.jcraft.jsch.MAC;
import javax.crypto.Mac;
import javax.crypto.ShortBufferException;
import javax.crypto.spec.SecretKeySpec;

abstract class HMAC implements MAC {
  protected String name;
  protected int bsize;
  protected String algorithm;
  protected boolean etm;
  private Mac mac;

  @Override
  public int getBlockSize() {
    return bsize;
  };

  @Override
  public void init(byte[] key) throws Exception {
    if (key.length > bsize) {
      byte[] tmp = new byte[bsize];
      System.arraycopy(key, 0, tmp, 0, bsize);
      key = tmp;
    }
    SecretKeySpec skey = new SecretKeySpec(key, algorithm);
    mac = Mac.getInstance(algorithm);
    mac.init(skey);
  }

  private final byte[] tmp = new byte[4];

  @Override
  public void update(int i) {
    tmp[0] = (byte) (i >>> 24);
    tmp[1] = (byte) (i >>> 16);
    tmp[2] = (byte) (i >>> 8);
    tmp[3] = (byte) i;
    update(tmp, 0, 4);
  }

  @Override
  public void update(byte foo[], int s, int l) {
    mac.update(foo, s, l);
  }

  @Override
  public void doFinal(byte[] buf, int offset) {
    try {
      mac.doFinal(buf, offset);
    } catch (ShortBufferException e) {
      if (JSch.getLogger().isEnabled(Logger.ERROR)) {
        JSch.getLogger().log(Logger.ERROR, e.getMessage(), e);
      }
    }
  }

  @Override
  public String getName() {
    return name;
  }

  @Override
  public boolean isEtM() {
    return etm;
  }
}