@Override
  public synchronized int read(byte[] b, int off, int len) throws IOException {
    if (len == 1) {
      int c = read();
      if (c == -1) {
        return -1;
      }

      b[off] = (byte) c;
      return 1;
    }

    if (buffer.available() == 0) {
      int nb = this.in.read(b, off, len);
      if (nb == -1) {
        return nb;
      }
      buffer.putRawBytes(b, off, nb);
    }

    int nb = 0;
    for (int curPos = off; (nb < len) && (buffer.available() > 0); nb++, curPos++) {
      b[curPos] = (byte) read();
    }

    return nb;
  }
  @Override
  public Boolean doAuth(Buffer buffer, boolean init) throws Exception {
    ValidateUtils.checkTrue(init, "Instance not initialized");
    boolean hasSig = buffer.getBoolean();
    String alg = buffer.getString();

    int oldLim = buffer.wpos();
    int oldPos = buffer.rpos();
    int len = buffer.getInt();
    buffer.wpos(buffer.rpos() + len);
    PublicKey key = buffer.getRawPublicKey();
    ServerFactoryManager manager = session.getFactoryManager();
    Signature verif =
        ValidateUtils.checkNotNull(
            NamedFactory.Utils.create(manager.getSignatureFactories(), alg),
            "No verifier located for algorithm=%s",
            alg);
    verif.initVerifier(key);
    buffer.wpos(oldLim);

    byte[] sig = hasSig ? buffer.getBytes() : null;

    PublickeyAuthenticator authenticator =
        ValidateUtils.checkNotNull(
            manager.getPublickeyAuthenticator(), "No PublickeyAuthenticator configured");
    if (!authenticator.authenticate(username, key, session)) {
      return Boolean.FALSE;
    }

    if (!hasSig) {
      Buffer buf = session.createBuffer(SshConstants.SSH_MSG_USERAUTH_PK_OK);
      buf.putString(alg);
      buf.putRawBytes(buffer.array(), oldPos, 4 + len);
      session.writePacket(buf);
      return null;
    } else {
      Buffer buf = new ByteArrayBuffer();
      buf.putBytes(session.getKex().getH());
      buf.putByte(SshConstants.SSH_MSG_USERAUTH_REQUEST);
      buf.putString(username);
      buf.putString(service);
      buf.putString(UserAuthPublicKeyFactory.NAME);
      buf.putBoolean(true);
      buf.putString(alg);
      buffer.rpos(oldPos);
      buffer.wpos(oldPos + 4 + len);
      buf.putBuffer(buffer);
      verif.update(buf.array(), buf.rpos(), buf.available());
      if (!verif.verify(sig)) {
        throw new Exception("Key verification failed");
      }
      return Boolean.TRUE;
    }
  }