code: public byte[] sign(byte[] data) {
  		lock.lock();
  		try {
  			signature.initSign(this.privateKey);
  			signature.update(data);
  			return signature.sign();
  		} catch (Exception e) {
  			throw new CryptoException(e);
  		} finally {
  			lock.unlock();
  		}
  	}
docs: 用私钥对信息生成数字签名
  
  @param data 加密数据
  @return 签名