code: public PrivateKey unwrapPrivateKeyByKey(byte[] key,Key unwrapKey)
  	{
  		try {
      		if(key==null || key.length<=0 || unwrapKey==null)
      		{
      			return null;
      		}
  			Cipher cipher=Cipher.getInstance(algorithm);
  			//使用私钥包裹模式
  			cipher.init(Cipher.UNWRAP_MODE,unwrapKey);
  			return (PrivateKey) cipher.unwrap(key, algorithm,Cipher.PRIVATE_KEY);
  		} catch (Exception e) {
  			log.error(e.getMessage(),e);
  		}
      	return null;
  	}
docs: 使用密钥解包密钥
  @param key
  @param unwrapKey
  @return