A user has two asymmetric crypto-keys, the first having a first private key and the second having a second private key, both of which are split into a first private key portion corresponding to a password of the user and to a computation. However, the computation of the first private key portion of the first and the second private keys have different levels of complexity. First and second messages from the user encrypted with the first private key portion of, respectively, the first private key and the second private key, are received centrally. A second private key portion of, respectively, the first private key and the second private key is applied to the received first and the received second messages, as applicable, to authenticate the user at, respectively, a first level of authentication security and a second level of authentication security which is greater than the first level.