The invention provides a method, apparatus, computer readable medium and signal which allows the usage of devices containing PKI private keys such as PKI-enabled smart cards or USB sticks to authenticate users and to sign transactions. The authenticity of the user and/or the message is verified. Furthermore the operation (authentication and/or signing) occurs without the need for an application to have some kind of a direct or indirect digital connection with the device containing the private key. In other words a digital connection that would allow an application to submit data to the card for signing by the card's private key and that would allow retrieving the entire resulting signature from the card is not required. In addition the operation occurs without the need for the PKI-enabled device containing the private key (e.g. a PKI smart card or USB stick) to either support symmetric cryptographic operations or to have been personalized with some secret or confidential data element that can be read by a suitable reader.