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 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.