To improve security and simplify financial transactions in electronic communications environments, a cryptographic Private Key is securely stored in a storage device of a user. A Public Key Certificate corresponding to the Private Key is also created and can be stored in an online repository for merchant access. The Public Key Certificate identifies a payment card of the user, and is signed by or on behalf of a financial institution issuing the payment card. When initiating a payment card transaction with a merchant, a data item is signed using the Private Key. The signed data item and the Public Key Certificate are conveyed to the merchant, which enables the merchant to authenticate the transaction without needing to communicate with the user's financial institution, and while avoiding the inconvenience and privacy issues associated with obtaining other card details and user details.