Abstract: A system for making a purchase by a customer from a merchant, wherein an electronic message represents an instruction for payment from an account with a financial institution, includes a method of: associating a public key with identity information regarding the account; receiving by the merchant both encoding information for the electronic message and the identity information; forwarding by the merchant the electronic message, encoding information, and identity information; upon receipt of the electronic message, the encoding information, and identity information, retrieving the public key associated with the identity information; and determining a validation result as a function of the electronic message, the encoding information, and the retrieved public key. Upon successful validation, an account authorization is performed or payment from the account is made.