Abstract: A secure method of conducting an electronic transaction over a public communications network is provided which utilizes a pseudo-expiration date in the expiration date field of an authorization request. One of the preferred methods comprises: generating a per-card key associated with an account number; generating a message authentication code using the per-card key; converting the message authentication code into a pseudo expiration date; generating an authorization request for the transaction, the request having an expiration date field containing the pseudo expiration date; and verifying the message authentication code based on the pseudo expiration date.