120 to the merchant's computer 104, in a first step. The merchant's computer 104 forwards the consumer's payment request over internet path 122 during a second step to an acquirer gateway 106 operating on behalf of the acquirer bank 108. The acquirer gateway 106 passes the consumer's payment request to the acquirer bank 108 over a private network path 122′. The acquirer bank 108 sends the consumer's payment request to the card issuing bank 112 over the private network path 124 to check whether the consumer's credit or debit card account is active and sufficient for the proposed transaction with the merchant. The issuing bank 112, as the card issuer, authorizes the transaction in a message sent over private path 126 to the acquiring bank 108. The acquiringbank 108 sends the transaction authorization over private path 128′ to the acquirer gateway 106, signing the message with the acquiring bank's digital signature. The acquirer gateway 106 forwards it over the internet path 128 to the merchant, authorizing the merchant to proceed with the transaction. Once the merchant has received the transaction authorization from the acquirer gateway 106, the merchant completes the sales transaction with the consumer. Then later, the merchant sends a message over internet path 142 to the acquirer gateway 106 to capture the transaction and get paid. The acquirer gateway then sends a payment message over path 144 to the merchant. The acquiring bank 108 may participate in some or all of the payment steps over private network paths 142′ and 144′. Then, at