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ISO 8583
We covered the ISO 8583 basics in an earlier article. This post explains the ISO 8583 message structure in detail: every ISO 8583 message consists of three main parts - the MTI (Message Type Indicator), the Bitmap, and the Data Elements.
ISO 8583
F64 — Message Authentication Code (MAC): verifies the origin and text of the message between the sender and the receiver.
Merchant & POS
Introduction: When a card (credit card/debit card/prepaid card) is used at an ATM or POS, data must be carried securely between systems. For example, in a store sale, the POS initiates the transaction, which must reach the cardholder's bank intact.
Payment Systems
TCR stands for Transaction Record Component, the packets that carry transaction information in a clearing system. Transaction types in a clearing file are distinguished by transaction code and usage code values, and this data is sent inside TCR packets.
Merchant & POS
In payment systems, every exchange between POS devices and bank or payment institution systems runs on a specific messaging standard, generally based on ISO 8583. However, each country, bank, or switch network defines its own version of this standard.
ISO 8583
F47-ADDITIONAL DATA (NATIONAL) is the field reserved for domestic additional information. In Turkey, it carries the BKM Unique ID in authorization transactions and data specific to KKPT (card-to-card transfer) transactions.
Payment Systems
One of the most notable recent developments in card payments is that contactless limits are no longer fixed and can be managed dynamically per customer. Mastercard and Visa are taking different but complementary approaches, and ISO 8583 may need to evolve with them.
Merchant & POS
In EMV-based debit card transactions, PIN verification is decisive for both security and liability. What happens when a card that only supports online PIN is sent to the issuer without a PIN, and the issuer approves it? Who owns the risk?
Merchant & POS
BKM has changed the domestic transaction flows for contactless transactions above and below the CVM limit. For above-limit transactions, the issuer can now ask the cardholder to re-enter the PIN instead of terminating the transaction after an incorrect PIN (DE39 = 55).
Merchant & POS
The System Trace Audit Number (STAN) is a number assigned by the third-party system (ATM or POS) to help uniquely identify a transaction. It is generated in the range 000001 to 999999. Each new authorization message needs a new STAN; retries reuse the original STAN.
Payment Systems
The domestic authorization flow for below-CVM-limit online contactless transactions has changed. Issuers can now ask the cardholder for a PIN or request card insertion instead of simply approving or declining. This post explains the CVM list and the new DE48 PDS22 and DE39 = 65 message flows.
ISO 8583
F34 — Primary Account Number, Extended: this field is filled when the card number cannot be placed in F2 because it is longer than 19 digits or contains special characters.