ISO8583 Foundations Quiz

1. You receive a message starting with `0420`. Without looking at anything else, what do you know about this message?

It's a 1987-spec reversal request from an issuer It's a 1987-spec reversal advice from an acquirer It's a 2003-spec authorization response It's a network management message

2. What is the purpose of the bitmap in an ISO8583 message?

To encrypt the message payload To indicate which data elements are present in the message To specify the message routing information To validate the message integrity (checksum)

3. A terminal sends an authorization request (0100) but doesn't receive a response within 30 seconds. What should happen next?

Send another 0100 with the same STAN Send a 0400 reversal to cancel the potentially-processed transaction Wait indefinitely for the response Send a 0800 network management message

4. You see an MTI of `0101`. How does this differ from `0100`?

0101 is a response, 0100 is a request 0101 is from the issuer, 0100 is from the acquirer 0101 is a repeat transmission (retry), 0100 is the first attempt 0101 uses 2003 spec, 0100 uses 1987 spec

5. In an ISO8583 message, how do you know if a secondary bitmap (fields 65-128) is present?

The MTI version digit is set to 2 Bit 1 of the primary bitmap is set to 1 The message length exceeds a certain threshold Field 64 contains a special marker

6. Which fields are typically used to match an authorization response (0110) back to its original request (0100)?

Only the card number (DE2) STAN (DE11), date/time (DE12/13), and Acquirer ID (DE32) Only the response code (DE39) The bitmap pattern

7. You're parsing a message and the primary bitmap is `F2 34 00 01 08 E1 80 00`. Which of these fields is definitely NOT present?

Field 2 (PAN) Field 3 (Processing Code) Field 5 Field 65 (Secondary bitmap field)

8. What response code (DE39) indicates the transaction was approved?

01 00 05 51

9. Why is ISO8583 still used instead of modern formats like JSON or Protocol Buffers?

It's more secure than modern formats Compact encoding, low latency, and massive backward compatibility across global infrastructure It supports more data types than JSON It was mandated by government regulations

10. What does an MTI of `0800` typically represent?

Authorization request Reversal request Network management request (sign-on, echo test, or key exchange) Financial advice

11. You see the hex bytes `30 31 30 30` at the start of a message. What MTI is this?

3010 (financial request) 0100 (authorization request) - ASCII encoded 0100 (authorization request) - BCD encoded Invalid MTI

12. Your parser reads the first bytes of a TCP stream as: `00 C8 30 31 30 30 72...`. What's likely happening?

The message is corrupted There's a 2-byte length header (200 bytes) before the ASCII MTI This is a BCD-encoded MTI The bitmap is malformed

13. What is Field 1 (DE1) in an ISO8583 message?

The primary bitmap The secondary bitmap (when present) The message type indicator Reserved for future use

14. A processing code (DE3) of `011020` means what?

Purchase transaction from default account Cash withdrawal from savings to checking Refund to credit card Balance inquiry

15. An amount field (DE4) contains `000000010000` and the currency code (DE49) is `392` (JPY). What's the actual amount?

100.00 JPY 10000 JPY 1000.00 JPY 10.000 JPY