EMV Offline Approval/Decline

Question

I'm developing an interface to a VeriFone VX terminal. Although, this is really a general EMV question. Our processor has a zero floor limit, so it will always be sent online. However, in case it ever changes, how do you know (what tags) if the transaction was approved or declined offline? Or, in other words, how do you know to go online or not?

Answer 1

how do you know (what tags) if the transaction was approved or declined offline? Or, in other words, how do you know to go online or not?

The terminal has to decides either to proceed the transaction offline, to go online or to reject the transaction. Here terminal send a command (AC) to the card and response of this command helps terminal to decide the action next followed.

Decision making is depend on three fields -
1) - Issuer Action Code
2) - Terminal Action Code
3) - TVR

IAC, TAC and TVR have the same structure. For more to know this data you can see EMV BOOK 3

IAC Usage Example-

suppose IAC-ONLINE (TAG - 9F0F) = 08 00 00 00 00 , 
here byte 1 bit 4 is on i.e. offline DDA Failed , 
Here Issuer want to go online if offline DDA Failed.

when terminal perform DDA and it fails, it set corresponding bit in TVR that means TVR says- offline DDA is failed for this card. now terminal check IAC online and found DDA_Failed bit is on and same on in TVR, here terminal decision would be to go online and then it send a Gen AC command to card with p1 = 80 ( ARQC - Online authorisation requested).

Coding of P1 as below

Ex- Gen AC command

C: 80 AE 80 00 other data
R: SW1/SW2=9000 (Normal processing: No error) Lr=32
77 1E 9F 27 01 80 9F 36 02 02 13 9F 26 08 2D F3
83 3C 61 85 5B EA 9F 10 07 06 84 23 00 31 02 08

. Now decision is made by card, Terminal get card decision in the response of Gen AC command. Card return tag 9F27 - Cryptogram Information Data. here card return 80 i.e. cards wants transaction to go Online.

Really your question is important and you need to read more spec for clarity on this topic. Please checks EMV BOOKs, for more in this topic. also can read - Terminal action analysis or Card Action analysis