Difference between 9f5d and 9f79 of EMV/PBOC

Reprinted please indicate the source

Author: Pony

Strictly speaking, the 9f5d concept is qpboc, And the offline balance is available. 9f79 is called an electronic cash balance. since qpboc and e-cash are not completely independent concepts, and the two tags both represent balances, these two concepts are often difficult to distinguish.

 

That's right. It's hard for me to tell the difference. I am not very clear about the differences between the two tags. I just want to explain their respective purposes and application scenarios based on my own understanding.

 

First, 9f5d and 9f79 should usually be equal. Why is it generally because 9f5d is not 9f79 when ctta (total offline transaction amount) is required. when it comes to ctta, we need to talk about cttaul (the total amount of accumulated offline transactions is limited ). to put it simply, when qpboc is offline, there are rules for the card to check whether it is "legal". These rules are divided into three categories: small, small, or ctta, and small and ctta. the three specific descriptions can be de-translated into different categories. The 9f5d card calculation method is different, as shown below:

Small, 9f5d = 9f79

Small or ctta, 9f5d = 9f79 + CTTAUL-CTTA

Small & ctta, 9f5d = CTTAUL-CTTA

 

Taking small or ctta as an example, this method is actually the most loose in the three methods, which means to first check whether your money in e-cash is sufficient. If it is enough, use this. if the electronic cash condition is not met, check whether the money in ctta meets the condition. If yes, you can also use it. this is also the basis for the above formula. in this case, the ctta is equivalent to virtualizing another "balance" on the card. I am not doing the card, and this part is not particularly understood. Is it used for overdraft?

 

In addition, according to the PBOC 14 specification, 9f5d only appears in the <Non-Contact IC Card Payment Specification>, so we can say at least, 9f5d only appears in the non-connected transaction interface, which is also consistent with the so-called flash payment or fast transaction, because after the transaction shows the balance, if 9f79 is used, the get Data command is also sent, and 9f5d is missing. It is returned to the terminal at GPO.

 

Where can 9f79 be used? It is usually used to intuitively display the balance. For example, if a function is provided on the terminal, it is called an electronic cash balance query, the offline balance is usually the value of 9f79 retrieved through get data. in fact, I also have some questions. As mentioned above, the available offline consumption amount 9f5d on the card is sometimes different from 9f79. Will the balance shown here mislead people? For example, I found that the balance on the card is 100, but it may not be possible to successfully make an offline payment of 100.