There are some important "numbers" printed on the card, and its importance can be said to be as important as any card swiping technique. Before becoming a "card god", we must not only "know" our own credit cards "well", but also be able to identify the key information in the credit cards and "keep it secret" from others.

Recently, Mr. Lin encountered a special credit card. After paying for a large-limit credit card, the card application sent him a "fake" credit card. Not only did the card look the same as an ordinary credit card, but the balance could even be checked at the bank's ATM machine. However, for bank staff, it is easy to identify the authenticity of a card at a glance. How did they do it?

The answer is to look at the credit card number. Although we often need to enter a 16-digit card number when swiping a card online, most people will not delve into the meaning behind these numbers to understand the "mystery". In fact, we don’t have to remember it 100%, but we must be aware of it.

In the 16-digit card number (up to 19 digits), although four numbers are a group, in fact, we can divide it into three parts. The first part is 1 to 6 digits, which is the card-issuing bank identification code, that is, the BIN (BankIdentificationNumber) code. The second part is a 7 to 15-digit number, which represents the bank account. Its meaning is customized by the card issuing bank, and each bank has different definition standards. The third part is only the last digit of the card number, the 16th digit, which is the verification code of the credit card number. This number can be used to verify the validity of the card number.

Among them, by querying the BIN code, we can know the issuing and bank of our card, as well as the type of card. Among them, the BIN number starting with "4" is Visa card; the BIN number starting with "5" is MasterCard; the BIN number starting with "6" is China UnionPay card; the one starting with "35" is JCB card; the one starting with "37" is American Express. In Mr. Lin's case, his card starts with the character "6" and there is a VISA logo on the bank card. However, the first digit of the VISA card is "4" and the bank card starting with "6" is a UnionPay card, so it should only have the UnionPay logo.

In addition to the above simple methods to identify the authenticity of credit cards, there is also a "high IQ" method. Many people don’t know that the last digit on a credit card is not random, but can be determined through an algorithm. The most commonly used algorithm was invented by IBM engineer Luhn in 1954 and has now become an international standard for credit cards. It is called the Luhn algorithm, or the modulo 10 algorithm. In other words, if the last digit of the credit card's verification code is inconsistent with the result obtained by the algorithm, the card can be determined to be fake.

The first step is to sort the 16-digit card number from left to right, select the odd digits and multiply them by 2, and then add the ones and tens digits of the two-digit number. For example, if the third digit of a credit card is 6, multiply it by 2 to get 12, and add the ones and tens digits to get 3.

In the second step, add the number obtained above to the even digits in the card number to get a total, and take the ones digit. If the sum is 83, only take the units digit of 3.

The third step is to subtract the single digit obtained above from the number 10 (3 in the example). The resulting number (7) is the last check code in the card number.

Take card number 7 as an example, pick out the odd digits in the first 15 digits, and follow the first step to get a new sequence of numbers (the even digits remain unchanged), and then add the sequence The sum of all the numbers in is 83, only the single digit 3 is taken. Finally, subtract 3 from 10 to get the last digit of the credit card, 7. The conclusion is: the card number passed the test.

Every credit card is indispensable with these three sets of important numbers: card number, expiration date, and security code. However, it would be a mistake to assume that just because these numbers are printed "statefully" on the card, this is just routine information. In fact, these three sets of numbers can be said to be the "open secrets" of the credit card. If others know it, it is equivalent to someone else holding the credit card.

Perhaps you have seen that some cautious cardholders will cut a small piece of tape and stick it on the last three digits of the signature on the back of the credit card to prevent leakage. What they stick on is the credit card security code, which is usually the three digits after the last four digits of the card number in italics. The main function of the credit card security code is to serve as a security code for credit cards when conducting online or telephone transactions, to confirm that the payer actually holds the credit card during the transaction.

Since some websites, especially overseas websites, do not require a password when paying on a credit card network, and transactions can be completed using only the card number, expiration date and credit card security code, so the importance of the credit card security code is almost the same as that of a credit card. password.

Therefore, cardholders should be more careful and vigilant when presenting or swiping their cards to avoid being seen or photographed by others. After each purchase, the cardholder must also keep the credit card receipt. If these transaction receipts are picked up by criminals, the credit card will be easily cloned and stolen. In addition, cardholders should also fully protect their credit cards and ensure that the cards never leave their bodies. They should not let the cards leave their sight when making purchases, and they should not put their credit cards in photos posted on their WeChat Moments.

The validity period is usually expressed on the credit card surface in the format of ValidFrom (MM/YY); ValidThru (MM/YY). The significance of the validity period actually lies in the bank's risk control, which can reduce risks such as cardholders failing to report the loss after losing the card, long-term malicious overdrafts, and other people using the credit card fraudulently after the cardholder's death.

The validity period of a credit card is generally three years, and for some banks it is five years. Therefore, many cardholders born in the 1990s may have never encountered the expiration of their credit cards. Although before the end of the validity period, banks usually remind users by email, text message, letter, etc. However, this does not mean that we can "ignore" the existence of this number on the credit card.

First, changes in the recipient address, contact information and other information must be notified to the bank in a timely manner. After the expiration date, most banks will mail the new card to the residential or work address that the user filled in when they originally applied for the card. Especially if there is a job change, you should contact the bank to change the address so that you can receive the new card normally.

Second, if you do not want to continue using your card after the expiration date, you should contact the credit card service center in time. If you think the credit card has expired and ignore it, the bank will still mail out a new card and start calculating the annual card fee for the new year.