If it is a China Merchants Bank credit card, the credit card security code is a set of 3 or 4 digits on the credit card. Its generation method is that the bank extracts the account number, validity period and service code of the card, arranges them and then calculates them through a series of complicated algorithms. After this set of numbers is generated, only the issuing bank and the holder of the bank card know what this number is. Credit card security code is the security code of credit card for online or telephone transactions. It is usually used to prove that the payer has a credit card at the time of transaction, thus preventing credit card fraud.

The security code of 1.VISA card is called CVV2(CardVerificationValue2), which has 3 digits and is printed on the last 4 digits of the signature column on the back of the credit card.

2.MarsterCard's security code is called CVC2(CardValidationCode2), which has 3 digits and is printed on the last 4 digits of the signature column on the back of the credit card.

3. The security code of 3.DiscoverCard is called CardmemberID ID, which has 3 digits and is printed on the signature column on the back of the credit card.

4. The security code of 4.AmericanExpress is called CID (CID(cardentificationnumber), which has 4 digits and is printed on the front of the credit card.

5. The security code of China UnionPay is called CVN2(CardValidationNumber2), with 3 digits and 4 digits printed on the back of the credit card.

6. The security code of 6.JCB card (JapanCreditBureau) is called CAV2(CardAuthenticationValue2), which has 3 digits and is printed on the last 4 digits of the signature column on the back of the credit card.

What do the seven digits on the back of the credit card mean?

1, credit card basics

Credit consists of a series of 16 digits. The card starting with 4 is VISA, the card starting with 5 is MasterCard, JCB card and American Express card usually start with 3, and the most common card of China UnionPay starts with 62.

2, the meaning of credit card number arrangement

Taking the Great Wall Global Connect VISA chip credit card of China Bank as an example, we dissect the digital meaning of the credit card, which consists of *** 16 digits, a group of four digits and a group of * * *. So what does this arrangement mean? Let's look at the table below:

In this table, we can clearly see that the 1-6 bit in the bright yellow field is the identification code of the issuing bank, which is the familiar BIN code; Huang Tu domain 7- 15 is a bank account (except American Express, the same below), and its meaning is defined by the issuing bank. The definition standards of each bank are different, so I won't elaborate on them one by one. The 16 bit of the grass green field is the check code, which is called checkdigit in English. It is used to verify the validity. I'll talk about how to calculate this number later.

3. Issuer identification code (BIN code)

Let's first understand what is the issuer identification code (BIN code). Many card friends know that this is the 6-digit number assigned to the bank by the card organization, but how it came from may not be clear to many people.

The first six digits are called BIN, which is the abbreviation of English BankIdentificationNumber; This set of numbers, also known as IIN, is the abbreviation of the English IssueIdentificationNumber (IssueIdentificationNumber), which is formulated according to the ISO/IEC78 12 document. These numbers can help cardholders and merchants identify the issuer of bank cards. Banks that meet the ISO/IEC78 12 standard usually have 16 digits, which can reach 19 digits at the longest. The standard structure is shown in table 1.

According to ISO/IEC78 12, the first place is strictly MII? -MajorIndustryIdentifier, which is the main industry identifier, can easily help us identify the industry to which the card belongs. For example, numbers starting with 3 are allocated to tourism, entertainment and banking/finance, numbers starting with 4 and 5 are fully allocated to banking/finance, and numbers starting with 6 are allocated to business and banking/finance. The 2-6 digits of are called IIN, which is the identification number of the issuer. Of course, we are talking about bank cards here, so we don't need to be so detailed. Interested friends can go online to find information themselves. For simplicity, we still use BIN code to address the first 6 digits of the bank card.

IIN database and its members are currently managed by American National Standards Institute (ANSI) and updated once a month. The American National Standards Institute is responsible for assigning IIN ranges to distribution networks. UnionPay will apply to the organization for an international standard card number starting with 62. There are many websites that provide BIN code queries. As long as we enter the first 6 digits of the card, we can know our issuing country and bank and the card type. Here I recommend a BIN code query website for everyone. Interested friends may wish to check their card types. Of course, the results are for reference only.

4.No. 7- 15.

The 7th-15th position of a credit card, that is, the bank account, is defined by the bank itself, and the rules of each bank are different. You just need to understand that this is your own bank account. Here, I want to say a little more about the Great Wall Global Pass Card of China Bank. This set of accounts of Great Wall Card is very interesting. He defined 7-8 digits as the identification number of provincial card issuing banks, such as 3 1 in Shanghai, 32 in Jiangsu and so on. The remaining 9- 15 digits are your account number, and the last digit is the check code. Let's take a look at Table 2 below to understand the structure and characteristics of the Great Wall Card of China Bank:

By the way, I will provide you with the identification number of the provincial card issuer of Great Wall Global Card:

Beijing 1 1, Tianjin 12, Hebei 13, Shanxi 14, Inner Mongolia Autonomous Region 15, Liaoning 2 1, Jilin 22, Heilongjiang 23 and Shanghai 3/. Guangdong 44, Shenzhen 48, Guangxi 45, Hainan 46, Chongqing 50, Sichuan 5 1, Guizhou 52, Yunnan 53, 54, Shaanxi 6 1, Gansu 52, Qinghai 53, Ningxia 64 and Xinjiang 65.

Interested friends may wish to compare the Great Wall card in their hands.

5, the last check code

Now there is only the last check code of the card, but before introducing the sixteenth check code, let's learn a proper term-Luhn algorithm.

Luhnalgorithm, also known as "modulus 10 algorithm" (MODU 10 or Mod 10), is a simple checksum algorithm, which is generally used to verify identity codes, such as the issuer's identity code, the international mobile equipment identification number (IMEI), the national provider identification number of the United States or the social security number of Canada. Invented by IBM scientist HansPeterLuhn,/kloc-0 applied for a patent on June 6, 954, and granted on August 23, 960, with the U.S. patent number of 2,950,048.

This algorithm has been widely used, such as ISO/IEC78 12- 1 standard related to our credit card. It is designed to prevent accidental mistakes, not malicious attacks. Many credit cards and many government identification numbers use this algorithm to extract valid numbers from a series of random numbers, but China UnionPay does not use this algorithm, and it is still unknown what algorithm to use.

Let's use the truth in this paper to understand the characteristics of this algorithm and see how the last check code, that is, check code 9, is calculated.

Calculation steps:

1. The third column, starting from the parity bit, from right to left, multiplies the even number by 2, and then adds the single digits of the two digits to the ten digits;

2. In the fourth column, the odd digits of the obtained number and the original number string are added to obtain 71;

3. The unit number of the result is 1.

4. Subtract 1 0 from1to get 9, which is the last check code in the real card.

Another algorithm is to calculate the sum of 7 1 according to the above step 1-2, and then:

1. Result 7 1 times 9 to get 639.

2. The single digit of the result is 9, which is the check code.

Now we know that the last check code of the credit card is calculated by Luhn algorithm, and its function is to verify the validity of the card, instead of randomly generating a number in the bank computer and printing it out. Some popular online credit code generators also use this algorithm to generate credit codes. Although this algorithm is effective, it is still a fake card and cannot be used for real online transactions.

Is there 7 digits behind China Merchants Bank's credit card? Where can I see it?

If it is a credit card of China Merchants Bank, the number on the back of the card is related to the security of the account. There is no other way to find these numbers unless you report the loss of your card or find the original card.

What are the seven numbers on the back of my China Bank credit card for?

The first four digits of the seven digits on the back of the card are the mantissa of your credit card, and the last three digits are mainly used for telephone transactions. You can provide information such as expiration date and password on the back of the card to complete the payment.

The above contents are for your reference. Please refer to the actual business regulations.

If you have any questions, please contact online customer service of Bank of China.

You are cordially invited to download and use China Bank Mobile Banking APP or China Bank Cross-border GOAPP to handle related business.

So much for the introduction of seven-digit credit cards.