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.
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 the extended data credit card is equivalent to the ID card of the credit card, and we can use this code for consumer transactions. You don't need a password to shop on overseas websites. As long as the buyer provides the account number and security code, the transaction can be completed. In China, there are also merchants signing contracts with banks, but you don't need a credit card password, you only need a security code to complete the telephone transfer.
Because the encryption algorithms of different banks are different, some fake cards illegally made by using the obtained bank card information can be identified and cannot be used when the issuing bank decrypts them.
Baidu encyclopedia-credit card security code