EMV chip AQRC generate

[anhlong]

The principle of operation of the DDA is as follows
(simplified and omitting many details):
1) the terminal sends a unpredictable number to the card, along with some other data for signing
2) the card signs the data transmitted to it from the terminal and transfers the signature of this data in response to the terminal
3) the terminal decrypts the encrypted data received from the card
4) the terminal verifies the data transmitted in advance of the card with the data obtained from the signed and decrypted data
5) if the unpredictable number transmitted by the terminal to the card differs from the unpredictable number in the decrypted data received from the card, the transaction is canceled
a) each terinil generates its own unique unpredictable number.
b) a unpredictable number is a number that generates terminal
c) the card signs unpredictable number and transfers the signature to the terminal for verification.
d) new operation = new unpredictable number
e) new terminal = new unpredictable number
f) a new transaction initialization involves generating a new unpredictable number.
g) the unpredictable number generated by the terminal has value in the very transaction for which it is generated
due to the fact that DDA uses the private key of the card:
the bank issuer (simplified and omitting many details) creates 2 pairs of keys:
1) public key card + private card key
2) bank's public key + bank's private key
public key of the card and public key of the bank
become known to the terminal during the execution of the transaction.
bank's private key and private card key never become known to the terminal
3) the payment system (visa, mastercard ...) has its own, public key + private key
a) - the public key of the system (visa, mastercard ...) is entered into the terminal by the bank acquirer
b) - before issuing its cards, the issuer bank - sends its public bank key to the payment system
b1) the payment system signs with the private key the public key of the issuing bank and sends the received certificate back to it
с) the bank issuer signs by his with the private key the public key of the card and receives the certificate of the public key of the card
the bank’s public key certificate and the card’s public key certificate are recorded on the card upon personalization
through a mathematical connection between private keys and public keys, as well as through a mathematical connection between certificates - the authenticity of the card are verified, when used, in the terminal
terminal receives signed data and can check :
card issued by a bank that is certified by the payment system
having established that the public key of the card can be trusted
the terminal uses this public key to decrypt the encrypted data and compare the unpredictable number from this data with the unpredictable number that the terminal transmitted to the card half a second ago back