Security for contactless transactions
A method of performing a contactless transaction between a payment device and a terminal is described. The method comprises establishing a data connection between the payment device and the terminal and then establishing if the payment device and the terminal both support an enhanced security architecture. If they do not, they will then perform the contactless transaction according to a basic transaction flow using a first cryptographic system. If they do, they will perform the contactless transaction according to an enhanced transaction flow using a second cryptographic system. The first cryptographic system and the second cryptographic system comprise different asymmetric cryptographic systems. Suitable payment devices and terminals, and methods at the payment devices and terminals, are described.
1. A method at a payment device of performing a contactless transaction with a terminal, the method comprising:
establishing a data connection with the terminal;
establishing if the payment device and the terminal both support an enhanced security architecture; and
if not, performing the contactless transaction according to a basic transaction flow using a first cryptographic system; but
if so, performing the contactless transaction according to an enhanced transaction flow using a second cryptographic system;
wherein the first cryptographic system and the second cryptographic system comprise different asymmetric cryptographic systems.
2. The method of claim 1 , wherein the first cryptographic system comprises RSA cryptography whereas the second cryptographic system comprises ECC cryptography.
3. The method of claim 1 , wherein the payment device provides the terminal with a certificate for both public keys of both the first cryptographic system and the second cryptographic system asymmetric cryptographic systems.
4. The method of claim 1 , wherein the second cryptographic system additionally uses AES.
5. The method of claim 4 , wherein the enhanced transaction flow uses AES session keys.
6. The method of claim 5 , wherein the enhanced transaction flow uses a first AES confidentiality session key for establishing a confidential channel between the payment device and the terminal and an AES integrity session key for establishing data integrity.
7. The method of claim 1 , wherein in the enhanced transaction flow the payment device receives a terminal public key from the terminal, and provides a payment device public key with an encrypted blinding factor to the terminal to establish a shared secret using a blinded Diffie-Hellman key exchange.
8. The method of claim 1 , wherein in the enhanced transaction flow the payment device receives a command to generate an application cryptogram for the transaction.
9. The method of claim 8 , wherein the payment device provides the application cryptogram and additional transaction related data in a data envelope protected by a Message Authentication Code using an AES integrity session key.
10. The method of claim 8 , wherein cardholder verification choices are received from the terminal with the command to generate the application cryptogram, and wherein the payment device provides a selected cardholder verification choice with the application cryptogram.
11. A method at a terminal of performing a contactless transaction with a payment device, the method comprising:
establishing a data connection with the payment device;
establishing if the payment device and the terminal both support an enhanced security architecture; and
if not, performing the contactless transaction according to a basic transaction flow using a first cryptographic system; but
if so, performing the contactless transaction according to an enhanced transaction flow using a second cryptographic system;
wherein the first cryptographic system and the second cryptographic system comprise different asymmetric cryptographic systems.
12. The method of claim 11 , wherein the first cryptographic system comprises RSA cryptography whereas the second cryptographic system comprises ECC cryptography.
13. The method of claim 11 , wherein the second cryptographic system additionally uses AES.
14. The method of claim 13 , wherein the enhanced transaction flow uses AES session keys.
15. The method of claim 14 , wherein the enhanced transaction flow uses a first AES session key for establishing a confidential channel between the payment device and the terminal and a second AES session key for establishing data integrity.
16. The method of claim 11 , wherein in the enhanced transaction flow the terminal provides a terminal public key to the payment device, and then receives from the payment device a payment device public key with an encrypted blinding factor to establish a shared secret using a blinded Diffie-Hellman key exchange.
17. The method of claim 11 , wherein in the enhanced transaction flow the terminal commands the payment device to generate an application cryptogram for the transaction, wherein the terminal provides cardholder verification choices with the command to provide the application cryptogram, and receives from the payment device a selected cardholder verification choice with the application cryptogram.
18. A payment device adapted to perform a contactless transaction with a terminal, wherein the payment device is adapted to:
establish a data connection with the terminal;
establish if the payment device and the terminal both support an enhanced security architecture; and
if not, to perform the contactless transaction according to a basic transaction flow using a first cryptographic system; but
if so, to perform the contactless transaction according to an enhanced transaction flow using a second cryptographic system;
wherein the first cryptographic system and the second cryptographic system comprise different asymmetric cryptographic systems.
19. The payment device of claim 18 , wherein the payment device is a passive device.
20. The payment device of claim 19 , wherein the payment device is a payment card.