Efficient methods for protecting identity in authenticated transmissions

1. An access device comprising:

a processor; and

a non-transitory computer-readable storage medium comprising code executable by the processor for implementing a method comprising:

receiving a message including a blinded user device public key and encrypted user device data from a user device, wherein the blinded user device public key is generated by the user device obfuscating a user device public key using a cryptographic nonce, the cryptographic nonce being a randomly generated value or a pseudo-randomly generated value, and wherein user device data is encrypted by the user device using a shared secret to obtain the encrypted user device data, the shared secret being different from the cryptographic nonce;

generating the shared secret using an access device private key and the blinded user device public key, the access device private key associated with an access device public key; and

decrypting the encrypted user device data using the shared secret.

2. The access device of claim 1 , wherein the method further comprises:

sending a request message including the access device public key to the user device, wherein the user device is configured to generate the shared secret using the access device public key without using any other keys from the access device, and wherein the generating of the shared secret by the access device is not based on any other keys from the user device besides the blinded user device public key.

3. The access device of claim 1 , wherein the access device public key and the access device private key form an ephemeral key pair, and wherein the method further comprises deleting the ephemeral key pair after the generating of the shared secret.

4. The access device of claim 1 , wherein the method further comprises generating a session key using the shared secret, and wherein the decrypting of the encrypted user device data uses the session key.

5. The access device of claim 1 , wherein the user device data comprises a user device certificate comprising a user device public key and the cryptographic nonce used to generate the blinded user device public key, and wherein the method further comprises:

validating the user device certificate;

generating a second blinded user device public key using the user device public key and the cryptographic nonce; and

comparing the second blinded user device public key with the blinded user device public key, wherein the user device is authenticated if the second blinded user device public key matches the blinded user device public key.

6. The access device of claim 1 , wherein the shared secret is a first shared secret, and wherein the method further comprises:

generating a second shared secret using the first shared secret; and

associating the second shared secret with the user device, wherein the second shared secret is used to decrypt subsequent user device data received from the user device.

7. The access device of claim 1 , wherein the method further comprises conducting a transaction using the user device data.

8. The access device of claim 1 , wherein the access device is in a system, the system further comprising:

the user device, wherein the user device is configured to:

receive the access device public key;

generate the shared secret using the access device public key, a user device private key associated with the user device public key, and the cryptographic nonce;

generate the blinded user device public key by obfuscating the user device public key using the cryptographic nonce;

encrypt the user device data using the shared secret; and

send the message including the encrypted user device data and the blinded user device public key to the access device.

9. The access device of claim 1 , wherein the method further comprises:

sending a request message including the access device public key to the user device; and

determining that the user device has entered a contactless field of the access device, wherein the sending of the request message occurs in response to the determining that the user device has entered the contactless field of the access device, and wherein the request message is sent via the contactless field.

10. A computer-implemented method comprising:

receiving, by an access device, a message including a blinded user device public key and encrypted user device data from a user device, wherein the blinded user device public key is generated by the user device obfuscating a user device public key using a cryptographic nonce, the cryptographic nonce being a randomly generated value or a pseudo-randomly generated value, and wherein user device data is encrypted by the user device using a shared secret to obtain the encrypted user device data, the shared secret being different from the cryptographic nonce;

generating, by the access device, the shared secret using an access device private key and the blinded user device public key, the access device private key associated with an access device public key; and

decrypting, by the access device, the encrypted user device data using the shared secret.

11. The computer-implemented method of claim 10 , further comprising:

sending, by the access device, a request message including the access device public key to a user device, wherein the user device generates the shared secret using the access device public key, wherein the generation of the shared secret by the user device is not based on any other keys from the access device besides those included in the request message, and wherein the generating of the shared secret by the access device is not based on any other keys from the user device besides those included in the message.

12. The computer-implemented method of claim 10 , wherein the access device public key and the access device private key form an ephemeral key pair, the method further comprising deleting the ephemeral key pair after the shared secret is generated.

13. The computer-implemented method of claim 10 , further comprising generating, by the access device, a session key using the shared secret, wherein the decrypting of the encrypted user device data uses the session key.

14. The computer-implemented method of claim 10 , wherein the user device data comprises a user device certificate comprising a user device public key and a cryptographic nonce used to generate the blinded user device public key, and wherein the method further comprises:

validating, by the access device, the user device certificate;

generating, by the access device, a second blinded user device public key using the user device public key and the cryptographic nonce; and

comparing, by the access device, the second blinded user device public key with the blinded user device public key, wherein the user device is authenticated if the second blinded user device public key matches the blinded user device public key.

15. The computer-implemented method of claim 10 , wherein the shared secret is a first shared secret, and wherein the method further comprises:

generating, by the access device, a second shared secret using the first shared secret; and

associating, by the access device, the second shared secret with the user device, wherein the second shared secret is used to decrypt subsequent user device data received from the user device.

16. The computer-implemented method of claim 10 , further comprising:

conducting, by the access device, a transaction using the user device data.

17. A computer-implemented method comprising:

generating, by a user device, a cryptographic nonce, the cryptographic nonce being a randomly generated value or a pseudo-randomly generated value;

generating, by the user device, a blinded user device public key by obfuscating a user device public key using the cryptographic nonce, the user device public key associated with a user device private key;

generating, by the user device, a shared secret using an access device public key of an access device, the user device private key, and the cryptographic nonce, the shared secret being different from the cryptographic nonce;

encrypting, by the user device, user device data using the shared secret to obtain encrypted user device data; and

sending, by the user device, a message including the blinded user device public key and the encrypted user device data to the access device, thereby allowing the access device to generate the shared secret using the blinded user device public key and an access device private key corresponding to the access device public key and to decrypt the encrypted user device data using the shared secret.

18. The computer-implemented method of claim 17 , further comprising receiving, by the user device, a request message including the access device public key from the access device, wherein the generating of the shared secret by the user device is not based on any other keys from the access device besides those included in the request message, and wherein the generation of the shared secret by the access device is not based on any other keys from the user device besides those included in the message.

19. The computer-implemented method of claim 17 , further comprising generating a session key using the shared secret, wherein the encrypting of the user device data further uses the session key.

20. The computer-implemented method of claim 17 , wherein the user device data comprises a user device certificate, and wherein the access device authenticates the user device using the user device certificate and the cryptographic nonce.