System access using a mobile device

1. An apparatus, comprising:

one or more processing elements configured to:

generate a first ephemeral key pair that includes a first public key and a first private key;

determine a second public key generated by a system, wherein the second public key is included in a second ephemeral key pair;

generate a first shared secret using a key exchange function that uses the first private key and the second public key as inputs;

generate a derived shared secret using a key derivation function that uses at least the following inputs: the first shared secret, the first public key, and a public key of the system previously established during a pairing session between the apparatus and the system;

generate a signature by signing transaction information with a private key of the apparatus established during the pairing session;

encrypt the signature and information identifying the apparatus based on the derived shared secret;

verify a signed certificate received from the system using the public key of the system, wherein the certificate is signed with a corresponding private key of the system established during the pairing session; and

in response to verification of the signed certificate, transmit the encrypted signature and information to the system.

2. The apparatus of claim 1 , wherein the apparatus is configured not to send information identifying the apparatus to the system until after verification of the signed certificate.

3. The apparatus of claim 1 , wherein the key exchange function is an elliptic curve Diffie Hellman (DH) function.

4. The apparatus of claim 1 , wherein, to share access to one or more functions of the system with another device, the apparatus is configured to:

receive a certificate signing request from the other device;

verify the received certificate using a root certificate of an authorized entity associated with the other device;

authenticate a user of the apparatus;

sign the certificate using the private key of the apparatus established during the pairing session with the system; and

transmit the signed certificate to the other device.

5. The apparatus of claim 4 , wherein the certificate signing request and the signed certificate are transmitted via a direct wireless connection without using a wide area network.

6. The apparatus of claim 4 , wherein the apparatus is configured to encrypt a security token for the system and transmit the encrypted security token to the other device.

7. The apparatus of claim 6 , wherein the apparatus is configured to encrypt the security token using a public key from the other device and store the security token in a mailbox location associated with the public key from the other device.

8. The apparatus of claim 4 , wherein, in response to revocation of the sharing access by a user, the apparatus is configured to send a revocation message; and

confirm revocation of the sharing access based on a revocation receipt from a secure circuit of the other device.

9. The apparatus of claim 1 , wherein, during a pairing process, the apparatus is configured to generate a certificate that embeds configuration information for a digital key data structure and sign the certificate using a private key of a secure circuit of the apparatus, thereby attesting creation of the digital key data structure according to the configuration information.

10. An apparatus, comprising:

one or more processing elements configured to:

generate a signature by signing transaction information with a private key of the apparatus established during a pairing session with a mobile device;

transmit the signature to the mobile device;

receive an encrypted signature from the mobile device in a response to the transmitted signature;

generate a first ephemeral key pair that includes a first public key and a first private key;

determine a second public key generated by the mobile device, wherein the second public key is included in a second ephemeral key pair;

generate a first shared secret using a key exchange function that uses the first private key and the second public key as inputs;

generate a derived shared secret using a key derivation function that uses at least the following inputs: the first shared secret, the first public key, and a public key of the apparatus previously established during the pairing session;

decrypt the signature using the derived shared secret;

verify the signature using a public key of the mobile device established during the pairing session; and

authorize one or more actions based on the verification.

11. The apparatus of claim 10 , wherein the apparatus is configured to:

receive a certificate from another device signed using a private key of the mobile device established during a pairing session during an asymmetric authentication procedure; and

authorize one or more actions based on verifying the certificate.

12. The apparatus of claim 11 , wherein the apparatus is configured to access an encrypted security token stored in a mailbox to determine whether to authorize one or more actions based on verifying the security token.

13. A non-transitory computer-readable medium having instructions stored thereon that are executable by an apparatus to perform operations comprising:

generating a first ephemeral key pair that includes a first public key and a first private key;

determining a second public key generated by a system, wherein the second public key is included in a second ephemeral key pair;

generating a first shared secret using a key exchange function that uses the first private key and the second public key as inputs;

generating a derived shared secret using a key derivation function that uses at least the following inputs: the first shared secret, the first public key, and a public key of the system previously established during a pairing session between the apparatus and the system;

generating a signature by signing transaction information with a private key of the apparatus established during the pairing session;

encrypting the signature and information identifying the apparatus based on the derived shared secret;

verifying a signed certificate received from the system using the public key of the system, wherein the certificate is signed with a corresponding private key of the system; and

in response to verification of the signed certificate, transmitting the encrypted signature and information to the system.

14. The non-transitory computer-readable medium of claim 13 , wherein the operations further comprise:

sharing access to one or more functions of the system with another device, including:

receiving a certificate signing request from the other device;

verifying the received certificate using a root certificate of an authorized entity associated with the other device;

authenticating a user of the apparatus;

signing the certificate using the private key of the apparatus established during the pairing session with the system; and

transmitting the signed certificate to the other device.

15. The non-transitory computer-readable medium of claim 14 , wherein the certificate signing request and the signed certificate are transmitted via a direct wireless connection without using a wide area network.

16. The non-transitory computer-readable medium of claim 14 , wherein the operations further comprise:

encrypting a security token for the system and transmit the security token to the other device.

17. The non-transitory computer-readable medium of claim 14 , wherein the operations further comprise:

in response to revocation of the sharing access by a user, sending a revocation message and verify a revocation receipt.

18. The non-transitory computer-readable medium of claim 13 , wherein the operations further comprise storing one or more settings in a secure mailbox that is accessible to the system to determine parameters for one or more authorized actions.