Programming on-chip non-volatile memory in a secure processor using a sequence number
An improved secure programming technique involves reducing the size of bits programmed in on-chip secret non-volatile memory, at the same time enabling the typical secure applications supported by secure devices. A technique for secure programming involves de-coupling chip manufacture from the later process of connecting to ticket servers to obtain tickets. A method according to the technique may involve sending a (manufacturing) server signed certificate from the device prior to any communication to receive tickets. A device according to the technique may include chip-internal non-volatile memory to store the certificate along with the private key, in the manufacturing process.
1. A device comprising:
on-chip non-volatile (NV) memory including:
a secret seed random number;
on-chip writable memory including:
a stored sequence number;
a means for receiving a request for a device certificate;
a means for initializing a state variable in the on-chip writable memory to an initial value in response to a power up event of the device;
a means for computing a key as a function of the secret seed random number and the sequence number;
a means for incrementing the sequence number;
a means for storing the incremented sequence number;
a means for generating a first random number as a function of the key and the state variable;
a means for incrementing the state variable;
a means for creating the device certificate based on the first random number and the request for the device certificate, the device certificate adapted to provide a security signature for accessing protected resources by a secure application;
a means for executing at least a portion of the secure application, the executing using at least a portion of the protected resources;
a means for clearing the state variable from the on-chip writable memory before a power down event of the device.
2. The device of claim 1 further comprising a means for generating a second random number using the key and the incremented state variable.
3. The device of claim 1 , wherein the means for computing the key and for generating the first random number is selected from a group consisting of cryptographically strong encryption, decryption, and hash functions.
4. A method comprising:
receiving, using a processor, a request for a device certificate;
initializing, using the processor, a state variable in on-chip writable memory to an initial value in response to a power up event of a device containing the processor;
computing, using the processor, a key as a function of a secret seed random number and a sequence number;
incrementing, using the processor, the sequence number;
generating, using the processor, a first random number as a function of the key and the state variable;
incrementing, using the processor, the state variable;
generating, using the processor, a second random number using the key and the incremented state variable;
creating, using the processor, the device certificate based on the first random number and the request for the device certificate, the device certificate adapted to provide a security signature for accessing protected resources by a secure application;
executing at least a portion of the secure application, the executing using at least a portion of the protected resources;
clearing the state variable from the on-chip writable memory before a power down event of the device.
5. The method of claim 4 , wherein computing the key comprises executing one or more of: cryptographically strong encryption, decryption, and hash functions.
6. The method of claim 4 , wherein generating the first random number comprises executing one or more of: cryptographically strong encryption, decryption, and hash functions.
7. The method of claim 4 , wherein the key is one or more of a public key and a private key.
8. The method of claim 4 , wherein the secret seed random number is stored on an on-chip non-volatile (NV) memory.
9. The method of claim 4 , wherein the sequence number is a stored sequence number included in the on-chip writable memory.
10. A system, comprising:
an on-chip non-volatile (NV) memory including a secret seed random number;
an on-chip writable memory including a stored sequence number;
a client-side interface associated with a registered client;
a certificate generation module;
wherein, in operation:
the client-side interface is configured to receive a request for a device certificate and to transmit a validated device certificate;
the certificate generation module is configured to:
initialize a state variable in the on-chip writable memory to an initial value in response to a power up event of a device containing the certificate generation module;
compute a key as a function of the secret seed random number and the sequence number;
increment the sequence number;
generate a first random number as a function of the key and the state variable;
increment the state variable;
create the validated device certificate based on the first random number and the request for the device certificate, the validated device certificate adapted to provide a security signature for accessing protected resources by a secure application, at least a portion of the secure application executed on the system, the execution using at least a portion of the protected resources;
clear the state variable from the on-chip writable memory before a power down event of the device.
11. The system of claim 10 wherein, in operation, the certificate generation module is configured to generate a second random number using the key and the incremented state variable.
12. The system of claim 10 , wherein computing the key comprises executing one or more of: cryptographically strong encryption, decryption, and hash functions.
13. The system of claim 10 , wherein generating the first random number comprises executing one or more of: cryptographically strong encryption, decryption, and hash functions.
14. The system of claim 10 , further comprising a server comprising:
a certificate database storing a registered device identity corresponding to the registered client;
a certificate request module;
a server interface communicatively coupled to the client-side interface;
a certificate verification module;
wherein, in operation:
the certificate request module creates the request for the device certificate based on the registered device identity;
the server interface transmits the request for the device certificate to the client-side interface and receives the validated device certificate from the client-side interface;
the certificate verification module verifies the validated device certificate.
15. The system of claim 14 , wherein:
the server comprises a pseudo random number (PRN) generator configured to generate a second random number; and
the certificate request module creates the request for the device certificate based on the second random number.
16. The system of claim 10 , wherein the key is one or more of a public key and a private key.
17. The device of claim 1 , wherein the key is one or more of a public key and a private key.
18. The method of claim 1 , wherein the method is executed in response to the power up event of the device.
19. The system of claim 10 , wherein, in operation, the request for the device certificate occurs in response to the power up event of the device.