Programming non-volatile memory in a secure processor
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 method comprising:
providing a number to use as a small-signature private key;
computing a signature with a small-signature algorithm;
programming, by a manufacturer during the manufacturing of a device, a compressed certificate into a chip-internal non-volatile memory of the device, wherein the compressed certificate includes a device ID, the small-signature private key, an issuer ID, and the signature;
enabling, in operation, a calling application to obtain a device certificate generated at the device using the device ID, the small-signature private key, the issuer ID, and the signature of the compressed certificate, wherein the device certificate is a function of the device ID, the issuer ID, the signature, and a public key, wherein the public key is a function of the small-signature private key, and wherein the device certificate is larger than the compressed certificate.
2. The method of claim 1 , further comprising programming the number in read-only memory (ROM) of the device.
3. The method of claim 1 , further comprising generating the number as a secret seed random number.
4. The method of claim 1 , further comprising computing the number using an elliptic curve digital signature algorithm (DSA).
5. The method of claim 1 , further comprising:
receiving a request for the device certificate from the calling application;
reading the device ID, the small-signature private key, the issuer ID, and the signature from the non-volatile memory of the device;
computing the public key as a function of the small-signature private key and common parameters;
constructing the device certificate as a function of the device ID, the issuer ID, the public key, the signature, and the common parameters;
providing the device certificate to the calling application.
6. The method of claim 1 , further comprising incrementing a runtime state of the device.
7. The method of claim 3 , further comprising:
receiving a request for a random number from the calling application;
generating the random number from the number;
incrementing a runtime state of the device based on the generated random number.
8. The method of claim 3 , further comprising:
generating a key from the number and a sequence number;
receiving a request for a random number from the calling application;
generating the random number from the key and a runtime state of the device;
incrementing the runtime state of the device based on the generated random number.
9. The method of claim 1 , further comprising:
receiving the device certificate;
storing the device certificate in system external storage;
retrieving the device certificate from the system external storage as the device certificate is needed.